Hard To Start

truckin · June 4, 2008

I have a 93 GMC 1500 4.3L V6 that has recently got a horrible problem with starting. It has 230k miles on it and I have done 90% of the work and maintenance myself so I'm pretty familiar with it.

Last week out of the blue one day it wouldn't start for me on the first try. I think I had to crank it 3 times to get it to start and run. As the week progressed the problem got worse and now it simply wont start untill the engine has reached normal operating temperature. Actually it starts fine everytime it just wont stay running for more than 5 seconds untill it reaches normal operating temperature.

So I started with the basics, fuel filter and line check, air filter replacement, and i replaced the IACV since i know that i had not done that before. Problem persisted so I checked for vacum leaks. I couldn't find any leaks in the vacum system but figured it was easy enough to replace the gaskets on the throttle body on up to the air filter. That seemed to help as it only had to reach about 1/2 normal operating temperature before the truck would run but that still like 20 or more starts just to pull out of the driveway. So the next choice was the 2 colant temperature sensors. The colant gauge has always and is still reading correct so I didn't mess with that one (the one on the side of the engine that has one wire connected to it). I did however go ahead and replace the other one (the one on top of manifold with 2 wires connected to it) as it was only $14 and another part that i know i have never replaced before. The problem still persists though so now I'm stumped. So I grabbed my trusty paperclip and checked the codes. Only codes it gave were 32 and 54. 32 = EGR failure, and 54 = fuel pump relay low voltage.

Now the fuel pump I had replaced just over a year ago, I even had to have it done twice cause the first replacemnt was bad right out of the box. I did not do this repair myself though because it messy, time consuming, and I had the extra cash at the time. I did however do the EGR replacement abotu 4 years ago when I replaced the waterpump.

So would if the EGR was not working properly would that keep the truck from running untill it reaches normal operating temperature? I am highly doubtful that the fuel pump relay is the problem since it was replaced a year ago and also because the truck runs perfect once it reaches norm temperature. If there was low voltage to the relay then i should be having problems during hard acceleration which is not the case. Or maybe someone has had this problem before and has got a better solution?

I have searched all over the web, Haynes, and Chiltons and can find nothing that relates exactly to my problem. (truck wont stay running untill it has reached normal operating temperature) I find lots of "wont start when cold" and similar issues but thats not my problem as my truck start easily every single time it just wont stay running untill it gets to the right temperature.

I need to get this fixed in 2 days or else I will be driving my Hearse that has a V8 GM 501 in it. I drive about 60-70 miles a day and gas is killin me just with my V6 truck. I dont even want to think about the gas for that kind of comute driving a 7,000+ lb car with a Gm 501 in it. Thanks in advance.

truckin · June 6, 2008

WOW! Not even one guess. Uhm bump ...

95Sierra2500 · June 6, 2008

I would find that fuel pump relay and check it out (sorry, not sure where it's at on your truck). Not the pump itself, but the relay that controls when the pump is on/off. Also, check the fuel pressure and make sure it doesn't drift down. Your truck will require more fuel to run when it's cold than when it's hot, so if your fuel pressure isn't up to snuff it will stall out on you. If it's not up to snuff but holds steady I'd say it's your pump, if it is up to snuff but won't hold steady I'd say it's your fuel pressure regulator. You could also have bad injectors after 15 years of service, since it's not typical to replace them but they do eventually wear out. I would also consider checking out the EGR, though I doubt that would keep it from starting and running (I have a bad EGR on my '95 but it fires right up and runs like a champ).

Beyond that, I'm not sure what else could be your problem. Maybe check all the plugs for gap/proper burn condition? I'm sure you take care of it, but it's possible that after 15 years some of the carbon build up let go from the combustion chamber and fouled out a couple plugs? I doubt that's the case, but it's something else to check.

truckin · June 9, 2008

The relay is on the firewall under the "relay cover" apparently. Thats where the fuel pump fuse is supposed ot be as well. So I'll have a look at that tomorrow. I read what Haynes had to say on the subject of fuel pump relay and its a little puzzling. they say to check the relay,

1. start the engine

2. let it run at idle

3. while engine is running disconnect the relay

And now the odd part

4. if the engine stops then the oil pressure switch is faulty

I dont quite understand that one. If you unplug the fuel pump relay while the engine is running and thus the engine dies then the oil pressure switch is bad?

Then they go on to the next check.

1. If engine keeps running when relay is pulled put it back and turn off the engine

2. use a test light to probe the fuel pump test terminal (under the dash)

3. if the light does not come on then the fuel circuit is ok

4. if the light does come on the oil pressure switch is bad

Sorry but again. I understand that if the test light does not come on then you dont have a fault in the electrical circuit of the fuel system. But why if the test light comes on when it is testing terminal "G" (which is the fuel pump terminal) is the oil pressure switch bad? Maybe it should be called the oil pressure switch terminal instead? they list nothing about how to test the realy even under the heading "Fuel Pump Relay Check." The only options given when doin the checks is that the system is ok or the oil pressure switch is bad. Can the realy not go bad? I know relays can go bad and have replaced many of them on several cars.

I am pretty sure the fuel pump is alright and I checked the fuel pressure at 13 psi. The regulator is a possability though although if the regulator was goin out then the truck should die at least once in a while when driving and that has not happened. I'll probably get a new one just for the fun of it though since i know I have never replaced that before. I had the injectors rebuilt by a very trusted professinal company about 2 years ago. They rebuilt each one untill it was equal to or above factory specs. One of them they had to rebuild 5 times. Also I did a simple check with a strobe light to make sure they were spraying roughly the same amount at the right times. After my last post I also pulled off the EGR. After I cleand the little bit of carbon buildup off I took it to the autoparts store and asked them to vacumm test it. When I first showed it to them they thought I wanted to return it because it look brand new adn all i did was spray some engine degreaser in the ports, used a tooth brush to clean the carbon and rinsed it off. It held vacumm so thats $150 saved. I did also buy an EGR solenoid valve while I was there as it was only $15 and it was another part that I knew I had never replaced before. I have not checked my spark plugs yet though as I replace them every year in July wether they look bad or not.

So on the list for today I will get the fuel pressure regulator, oil pressure switch, and also go through the weird checks for the fuel pump relay. I'll post back a bit later today.

mooreapi · June 9, 2008

The oil pressure switch they are talking about turns the fuel pump back on when the pressure reaches a set minimum.

The way the fuel pump system is supposed to work is:

1 when you first turn on the key, the pump runs for 2 seconds to prime the system, then shuts off the pump.

2 as you crank and the engine starts, oil pressure hits the minimum and turns the pump circuit back on so that it will stay on.

3 if the oil pressure does not hit the minimum (ie. truck doesn't start or oil pump died), fuel pump will not turn back on.

Matt

truckin · June 9, 2008

Interesting and thank you. My oil pressure gauge has been reading what I consider as high for this truck for quite some time (50+). The gauge also shows that pressure goes up as engine speed increases. I just assumed the high pressure readings were caused mostly by worn valve seals and other seals within the engine since the truck has 230k+ miles on it. Note that thats 230k very well maintained miles but still its getting pretty high.

So on the idea of the oil pressure causing my hard to get it running problem, would the truck run once the engine is at normal operating temp if the oil pump, sending unit, or oil pressure switch is bad or failing? Now I would assume that the oil pump is working because if I take off the oil fill cap while the engine is running oil goes everywhere. Also I have not had any overheating problems and no pinging so is it fairly safe to assume that the oil pump is alright? As for the oil sending unit (if this has one) or oil pressure switch the books I have for the engine dont say where it is located nor can I find it on the web. Anyone got a picture of where these parts might be located?

truckin · June 12, 2008

So I have now also replaced the Oil pressure switch, which was a real pain to do, and also the fuel pump relay as it was just $10 at the auto store. The problem persists though with very little change. Had to start it 22 times this morning to get it to stay running. Also this morning was the first time it died on me while driving. When I was about 1 block away from home it just shut off, so i put it in neutral and and started again. That happened twice this morning so actually it took 24 starts to keep the truck running after sitting all night. Note that the truck was not quite up to normal operating temperature when I pulled out of the driveway or when it died while driving. Once it did get up to normal temp everything was fine and it never died on me again. The oil pressure gauge is still reading 40+ at idle and almost pegged to 60 sometimes when driving so I'm pretty sure the oil pump is working. I also removed the oil fill cap last night while the engine was running to check that I had oil in there. Oil sprayed everywhere so I quickly put the cap back on.

I have also taken the truck to a local private shop just down the road and let them have it for a day to see what they could figure out. They have a nice scan tool so I figured it was worth a shot. they were the ones the replaced the fuel pump relay since the truck was showing the code for it. After replacing the relay they called me claming they had fix it and it was ready for pickup. When i got to the store about 30 minutes later of course the engine had cooled down enough that (b)voila(/b), the problem had resurfaced. I had written down for the shop exactly what it was doing, how many times it took to start it usually, and a list of all the parts I had just replaced on the truck. I also gave them all the old parts so that they could compare them if need be. When I came back to pickup the truck and the problem had came back I mentioned again to them that the new IAC valve had not extended to the same length as the old one when I pulled it out to do a second check on it. They said since the scanner tool they use did not read anything wrong with the IAC valve that the new part was working properly. That was my only guess as to what could still be causing my problem.

I need to have the truck to go to work tomorrow wether it is running correctly or not. Looking for a little help. Thanks.

05W/T · June 12, 2008

When I was having trouble with my 89 TBI, the dealership diagnosed the problem by unpluging sensors until it ran better. Running a computer scanner on these trucks dosen't provide much information to go with. Try unpluging sensors everytime the truck stalls, and see if there is any change.

Brian

truckin · June 13, 2008

Done that already when I replaced each of the sensors listed in previous posts. And to add to it, I have now also replaced the throttle position sensor because the scan tool that you say doesnt give much info showed it was reading 40-42 when it should be closer to 50 or just above that. The scan tool also showed that the brand new coolant temperature sensor (2 wire one) was reading 20 degrees too high so I re-replaced that one as well. The O2 sensor was done last year. So I've pretty much checked all the old sensors and replaced them with new ones just to be sure, and then checked all of the new ones to be sure they are working properly.

You are most likely talking about the scanners you buy from auto parts stores. Thats not what the mechanic is using. Hes using the the three piece large red scanner made for GM techs at the dealerships (the one that has GM molded into the plastic). It shows quite a bit of info.

The last idea I have is the fuel pressure regulator might have a small leak or not allowing the right amount to flow. I would think that it is more likely that it would be stopped up a bit and thus not allowing enough fuel through to keep the engine running when its cold. On the other hand I get pretty bad gas mileage so it could be leaking. When I drive the truck I drive it about 40-50 miles a day and it uses $20 or more in gas to do so (just over 1/4 of a tank). Since its a 21 gal tank then thats roughly 5-6 gal easy and sometimes 7. With 5 gal of gas I should get roughly 75 miles but I'm getting more like 40. Maybe thats because it all city driving and never on the highway but it still seems a bit off. Would the truck run rough all the time if the fuel pressure regulator was going bad? Would there be any other obvious signs besides black exhaust as my does not have that.

Any other ideas of course are more than welcome. Thanks.

truckin · June 14, 2008

Well I got the truck back from the mechanic today as I need it today and tomorrow to go to work. He was unable to fix my problem though because hes just as stumped as I am. He even called 5 of his buddies, he said, and they are all just as clueless. Each said that they were glad that its my mechanics problem.

The things that were done are: replaced throttle position sensor, colant temperature switch, pcv elbow that connects to the throttle body as it had a slight vacumm leak, throttle body gasket (again because he wanted to be sure there was not a leak there), all the electrical parts under the distributor cap including the pickup coil, and the ECM. The problem still persists though.

Whats really unfortunate is now there are more problems than when I brought it to the mechanic. When starting the engine it reves quite high as if the gas pedal was being held about 1/4 down. No part of the throttle is sticking though. My truck does not have a tach so I dont know how high the reves are but its high enough that the speedometer fluctuates from 10-15mph while still in park. Because of this the truck tends to get to running temperature faster and thus only requires 5-8 times starting it. The problem is that while the engine is doing this, tapping the throttle does not stop it. Also the engine is now pinging at all speeds driven so far 10-35! My engine has never pinged! Another thing is that the engine stumbles when coming to a stop as if its going to die. Once the truck is stopped the stumble stops. It has not died yet while trying to stop but I have not driven it to work yet to test (25+ miles one way). These are all fairly minor problems that I can address and fairly quickly fix once my original problem is solved. Its just rather irritating that my almost perfect truck is now going to ping all the way to work and back for 2 days and if happens to die while driving or coming to a stop I'll be screaming more than a few choice words/explatives.

So once again I will restate my problem in hopes that someone can help me. The truck starts fine but it will not stay running untill it has reached normal operating temperature which is roughly 110-120 degrees. this requires me to start it 5-30 times in order to get it running. Once the engine is up to temperature the truck runs great with no problems.

guido · June 15, 2008

I'd love to know the answer to this one - my 5.7L is doing EXACTLY the same thing. I'm leaning towards intake manifold gaskets, not sure though.

truckin · June 15, 2008

Well the drive to work today went quite poorly. The truck was now pinging, misfiring, and backfiring so much and so horribly that it would die at stop lights. When I got to work I put it in park and I guess the momentum that is held by the transmission parts rotating was no longer present and the bacfire was enough to stall the engine. I was rather stunned by this so I sat there and tested it for a bit, restarting it several times and letting it run untill it would stall itself out or backfire and die. Note I had no trouble getting the engine to run at this time because it was at opperating temperature. While in park the truck would not run for more than 3 minutes although sometimes it was able to stumble through the misfiring and or backfiring and keep on running. When it was time to go home the truck fired right up with no problem and I sat there for 5 minutes and it didnt die. On the way home I kept my foot very slightly on the gas to keep the rpm roughly at 1000. I did this by sound though as it does not have a tach. At rpm's just above idle (probably 800) to about 2500 I was unable to hear pinging or any misfiring except when going up a hill. Above 2500 the ping was quite prevalent though. The other thing I noticed driving my truck today was theat the oil pressure was all over the place, ranging from 10 to peged at 60. Sometimes while at idle at stop lights it was even pegged at 60.

Refering to my previous post what might the mechanic have done to cause my truck to run so horribly? I doubt that he forgot to replace the distrubutor weight but maybe its not put on correctly or tight enough?

Having my oil pressure go all over the full range of the gauge gave me an idea though. If the truck uses an oil pressure switch to run the fuel pump once the truck has started maybe my original problem is with the oil pump. Maybe the switch only reads a certain range of pressure correctly and anything over or under that it sends a different voltage or sporadic voltage to the fuel pump? It seems kinda of far-fetched untill you think of a situation where say the oil pump was creating twice as much pressure as it should be (120 instead of 60max). A switch that was designed to read oil pressure in the range of 15-60 and then switch on a fuel source as long at it continues to recive pressure is not going to be able to opperate correctly at 120. Maybe it would cause it to switch on and of rapidly (pulse), or maybe send the wrong voltage (too high/too low), or maybe it wont work at all. Any opinions here would be appreciated. I am going to replace my oil pump on Monday no matter what though simply because I'm not going to drive any car where the oil pressure gauge is maxed. If the gauge is ever maxed then it becomes useless as the pressure could be well over the max reading.

I also picked up a fuel pressure regulator (FPR) today that I will put in on Monday. My mechanic swore up and down that there was no way the FPR could be causing my original problem but he was unable to fix my problem given the same # of days that I have worked on it and he has even made it run worse so I figure, what the hell. I have only found one instance online of the fuel pressure regulator causing the symptoms my tuck has. Oddly enough though the guy that had this problem has the exact same type of truck. So that gives me a little confidence in replacing the FPR which is a $60 part the size of a ping pong ball.

Ideas, comments, crossed fingers are welcomed and appreciated.

cammiller · June 15, 2008

Have a close look at the relucter in the distributor. I have seen them where the relucter comes loose and starts messing things up. The last one I had would run for a min or so, then stall. I had to replace the distributor shaft and pick up coil to fix it.

truckin · June 15, 2008

Well the reluctor has to be removed in order to get to the pickup coil which was replaced by the mechanic. So your thinking that the reluctor is sometimes touching the pickup coil? that could be the cause of my most recent problems but still doesnt apply to the original problem (Engine starts but will not run untill at operating temperature). Also the distributor rotates at such high rpm that it would seem if the reluctor wsa touching the coil at some point there would be a lot more misfiring/stumbling. At the moment you can set your watch to the stumbling as it occurrs exactly every 5 seconds when the engine is at idle and the stumbling lasts for 1.5-2 seconds.

I took the truck back to the mechanic this morning because it is undriveable as it is now with pinging, misfire/backfire, and dieing at stop lights and at idle while in park. I did have a quick look under the hood though to make sure the plug wires were put on in the right order and all secure. The only thing I noticed wrong or different was that the mechanic has for some reason chewed up the wires that go to the ignition coil. By "chewed up" I mean they used some wire strippers and and opened some of the wire insulation so that the copper wire could be accessed. I assume he was looking for the tach wire. Rather odd because the only wire at that point of the engine that is not used is the white tach wire that is sticking out of the harness and very easily accessable. It is kind of disappointing that he did not even wrap electrical tape around the wires where he had opened the insulation because at 20,000 volts the exposed wire could get close enough to be picking up electrical fields from another wire.

Still looking for ideas on why the engine wont stay running untill at operating temperature.

guido · June 15, 2008

truckin - FWIW, my 2000 5.7L was doing exactly the same thing, ran fine hot, but after sitting overnight it was as you said - would fire up no problem, but stall within a few seconds. And like you said, after restarting it about 20 times I finally got it to stay running, but it would surge up and down for a while before it smoothed out. Anyway, truck was eating coolant so I figured intake manifold gaskets. I pressure tested the cooling system today and bingo, leaking between the manifold and block front and rear. Check your coolant level - if it's gradually going down with no visible leaks, then it might be the same problem. Just a thought.