1996 5.7 / Intermittent loses power-Bogs down. Died twice at StopLight. Starts right up and runs fine mostly

[thx1138v2]

I just bought another truck after crashing my previous '94 Sierra. It's a 2007 Sierra with only 108K miles on a 4.3L engine. It's a completely different truck from what you have but the symptoms are amazing close to what you are reporting.

My '94 had an OBD I system so reading the codes didn't do much good. I managed to drive it for 257K miles without using a code reader and my '07 wasn't throwing any codes anyway so I just started up the parts canon. I replaced the IAC (had a lot of carbon on it), the CST (also had a lot of carbon) (the CTS by the thermostat housing but on the '07 there's only 1 on the driver's side of the head), and since it seemed to be carbon related I went ahead and put 20 ozs of Seafoam in the gas. That cleared up most of the problems.

I checked the fuel pressure and it was right at 60PSI, maybe 59. I also cleaned the MAF sensor by soaking it overnight in 90% alcohol and then letting it air dry. Interestingly, once I got it back together it started throwing a MAF sensor code. After I drove it for a while that cleared up on its own.

I was looking for the EGR valve but didn't find one. I'm not sure whether of not it has one. Where it supposedly goes there is just a straight pipe that comes out and runs somewhere down the driver's side of the engine. If you have any info on the EGR on an 2007 GMC Sierra 4.3L Classic I would surely appreciate getting a copy from you.

Since it's running OK I haven't done much to it lately.

I did have one bizzaro thing happen. I came out one morning and it wouldn't start - dead and I mean DEAD battery. I put on my thinking cap on and started to believe it was something to do with the engine computer. I put the battery charger leads on the correct posts (red to positive and black to negative) and DID NOT plug it into the wall outlet. I also did not disconnect the truck's battery cables from the battery. I left it like that for about 2 or 3 minutes, disconnected the charger leads, and tried it. It fired right up! I went to the auto parts store and got a new battery and have not had any problems since.

 

[Erik the Awful]

I did have one bizzaro thing happen. I came out one morning and it wouldn't start - dead and I mean DEAD battery. I put on my thinking cap on and started to believe it was something to do with the engine computer. I put the battery charger leads on the correct posts (red to positive and black to negative) and DID NOT plug it into the wall outlet. I also did not disconnect the truck's battery cables from the battery. I left it like that for about 2 or 3 minutes, disconnected the charger leads, and tried it. It fired right up! I went to the auto parts store and got a new battery and have not had any problems since.

That's extremely common with side post batteries. They loosen up just enough to cause a problem, and the slightest bit of wiggling gets them to connect again. Your battery was probably good.

 

[thx1138v2]

That's extremely common with side post batteries. They loosen up just enough to cause a problem, and the slightest bit of wiggling gets them to connect again. Your battery was probably good.

That's good to know. I hadn't had any problems with my '94 so the problem wasn't with the '07 at all but with the battery. It would stall, stutter, etc. even while driving.

 

[OBS_Trash]

Latest Update to this debacle:

Summary- Intermittent backfire around 60mph. Sometimes I can be sitting at a light and she is idle rough, then just stars purring like kitten. Also Possible Weather sensitive seems to run great most times in cold weather (60 and below), warm weather guarantee backfire. No code when shop scans it. But the issue is intermittent so they don’t believe me it seems like.

Parts Cannon so far:
Spark Plugs / Wires, O2 Sensor
EGR Valve, Fuel Filter, Distributor Rotor and Cap, Ignition Coil, PCV Valve, MAF, Crankshaft position sensor, coolant temp sensor (why not)
Shop did fuel injection cleaning.

On 2/10/24 I replaced the Spider Fuel Injection Module with updated bracket

And what do you know? Still backfire. I’m lost, I feel like it’s a sensor(Intermittent)
like the Crankshaft position sensor I changed is the problem, maybe it was bad or something.

Timing could be an issue, but I assumed the shop scanned it since it’s a backfire issue. I’m going to ask, but to me of timing was off it would be a consistent issue.

Would have been easier to LS swap the damn thing which I guess is on the table now. I just really wanted to keep it OG 350 until I get a square body then swap that.

Any other ideas? I head ECM maybe

 

[Ole2tone]

1996 - 5.7 - AutoMagic

Just recently noticed tiny bits of bog down, just a small chirp and then she's fine. (Days Ago) - Since then its getting more common, even to point where at a stop light and once in parking lot it died. I was able to restart and purs like a kitten, then out of no where (Bogbog). Like bad fuel

(Few Months ago) A previous endeavor which led me to replacing a wire that burned on my headers - i replaced the fuel filter as part of that troubleshooting

(About a year ago) I previously almost screwed up my Fuel Pump relay housing connections by attempting to hook up a kill switch. But its fine now, i jiggle it and it keeps connection

The previous owner said he replaced the fuel pump (But who knows)

It has Headers and Straight Pipe, Buddy said sometimes if the fuel line is running too close the gas can boil and vapor lock causing this issue. (My thinking is ive had this truck a year and its my daily pretty much, just now this??)

*****Things im going to do:
Order a fuel pressure test kit off amazon and tap the schrader to check pressure.
Change the O2 Scensors

Looking for any other ideas, the one my buddy (Very Knowledgeable) hit me for a loop, i wouldnt have thought that, So im hear to get anything i may be missing. Thanks in advance OBS Fam.

Having same problem. Use to do it a lot a while ago not long after we rebuilt motor. We replaced the oil sensor the other day and I was stuck that night on the side of road cause it kept bogging down. I was stupid and tried cranking it a few more times then normal and killed it. Did not want to crank up at all. Luckily last crank it did it. Drove it straight to house. We checked everything crank sensor(expensive hurt wallet) couldn’t get oil sensor off but we gonna check spark, no clue why we didn’t… Either way we gonna check that if that don’t work it may be that sensor but it shouldn’t. Pretty nerve racking driving and you lose power steering and breaks are tough tough to press and stop. We tryna work on it today after I’m out of school and see why. If you figure it out before us let us know.

 

[OBS_Trash]

I’m being told by a shop that Engine is good and strong, it needs to be tuned. This makes no sense to me, but thought I’d ask in here does this sound right? I mean I replaced all the small parts associated with air / fuel and sensors. And new fuel injection. I just don’t see why that would change the original tuning.

 

[Schurkey]

Lotsa folks upgrade the spider to the electronic-injector version, and don't tune the computer. They get by just fine.

I've heard from our resident computer-tuning guru that GM did make some tweaks to the computer tune when the engines were originally equipped with the electronic injector spider vs. the poppet-injector spider.

I don't see this as a computer-tuning problem. Connect a scan tool, find out what the computer wants you to know.

Fuel pressure testing is strongly recommended, including the cylinder-balance test for injector leakage.