Need Help With Engine Surging/Looping.....

[dorito23]

1999 Tahoe LT
5.7 2 Door 4X4

Codes:
P0440 x2
P0171
P0174

I'm having a bit of a problem and I am hoping someone could point me in the right direction. While I'm driving, the engine will loop or surge (whichever you prefer) about 100 RPMs every 2-3 seconds. Up then down, up then down. And half the time when it does this, the truck will kinda shake like I'm driving on a rough road. The shaking always coincides with the looping and never does it on its own, so they are linked. this has been going on for about a year or so, but it seems to be getting more frequent. I doesnt happen at idol or on the freeway, just between 35-45 mph in 4 gear.

I have been dealing with a few other issues with the truck. I dont want to get off topic, but maybe they are related. It wouldnt start a few months, so I took it to the shop and it had a bad crank sensor. They checked the fuel pressure and said it was fine.

I've had the P0440 code for a while and just ignored it until a month ago when I used a code reader and 171 and 174 were on there also. I changed the MAF sensor, hoping that would fix the codes and looping, fixed neither. Changed all 4 O2 sensors, fixed neither. I also bought a new gas cap hoping that would fix the 440 code, which it didnt.

The fuel guage indicator on the dash wiggles back and forth, but I think thats just the fuel level sending unit and not the pump itself (unless someone else has a different opinion) and I dont want to buy a whole new pump unless I have to.

Again, sorry to ramble on, but I wanted to give as much info as possible. If anyone has an idea, please let me know.

Thanks,

Kevin

 

[Chevyrider619]

Ever since I changed my fuel pump about 1 1/2-2 yrs.ago it also does that..The fuel gauge wigles back an forth...Do u know what those codes are?? I have the hoe as yours but mines 98

 

[kickitandholdit]

i cant give you a direction cause i dont trust my knowledge on that subject but from what i know alot of the time when you have multiple problems it is common to have one cause the other or all of them be connected. i had a buddy that had a shaky/looping motor and manny other problems like tranny was acting weird and stuff and it was all because 1 sensor that went out and to dumb it down a little it confused the whole vehicle so everythings calibration was off basically so you might be in for an easy fix

 

[dorito23]

Thats what I was thinking, with the one thing throwing if off. I was leaning towards something with an air/fuel mixture problem.

I have had the truck 5 years and had the trans rebuilt twice, the last time about 9 months ago.

The 171 and 174 codes indicate its running lean in Bank 1 and 2. Thants why I went for the MAF and O2 sensors first.

The 440 code has to do with a leak in the emissions system so unused vapors dont cause the world to heat up.

---------- Post added at 07:25 PM ---------- Previous post was at 07:03 PM ----------

I have also changed the spark plugs, fuel filter, and intake manifold gasket in the last few months.

 

[kickitandholdit]

it causes there to be excess oxygen in the exhaust and that tells you that you have an exhaust leak.. that is a "who cares" kinda problem haha but you could have unmeasured air coming into the engine and that might be throwing it off, if so, its probably a leak in your your intake manifold gasket.

 

[TheBeast99]

I have had the truck 5 years and had the trans rebuilt twice,

holy crap, why that many times in that short period?

i agree that it's probably just one little sensor or other thing that's messing everything up. it's probably the same thing for my minor warm-start issue... i just wish i knew what it was.

probably a leak in your your intake manifold gasket.

i dunno which is worse, having a slow leak or having the gasket just BLOW like mine did all of a sudden. good thing i was close to my mechanic and dropped off my truck. he said if i'd kept driving it i would've blown the block.
thank god for the temp gauge or else i'd have never known. the truck showed no symptoms whatsoever.

 

[kickitandholdit]

i dunno which is worse, having a slow leak or having the gasket just BLOW like mine did all of a sudden. good thing i was close to my mechanic and dropped off my truck. he said if i'd kept driving it i would've blown the block.
thank god for the temp gauge or else i'd have never known. the truck showed no symptoms whatsoever.[/QUOTE]

damn

 

[T-Bagg]

I had codes similar to that a while back. It came down to a bad MAP sensor. It was a guy at AutoZone who suggested I replace it. Like Kickitandholdit said, it had my whole system confused. After I fixed that I found that my front drive shaft tore out the wires to one of my O2 sensors.

 

[CHOIDOCKIFODO]

Need Help With Engine Surging/Looping

That is a great design I will think about it tonight and post tomorrow about some ways around you problem the main being getting a fan that size

Edit - What size is it???