Engine stumbling..HELP!

willlgord · March 31, 2006

I have a 99 Yukon with the 5.7 engine. I've owned the truck about nine months, it had 78,000 miles on it when I got it (97,000 now). I noticed it would cut out then, but it would only do it for maybe half a second and it only happened three or four times during the whole nine months. It didn't seem to be a big problem but there was always the question in the back of my head what it was. Well, this past weekend we pulled a trailer on a 1000 mile trip and the problem has gotten much more serious. After a bout of stumbling it would clear up and run perfectly, I thought it might be dirty fuel injectors and put some injector cleaner in the tank but that didn't help. Now it's starting to do it to the point where I'm wondering if it's going to quit all together. When it starts doing it the service engine light might flash but not stay on. I took it in to get the codes read but since the light didn't stay on they said there was nothing to be read (I thought there may be stored codes). Lately when it has a stumbling episode the ABS light will come on and stay on until the truck is shut off and restarted. I've replaced the fuel filter, the cap and rotor so far and dumped in another can of injector cleaner. The engine always idles perfectly regardless of how it's been running. I think the fuel system might be part of the problem since it seems to happen more while the engine is under load, but it will give me trouble sometimes whille going down a hill too. If I give it full throttle when it's stumbling (trying to "clear it out") the engine will ping and there's a spitting sound under the hood. I'm wondering if an electrical problem is the cause since the ABS system is affected. I thought about the plug wires but we drove through a fair amount wet weather and it didn't make the problem any worse. Could it be the coil? Please help!! I have another long trip in a week and all my money has to go for gas, otherwise I'd already have it at a shop! Thanks... Bill

ChevyTech007 · April 3, 2006

Need to check you exhaust back pressure first, then check fuel pressure under a load.

atboley · August 31, 2007

Hello all....I am new to this forum and I have a similar problem with my 01 Tahoe....the fuel guage will drop to empty and the "low fuel light " goes on for no apparent reason. Then it will jump back up to normal, then it will move to somewhere in between empty and the right amount of fuel. I have resorted to filling the tank and counting the mileage between fill ups as I cannot rely on what the fuel guage says...any info on this topic would help a great deal...I hope I am posting this correctly as I do not see a way to ask a question on this forum....thanks

95% of the time a problem like that is a bad fuel level sensor, the cartridge gets corroded or the fingers that slide on the cartridge get bent... start with replacing it and that should fix it,

you can pick up the sensor alone for fairly cheap but you have to drop the gas tank...

willlgord · April 3, 2006

I think the fuel pump or the electrical for it might be the problem. I've also noticed (but wasn't sure of it before) that the fuel gauge drops when the engine stumbles. I'm thinking that the electrical connection to the fuel pump and tank sending unit is the problem, does the power for the sending unit go through the pump relay too? (probably not) Maybe it's a bad relay if it does. I haven't had time to check this out yet

Thanks for the help.

ChevyTech007 · April 3, 2006

that the fuel gauge drops when the engine stumbles

Well that changes everything, first I would check ground G404 on the left frame rail close to cross member. If it is OK, pull the tank and check connection at sender. Be sure to check connection under sender also, the harness that goes to the pump. The relay does not feed the level sensor so I don't thing the power side is your problem.

willlgord · April 4, 2006

Just where might this G404 ground be located? Is it near the fuel pump on the drivers side? (that would be considered the left side, right?)

willlgord · May 10, 2006

I found the problem!! Originally I was pretty sure I had a fuel problem so I replaced the fuel pump, filter and pump relay... didn't change a thing. After talking to a shop and showing them the problem I decided it was an ignition problem after which I replaced the coil, plugs and plug wires (I had already put a new cap and rotor in). The truck ran great for a few days then it started stumbling again. It got worse and worse until I noticed it happened mostly after I had hit a bump in the road. My next suspected area was the ignition switch but pounding on the steering wheel to shake the switch didn't do anything so I knew there had to be a bad electrical connection someplace. I probed around under the hood and found that a bundle of wires routed from the top of the engine on the passengers side front had come loose of its clip and was touching the exhaust manifold at the front of the engine. The heat had melted away the insulation (even though the wires were wrapped in some heat resistant tape) and the wires were grounding out now and then (from hitting bumps....speeding up...slowing down). I looked at a friends 99 Tahoe and his clip had let loose also and his wires were pretty close to the manifold too so I'm wondering if this is a common problem.

Bill

P.S. I figure the reason the truck ran better for a few days after putting the coil, plugs and plug wires in was probably from moving the wires around while working on the truck and they took a while to settle back onto the manifold again.

teegee · September 11, 2007

Hello all....I am new to this forum and I have a similar problem with my 01 Tahoe....the fuel guage will drop to empty and the "low fuel light " goes on for no apparent reason. Then it will jump back up to normal, then it will move to somewhere in between empty and the right amount of fuel. I have resorted to filling the tank and counting the mileage between fill ups as I cannot rely on what the fuel guage says...any info on this topic would help a great deal...I hope I am posting this correctly as I do not see a way to ask a question on this forum....thanks

Actually this time I can help , but I still have to reply five times before I can ask why my reverse lights come on when I hit the brakes. The inexpensive fuel level sensor requires dropping the tank, or removing the bed to replace it. It seems to be a common failure. I decided to live off the trip meter. I aready do it with my scoot so...

Joey23 · August 31, 2007

Hello all....I am new to this forum and I have a similar problem with my 01 Tahoe....the fuel guage will drop to empty and the "low fuel light " goes on for no apparent reason. Then it will jump back up to normal, then it will move to somewhere in between empty and the right amount of fuel. I have resorted to filling the tank and counting the mileage between fill ups as I cannot rely on what the fuel guage says...any info on this topic would help a great deal...I hope I am posting this correctly as I do not see a way to ask a question on this forum....thanks

ChevyTech007 · April 5, 2006

G404 is on top of the frame on the drivers side near the tank. On review I would not rule out the ignition switch. The ABS "connection" is what gets me. I hope you understand that it is very hard to diag something that is not acting up in front of me.