93 Gmc 1500 Suddenly Got Louder

UndeadGMC · April 20, 2010

First off I'm not to this site but its been so long ago that I couldn't remember my password/username/ or email I used to register so I jsut made a new account. I wrote all this info down this time.

OK my 93 GMC 1500 V6 TBI suddenly got much louder in the engine bay while driving the other day. Shes got about 360,000 miles on her but is very well cared for. Infact anytime someone sees under the hood the comment on how clean it is or that they have never seen such a clan engine. When it first happened I though oh well one of the exhaust manifolds finally got a crack or a gasket wore out because there was not a noticeable loss in power. My girl drove it 1 day to work since then a total of 12 miles, I just informed her to take it easy and go slow. Today I finally had a chance to get to the auto store and get the gaskets that I thought I needed. On the way there I noticed a fairly significant loss of power and very excessive fuel consumption (about 1/4 tank for 17 miles) along with the very loud engine. So I'm pretty sure I've got a different problem than just manifold gaskets but I was already home by the time I figured this out.

So to discribe the sound, its like when/if the truck is very low on antifreeze coolant on a summer day kinda loud. I learned this sound well as I had a pinhole leak that grew steadily in the radiator for about 3 weeks while I waited on shipping of an all aluminium radiator for it last summer. If you've ever run low on coolant with these trucks I'm sure you know how loud the engine gets and that its not really loud while sitting at idle, just when giving it some throttle. There is no loss of coolant now though and the thermostat is working poperly and engine temp is top notch. the truck still starts up with barely a touch of the key and she idles perfectly. Its only when I start moving it feels like I got a trailer on the back as I'm having to give it more throttle than normal and it gets really loud.

The truck is stock besides a lower temp thermostat, full aluminium radiator, a larger battery, and a 1200 stall torque converter instead of the 850 stall original. All this was done over a year ago or longer and the truck has run fine since up untill now.

So I'm trying to think what parts to suspect could be causing this issue yet still allow the truck to function pretty good, idle perfect, and not overheat in anyway. I have 2 guesses but I'd like to hear what some experts have to say or some other possabilities that I may be overlooking before I got try and diagnose with my wallet.

My 2 cents is saying that it might have something to do with fuel air mixture. The reason I think this is because remembering my radiator problems last year I started to think why does the engine get louder when it loses about 1/2 its coolant in the radiator? Well it will be starting to overheat and thus not running at normal operating temperature. So maybe as a fuel injected engine gets hotter the ECM tries to adjust the air/fuel mix by giving it more fuel depending on air density of course? Not sure if thats accurate but it seems plausable since when the engine is cooler the ECM gives the engine less fuel because the assumption that the fuel is more dense. That would account for the incredibly excessive fule consumption problem I'm getting though. It also would make sense why there is a loss of power once it gets moving. Too much fuel in the fuel/air mix will flood the engine thus creating a loss of power while throttling yet it should still idle near perfect which mine does. Its hard to test that theory since there are so few actual gauges on cars now a days.

I have all day to play with it today so throw me some suggesions or of course if you have had this problem straighten me out please.

I will try and post a video tomorrow also since its hard to diagnose engine problems simply from a written discription of a noise.

Cliff883 · May 28, 2010

I have an 88 with the 305 in it, so I went to check the oil flow with te cap off for you, but I see you already found out that it was normal. But I also wanted to tell you that with the 180,000 my truck sounds the same as yours, and I didn't think of it as loud.

UndeadGMC · June 4, 2010

So I was at work last Saturday around 11pm and while curising at 50mph the engine went back to noraml operation and got quiet again. It was nice to have the lost power back but even better was no more excessivly loud engine. Unfortunatly while driving to the parts store for some cadillac parts Thursday at 2pm the problem suddenly came back again.

Now it was weird when the problem first occured and the engien suddenly got louder. But for it to have this problem for a month and then magically go away for a period of 4 days and then come back again is just plain crazy. Please throw out some ideas as all I can think of is possibly part of the water pump is slipping and it happened to catch back in place for 4 days.

TexasAl · June 4, 2010

Wow, that is crazy. Could this be a mechanical problem in the engine (Lifters?)

jro909 · June 4, 2010

sounds internal, like something getting stuck and unstuck or you have a mouse living in the motor and every once in awhile they move the furniture around i had a buddy that had a mouse living in the air filter houseing and eventually it ate hole through it and it got a little louder...

Nytemare · April 20, 2010

Im no expert, but I've had a simular problem with my '97 5.7L before. Truck started getting louder and louder over a course of a week or so, fuel milage went from poor to crap and I had zero power. The problem on mine was that my passenger side exhaust pipe had cracked inside the manifold. Right where the pipe flanges out at the manifold. I really couldn't see it or even knew it was there untill I kept driving and driving it and then I hit a pot hole and it broke the rest of the way and gave me an open manifold on one side. What it was doing, was allowing my exhaust to excape just enough to make my o2 sensors on that bank think that its not getting the right a/f mixture and was trying to adjust it and making it run like crap. Now i know yours is a TBI but its somthing to check out. Hope it helps and good luck.

+1

Check your exhaust from the manifolds back...you will find something separated.

Nytemare · April 26, 2010

Try rock Auto if you want stock stuff man.

I would just get two ball flanges and make a crossover exactly like the stock one and go with that.

UndeadGMC · April 24, 2010

Well I've been trying for days to get the flange bolts off but nothing has worked. Soaked it in penetrating oil overnight and heateed with a torch the following morning and applying wax to the areas once heated. Broken one bolt head off and nothing is budging. I dont have an air compressor or such tools to use an air chisel to break it lose. So I called 4 exhaust shops and went to 2 and no one will touch that type of work. I just put a C clamp on there to hold it together a bit more so I could get better than 5mpg (currently getting about 10mg which isnt great but better than 5!). Since no one will touch it I am left with either removing everything from the manifold down or trying to hack up the exhaust untill i can get to the bolts to cut them off. Although I'd like to, I am pretty certain if i try and remove the manifolds some of those bolts are going to break off and thus cause me tons more work so I think the best option is to hack up the exhaust with an angle grinder untill I can get at the bolts to cut them off and drill out the bolts & threads on the manifolds. I dont want to drive it afterwards with no exhaust pipe and the O2 sensor just dangling so I was wondering does someone sell that piece of pipe that connects the 2 manifolds and has the Y to go down to the cat? A prefab pipe section is what I'm looking for rather than driving to a shop after wards sounding like NASCAR. Also since none of the shops would help me I'd be reluctant to pay them to do the easy part once I've done all the work.

Also the most helpful of the shops I talked to said it wasn't leaking and that something else was the problem. All he did though was lift the truck with it running and hold his hand to the area to feel a leak. I understand how he could come to that conclusion but he didn't seem to understand when I told him its getting 5mpg without the C clamp on there and about 10 with it on. If I gain 5mpg just by putting a C clamp on a piece of exhaust that appears to be the problem logic says there is a problem there, he wasn't understanding that though. So I stopped at autozone to get a code reader (because it comes with a book that says what all the codes are) not because I don't know how to jump the pins. Sure enough shes giving code 35, which is IAC valve. My IAC was replaced about 8 months ago along with every other sensor up top of the engine because I had a no start problem. But just to be sure I pulled it off this morning cleaned and tested it before reinstalling it. Also cleaned everythign else under the air cleaner just to make sure. Started it back up and it had a high idle like it should till the IAC adjusted. Then restarted it and idle was back to normal and I still have the same problem and its still showing code 35. I pulled the plug off the O2 just to mmake sure it would give me that code which it did. So I'm certain now my problem is the exhaust leak at the flange. Its giving code 35 because theres just too much fresh air getting to the O2 sensor and thus its giving code 35 saying the IAC is stuck open allowing too much air in and therefor overcompensating with way too much fuel (abotu 3-4 times too much depending on the speed which I drive it according to my gas mileage).

Iif someone has a better idea than mine of cutting off all of the exhaust pipe and connectors all the way up to the manifolds with an angle grinder I'd love to hear it because I know this job is going to suck big time. I would like to just cut the bolts off but theres no space to get the angle grinder in there without hacking up the exhaust.

UndeadGMC · April 29, 2010

After hunting all over town I found 2 people that would make the Y pipe for me and the lowest wanted $200 to make it and then more money to install it. So I went over to the junkyard and got lucky. Someone had been there and pulled all the engines completly out of several trucks and left the pieces I need already off the car I just had to pick it up and walk to the checkout counter. I had 4 pipes to choose from but none were exactly like mine so I went with one that had the O2 sensor socket on the pipe like mine is instead of having to weld one on myself. The one I got came off a suburban and the Y merges into a 3" pipe. Unfortunatly this does not allow me to use my old cat converter which is only a 2 1/2" pipe. I ground it all completly clean with the angle grinder and wire wheel then painted it with high temperature paint. I wanted it to be gloss black but I didn't specify gloss to my girl on her way home, so flat black it is.

Cost:

Y pipe = $4.99

gas and electricity for grinding the part = $5 roughly

High Temperature paint = $7.49

Total with tax = Roughly $20 ( a lot better than $200+)

Here it is done with the new flange gaskets and stainless hardware. The springs aren't stainless, I would have had to roll them myself and I don't have time for that. Aside from having the worst looking weld I have ever seen, except for my first attempt at stick welding, I think it looks pretty slick. The stainless hardware cost me about $9 and the flange gaskets we $7 each, so a grand total with gas and estimated electricity about $40.

Wost weld I have ever seen. It looks 100 times better now that I ground it down a bit and painted it.

Some notes:

The original bolts were 3 1/2" long so thats the size I got for my stainless bolts but apparently thats too long. The ones I got will work but 2 of them touch the manifolds when tightened up so I will be getting some 3" ones to replace them later. This will be a 10-20 minute job though next time since I have made it where anyone with 2 14mm wrenches can take off the exhaust with ease.

I went for the 3" outlet on the Y pipe because the others at the junkyard came off V8's and did not have the O2 sensor socket on the pipe (O2 sensor on passenger side manifold). This also meant that I could not use my old cat converter but I didn't think that would significantly affect the exhaust noise. I was very wrong. Its not quite as loud as just headers but its damn close. I will deffinatly be making another trip to the junkyard to pickup a muffler, catalytic converter, or both (if there is space for both under my short bed truck) because it is WAY too loud for city driving. I was unable to tell if my problem was fixed during the test drive because the exhaust was so loud. All I could focus on was keeping a light foot on the gas as to not make so much noise. I did take it up on the highway for a mile so I could gun it just for fun though. I was amazed there was not even one miss or backfire without the backpressure from the cat but thats a good thing I think. Since I used the Y pipe from a suburban it has that nice bolt on connection for the rest of the exhaust system but that also means I will have to use a suburban muffler/cat or cut off the connection I need and attach my own setup to it. I noticed while under the suburban that its muffler was as long and almost as big as my gas tank in my little truck. I'm not sure if I can even fit it in so I'll have to do some measurements before heading to the junk yard. I'd prefer to just use a cat that accepts a 3" pipe and no muffler but i didn't see any when I was there, I'll look harder this time aroudn though. Hopefully I can get this done tomorrow so i can test and see if the problem is still there.

Nytemare · April 24, 2010

Do you have Aluminum or cast iron heads?

Cast Iron heads mean you will likely get all the exhaust bolts out of the manifold....aluminum...probably not.

Either way.... here's our little trick for freeing header/manifold bolts in aluminum, it also works very well with iron heads.

Heat the bolt till its nice and cherry red....smack the head a couple times with a heavy hammer....a large ballpein

Let the bolt cool down to room temperature....hit it with penetrating oil...let it sit for a bit than heat the bolt again to cherry red. this time hit it with a hammer than, when it cools to normal color try and remove it.

Works for us at the shop 99.9% of the time.

The bolts in the flange below I would just blow away with a torch. cut the heads off and slip the lower flange off, than take the manifold off and have the bolts extracted. Just be very careful you don't snap a bolt off in the head.

UndeadGMC · May 29, 2010

Well since no one has any ideas how about I throw a couple questions out there.

Has anyone ever heard of a water pump that went out or was going out but the car/truck did not overheat?

The only other thing I can think is that the injectors that I had rebuilt 2 years ago are out of whack again. This could be likely because I have been using a much lower thermostat since these injectors were redone. Instead of the temp gauge reading 210 all the time it has read about 120-130. A cooler engine will cause the computer to inject considerably more fuel. I have deffinatly noticed that my gas mileage is laughable since the addition of the super low thermostat. By laughable I mean is between 10-12mpg without the AC on. I don't even make a guess during the summer when I use the AC constantly or the laughter could turn to tears. A low temp thermostat is a win all the ay around as long as your not concerned about gas mileage. Keeps the engine much cooler, saving wear on your engine from its arch enemy, heat. And the added benefit if you have fuel injected vehicle, that the computer will automatically increase the fuel added to your intake at all speeds, giving you more power in all ranges.

UndeadGMC · November 1, 2010

Well its been a long time but figured I'd post back to let all know what the problem was. About a month ago I got a coolant leak from near the firewall so I bought a new heatercore and swaped it out in 20 minutes. The old core wasn't and had no signs of leaking when I pulled it out though (it was onyl 3 years old). I alreday had it pulled out so I just kept the replacement in there for good measure.

Since I was already at the parts store I took a stab in the air and bought a new fan clutch that I could just return if mine happend to be alright. Well mine, wasn't alright. The outside shaft seal had warped and come loose. This allowed the fan to be able to rock side to side on the shaft. Put the new one on and voila, the engine got quiet again. It wasn't quiet like before all this started but it was significantly quieter. 3 days after that the waterpump started to leak from the bottom weep hole. The original waterpump in the truck 10 years ago leaked from the top weep hole so it took me a day to figure out where the leak was coming from. I figured the waterpump would be shot since the fan clutch had been shaking all over the place for a month or 2. I also confirmed my thinking that even the 160 degree thermostat and larger radiator couldn't keep the truck from overheating for very long. Now so I had the joy of taking off the fan clutch again to get to the waterpump. With the new pump and fan clutch the truck is back to normal again finally.

So if your truck sounds louder than you think it should 1st thing to check is the fan clutch. Just grab a fan blade with your fingers (with the engine off) and try and shake it side to side. If it moves replace it. The other check for it is to take the fan shroud off and look for any leaks comeing from the fan clutch (the silicone fluid in mine was black). If theres any sign of leaks replace it. I also found out that its recommended to throughly inspect as per the above and or replace the fan clutch every 60k miles. My truck is close to 350k so it was a bit overdue.

jro909 · May 26, 2010

did you try putting a mechanical oil psi guage on and seeing if the electronic guage is just being spedly? is there too much oil in there? idk if maybe the sensor has to relearn(idk i'm not too savvy on old vehicles)

UndeadGMC · April 20, 2010

I've been busy with the truck all morning. I wanted to start out by getting the video up for you guys but Murphys Law came into play and when I went to get in the cab I noticed the drivers side rear tire was flat. To make it even more fun I have a dirt drive way so I had a fun time getting it jacked up. Anyways I got the tire on but while I was in there I went ahead and cleaned off all the brake parts, the spare rim, the spare winch, anbout 20 other things I noticed needed a little TLC.

I havent had time to get her out on the road yet but I've done a thorough inspection of the exhaust system since this was the first suggestions given and also my first guess. Heres the Exhaust Y, looks good.

Everything checks out good I think but I have some pictures of it all just incase someone can spot something I missed.

http://s149.photobucket.com/albums/s47/sad...500%20V6%20TBI/

Being fully stock still the passenger side manifold had the heat shield that connects to the air intake to preheat incoming air still fully attached.

It took about an hour just to get that thing off so I could examine the manifold. Notice I need a new PCV grommet, thats what happens when you go all winter without opening the hood. The back part of it is still wedged in there but I got it peeled back enough so I could see everything. I'll have to finish taking that off one day when I replace the engine mounts or the manifold gaskets, whichever comes first. By the looks of it, it seems like the enigne mounts will be first as the passenger side one is looking a tad worn while the drivers side one is still perfect. As you can see from the pictures the O2 sensor, its connector, and all wires look really good.

Is there a way to test the O2 sensor?

My "exhaust system" stops about 2 feet after the catalytic converter which puts all the pipe within arms reach. Ahhh the joy of living in a state that doesn't require emissions tests. The only possible leak would be at the manifold to pipe flanges but they felt real tight. I just grabbed the pipe in several places and shook as hard as I could to try and get something to wiggle around or come lose abit. At the flanges 2 of the 3 bolts are very tight and the 3rd is left lose I assume to allow for expansion when heated. The flange on the passenger side has this 3rd bolt very lose (I can turn it by hand) but the connection did not appear to have or make any gap while doign the shake test.

See how that 3rd bolt shown clearly in this picture is well below the top of the flange unlike teh other 2 that are tight. Is there a trick to getting these bolts off because turning it doesn't make it come out? The drivers side manifold was tip top so I didn't include any pictures.

MaForrest, did your truck still idle perfect and without excessive engine noise? It seems like if my problem was an exhaust leak then it would be virtually non-existant when the truck is first started since all the pipe and connections feel tight, but thats not the case. It should aslo get worse as its driven because the exhaust will be expanding thus widening any gap, similar to yours expanding the crack. If theres a way to at least test if the O2 sensor is sending some kind of output then that should I think tell me that I just need to tighten that 3rd bolt on the flange. I know 1 wire is to preheat it and I guess the other 2 are input voltage and output. Any ideas which wire does what?

UndeadGMC · May 28, 2010

Yea I opened the oil cap one time maybe 3 years ago while the engine was running (or maybe while a friend was starting the truck) and I got an oil bath. So I made sure to never do that again untill just the other day. I don't know why I got drenched in oil that day, I guess it was just a fluke?

Probably my little tiny camera microphonne doesn't do the loudness of the engine justice? If you got a 5 gal bucket and 20 minutes of free time in the shade, drain the coolant, put back 1 gal of it and run the truck for a minute or 2 or maybe a very short drive just around the block. Then you'll know what I mean by a loud engine. If you don't have shade don't bother cause its a real pain to do this sweating all ove the place. (running the truck with only 1 gal of coolant wont hurt anything as long its only for a short trip around the block before the engine has time to warm up to normal operating temperature)

UndeadGMC · April 26, 2010

Nytemare, I'm not sure what type of metal the heads are made out of but if I had to bet, I would go with Iron. Either way I did not want to remove the manifolds because I carefully inspected them to make sure there was no leak there and I know for certain that attempting to get them off will cause more problems or broken bolts because mine are excessivly rusty. Both manifolds look and feel strong so I just wanted to remove all the pipe from the manifold flange down. I will be giving the manifolds and bolts a very through cleaning though while I'm working around that area. I am also going to keep them cleaned and the bolts lubed with penetrating oil for a good long while in hopes that I can remove them with a bit more ease in the future.

Well since my talks with exhaust shops all ended in failure and no one would touch it, I came to the realization that its going to cost me a small fortune to have someone remove this stuff for me. So this morning (about 1pm actually, I'm a late sleeper ) I got out the angle grinder, some channel lock pliers, and the zaws-all and started hacking pieces off. It went pretty fast up untill i got to about 6 inches from the passenger side flange. This is where the channel lock pliers came in handy. I'd use the angle grinder to make cuts in the pipe and pliers to bend and rip it off. You have to get the pipe completly off or down to about 2 inches in length in order to have access to cut off the flange bolts with the angle grinder. To do this you need an angle grinder and hammer since there is not enough room to use the pliers up there, you just pound the pipe inwards on itself and thus giving you access to more pipe to cut off. I also cut the actual flange near the bolt furthest to the top in the picture. (see flange picture near bottom of page)

The manifold looks like theres a crack in this picture but its just groves my screwdriver made.

With the bottom bolt broken as mine is, cutting the flange allowed it to have a little play so I could pry the whole pipe and gasket out of there with a screwdriver once it was about 3 inches long. Then I could fairly easily cut the 2 remaining bolts off with the angle grinder. You have to use a new disc for each bolt though cause you have to cut through the nut and bolt at an angle because lack of room. Without a new disk on each bolt the disk wears out and it wont cut all the way through. If you can get it cut at least 1/2 way through you can beat the bolt and nut off with a hammer. Just be careful that hot bolt doesn't land on you! One burnt right through my comercial door mat so your T-shirt wont stop it 1 bit from burning a permanent hole in your skin. Next changed out to a grinding wheel and ground down what was left of the 2 bolts. Googles came in handy here. I'm not a big fan of googles but dont do this step without them I promise you'll be glad you had them. You have to get whats left of the bolts fairly flat so you can get a good centerpoint to drill them out. I highly suggest leaving about 1/8 of an inch of each bolt sticking out of the manifold hole that way if you mess up while drilling you will have something to grab onto with visegrips in order to get the rest of the bolt out. The flange bolts are 3/8 DIA so I tried a shortcut at first and just attempted to use a 3/8 drill bit, relying on my steady hand to keep the bit from walking. It worked on one but not the other. The proper way to do it (what I did for the second bolt) is use a 3/16 bit to make the pilot hole. 3/16 is small enough you can keep it from walking and not too small that you will snap the bit with any side pressure you have to do to keep it from walking. I drilled the pilot all the way through each bolt. Also have some oil around to dip the bit in, one dip every 10 seconds is the rule I follow, it helps a lot and it saves your bit so you can reuse it. Once the pilot is drilled all the way then switch to the 3/8 bit and just drill out the bolt. If you notice your hole is a bit off center like one of mine was because the bit walked then you have to use several bits in order to not cut into the manifold hole with that big 3/8 bit, with oil on a 3/8 bit you will cut right into the manifold without even noticing it. For my mistake I had to use 4 bits, 3/16, 7/32, 1/4, and 5/16. Notice 3/8 isn't listed for this one. If your hole is off center you wont be able to use the full size 3/8 without damaging the manifold hole. Just get up to the largest bit you can untill its taking off those threads inside the manifold hole. Since you left 1/8 of an inch of the bolt sticking out as I suggested above then you can use a hammer and screwdriver to bend whats left of the bolt inside the hole a bit, grab it with visegrips and thread or pull it out. You can see all the marks left by the screwdriver where I had to beat one of the bolts out useing that that little 1/8" piece I left on there. If you grind the bolts flat to the flange of the manifold and mess up centering your drill then your in for at least another hours work maybe more because you will have to use a sideway cutting bit and TONS of muscle to make it cut sideways through metal.

Heres what it all looks like off the truck. Notcie I didn't take the drivers side flange off. If I can't find the correct replacement pipe to connect the manifolds to the cat then I'm hopeing to just leave that flange on there and use an exhaust connector piece to make the splice. If someone here does point me where to get the pipe then I'll of course remove the other flange and do the job perfect on both sides.

Whole system (the bottom section of pipe in this picture is what I ma needing now)

Exhaust Y to cat clamp (easiest way to remove it is to cut it)

Exhaust flange & gasket (Cut it near the bolt to give it some flex)

Whats left of the flange bolts

6" of exhaust pipe hanging from the flange reduced to scrap

Well as you can see I got my flange off in about 3-4 hours (thats with going back and forth inside to get more tools, lunch break and couple of smoke breaks). I just need to grind it down nice and pretty before putting in the new stuff. I've already got new 3/8 stainless hardware ready to put it all together I just don't know where to get the pipe that goes from the manifolds to the cat and holds the O2 sensor. Does anyone know where I can get one thats to size already? I really don't want to drive to a shop sounding like NASCAR to have them make one.

My cat converter sounds like it has about a shot glass worth of sand in it but no large pieces so I'm going to reuse it since it has a cleanout plug (haha) and my state doesn't have emissions testing.

The cleanout plug