Another hard starter

Tonyb7 · July 5, 2003

Truck: 1997 GMC Sierra Extended Cab, 5.7liter

A few of the other posts regarding starting troubles had similar symptons to what I am experiencing here, but, there are a few differences.

Lately the truck had taken to being very difficult to start in the afternoons while starting relatively easy in the mornings. It would crank and crank, with a few sputters, until eventually catching. Sometimes this would take 10-15 minutes of effort in the afternoon.

A couple days ago it decided to not start all together. It would crank, but no sputters or any other indication that it wanted to run. I left it at my office overnight, in the hopes it would start the next morning. No luck, same problem. Going by the Haynes manual (which seems more helpful for the pre-96 model years for some reason), I tried several things. I wasn't able to find the fuel pump test point (finally found it today, hiding under the relay/fuse block), but instead put a jumper in the fuel pump-relay socket to see if the pump worked. It hummed right along. Put the relay back in, and the engine started after a few sputters. I tried the procedure for testing the oil-pressure switch while I was at it, it passed according to the manual.

The truck runs fine after it starts. And can be started right up again after it has been running. But, if it sits for a few hours, it has the same problem again. Which is fixed by running the fuel pump for 10-15 seconds before trying to start again.

Autozone put their scanner on it, no codes. All fuses check out. Relay checks out (I even tried one from my wife's truck, same result).

So, any idea what the cause of this problem is? Fuel pump? Pressure regulator (I can't figure out any easy way to check the vacuum line as the regulator is underneath the upper intake mnifold). Electrical?

I'd sure appreciate any help.

Thanks.

chev_tech · July 5, 2003

My vote is for fuel pump. Those poppet valve fuel injectors are critical in having enough fuel pressure to open them. When the pump starts to get weak, the hard starts begin. Ive noticed that once running, the injectors take less pressure to stay opening. Without diagnosing, I would say very good chance of pump being weak.

DeezBlueZ · July 7, 2003

You can check your pressure regulator with a mighty vac. Follow the hose that goes to your regulator and hook it to vac. Give it a few pumps..it should hold that vacuum indefinately. Also look for signs of fuel in the vacuum hose..this means your diapragm is leaking. The wifes car had its injectors replaced (Z34 Monte Carlo) under warranty, because they would bleed off when hot, dumping fuel into intake, causing hard and sometimes no starts.

chev_tech · July 7, 2003

The fuel pressure regulator on your motor is under the upper plenum and can't be checked without taking the plenum off. Just a note. Very unlikly on this motor. Also, if the regulator or injectors were leaking fuel, it would run rough after starting for a few seconds until the raw fuel cleaned out. Let us know what you find out.

Sierra5.3 · July 8, 2003

I have been having the same problem with my truck... Just replaced the Fuel pressure regulator and its still having the same problem. Anybody got the part number for the Fuel filter and Fuel Pump???? Thanks

knightrider2000 · July 8, 2003

one for my 99 5.3 is 25176865 called a "modlue" cost me $308.15 at my local dealer.. esh.. and mine still dosent want to start right all the time.. acts like there is no fire to the plugs.. then it will go ahead and start.. does it probley one out of every 10-15 starts ????

Matt G.

Sierra5.3 · July 12, 2003

one for my 99 5.3 is 25176865 called a "modlue" cost me $308.15 at my local dealer.. esh.. and mine still dosent want to start right all the time.. acts like there is no fire to the plugs.. then it will go ahead and start.. does it probley one out of every 10-15 starts ????

Matt G.

Well now........its doing the same thing as yours. When its cold it'll turn but wont catch, so I lay off, put half throttle and it starts up. Gonna try the fuel pump, anyone got the number for a fuel filter for a 99 gmc sierra with a 5.3?

02 Silverado Z71 · July 12, 2003

TonyB7...

Drop your fuel tank. Remove and replace your fuel pump. Install tank. Replace fuel filter while you are at it. Your truck is a 97. About the only thing that goes out on those is a fuel pump!

But really, you have the classic complaint for a bad fuel pump. ALSO: when you replace the pump, pay SPECIAL attention to the wiring terminals at the sending unit (where the truck harness connects to the fuel sending unit) Have seen a few trucks with corrosion built up in the connector. Pretty rare, but does happen.

hosman · July 12, 2003

Great site here....my 99 7.4L is doing the exact same thing. Sporadic hard starting........I've changed fuel filter,plugs, wires and was wondering about the injectors passing fuel into cylinders.The more I check it out the more it points to my injectors. Everything I've done seems to have helped but it still does it. Once it starts, it chugs a little and then cleans and smoothes out. I can see the black exhaust coming out of the tailpipe upon start up,then it cleans up right away. I can smell the fuel also. These symptoms tell me it is way to rich on start-up and takes a few seconds to cleanup. Is this common with bad injectors? It doesn't seem like a fuel pump problem to me,once it is started it runs smooth......no problems.

Would luv to hear if anybody else has had this problem.Thanx,

Tonyb7 · July 13, 2003

Thanks guys. I've been leaning towards trying the fuel pump. I had already replaced the filter. There was hardly any debris in it at all. I'll try replacing the pump and let you know how it turns out.

bigtruck21 · July 15, 2003

anyone got the number for a fuel filter for a 99 gmc sierra with a 5.3?

parts for 99-02 gm

25055052 / GF481 Fuel Filter

Tonyb7 · July 28, 2003

Success!

Thank you very much for the help guys. It was the fuel pump. Here is a bit of a rundown on how it all went (hopefully this will help someone avoid some of the "fun" I had with it):

I finally had the time and funds to give the pump a go. Let me first say, that I will never try that again. Replacing the pump itself took me all of 30 minutes. Getting the tank out of the truck took me around four hours.

Here again, the Haynes manual seems to have illustrations and directions for just about every year but the '97. Instead of the two tank straps that are shown in the book, mine had the rear strap and a forward bracket. The bracket is bolted onto the side fram and extends 90% of the way across the bottom width of the tank. I suppose it would have been a lot easier to get it out by removing the driveshaft first, but by the time I figured that out I had the tank doing a balancing act on my jack.

For anyone who has a '97 1500 Sierra (probably the Silverado to I would assume), I would suggest grabbing a friend and removing the bed rather than trying to drop the tank.

Anyway, after discovering that you _can_ run out of swear words, I managed to get the tank out and on the ground. This was after giving up on trying to disconnect the outfeed fuel line at the tank, and instead doing it at the filter (I'm not sure what GM torqued that dang thing to, but I'm definitely not worried about it ever leaking). I think that was the point when it became obvious it would have been a lot easier doing this with the bed removed and the tank left alone.

After nearly destroying the lockring by beating on the wrong tab with gusto (I'm seriously considering sending some "advisory" illustration tips to Haynes), I finally found the right tab and unlocked the ring with nothing more than hand pressure.

Got the sending-unit/pump out and was finally able to do something that felt positive. Installed the new pump and strainer (AutoZone special, I think the brand was Master). Inspected the wiring harness as per 02 Silverado Z71's suggestion. No corrosion found. Put the unit back in the tank and locked it in. I liked that part of the project, so I'd probably be willing to do that again if someone else yanked the tank, while I looked on with a camcorder.

Putting the tank back in was marginally faster than getting it out. I think it took me about two and a half to three hours. Here I discovered I hadn't run out of swear words after all. It was fairly uneventful, just frustrating trying to get the positioning right to reconnect everything.

Got everything reconnected, and poured in some gas. Tried the ignition briefly, but stopped after a few seconds. I've never worked on the fuel system of a a vehicle with fuel injection before, and wasn't really sure of the best procedure for starting after the system had been drained. I jumped the test port and ran the pump manually for a few seconds. I could immediately tell a difference. I could hear the fuel flowing through the system under the hood (something I didn't hear before). Tried the ignition again and it started immediately.

The only leak I had was at the filter (I think I banged up the o-ring when dragging the line through the frame). Fixing it showed me the difference between a system with a working fuel pump and one with a weak one. The gasoline shower that resulted was refreshing for a minute or so. De-pressurizing the system is definitely the way to go, regardless of wether it seems to be pressurized or not.

This turned out to be a much longer post than I had intended, but hopefully it is useful to somebody. If anyone wants to see some pictures of the ordeal, I snapped a few and can put them up on a site.

Thank you again for the help guys. This forum is truly a great resource.

bigtruck21 · July 29, 2003

sure post them up!

hamhawk · July 31, 2003

Just wanted to post a thanks to those that suggested the fuel pressure regulator, mine's been starting hard for a few weeks now and was just about ready to take it in and pay through the nose, but I replaced the fuel pressure regulator last night and it starts and runs great. I had never heard of that part but with the info on this forum it was a piece of cake to find and replace.