Engine Trouble

[2 Amigos]

Hey guys, I got a problem on my 1997 Chevy c1500, 2WD, 5.7Vortec with AUTO tranny. It seems that on 4th gear, and only on 4th gear, at about 1500 RPM my engine starts stumbling. Its hard to describe, but its kinda like a quick "put putting" as it gains speed between 1500 and 1600 RPM. Once past 1600 RPM the problem is non-existant.

Had a performance tranny service 15K ago,
new coil 20K ago,
new spark plugs/wires/cap/fuel filter 1K ago,
recently cleaned air filter (Volant),
replaced all 8 injectors 50K ago,
even with all this the problem still persists. I got rid of my engine misfiring
(got P0300 DTC which is why I changed the plugs, wires, cap, fuel filter and cleaned the air filter. I did not get the DTC again after all these)

only thing I have not serviced yet is the engine oil that has 2700 miles on it and I change it every 3K. Any ideas guys?

[Carnivore]

What plug wires did you get? they could be shorting out if cheep ones, air flow sensor gate resister could be starting to go. A multi meter could show that. No pinging? so timing should be good but could be the advance circuit is cutting out or the mapping is off. A computer diagnosis could help ya out on that.

[2 Amigos]

Wires were bought only a few months ago and they are Accel Extreme Wire Set 9042, 100.00 dollar wires and have worked perfect. Computer shows no DTC's, engine has had pinging since I bought it at 8K ago and only thing that came from the pinging was the misfire, and now even with the pinging with the new plugs and cleaning the filter and fuel filter, i get no misfiring DTC. I was thinking maybe a fuel pump going out? But its wierd it only happens in 4th gear, 1500-1600 RPM and nowhere else on any gear....

[Carnivore]

I wouldn't say fuel pump that would show at higher RPM (stranger things have happened though). You shouldn't have ANY pining which makes me think the fuel injection mapping is wrong (I believe that is FI or is it throttle body?) either way that is where I would start. Those wire are great quality, but cheaper ones can misfire right out of the box that is why I asked. Still could be the airflow box, running some cleaner through it could help and wouldn't hurt. Other thing do you run and fuel additives? I would run a bottle of tecron additive through it to clean the injector/TB and take out some carbon build up.

[Bigworm]

Tony,
Just don't go passed 3rd Gear!!!!!lol
All kidding aside, this problem is kinda weird. Only on 4th gear huh...
Quadrupole-double check all your vacuum fittings. Especially lines coming out of the intake plenum passing close by any hot surfaces. A 97 truck can easily show signs of worn deteriorated lines. Take a flashlight and carefully inspect these lines under the hood. You'll be surprised how much trouble a simple vacuum line can give you. Besides you want to start with the simplest easiest solutions.

[2 Amigos]

Hugo- Happened on reverse today for the first time. And yes I will inspect all my fuel and vacuum lines and make sure they are all ok... Thanks

Carni- yes I did purchase a fuel additive last week when I was first experiencing this problem but im waiting for my fuel to go down til I add it. Also my truck is fuel injected. Cleaned my Volant Air filter with the Recharge kit (Cleaner and Oil) just last week and
still problem persists. Could Fuel Injectors already be dirty at 50K miles??

[Wavehopper]

My thoughts...Definately check vacuum lines but also double check all your electrical connectors to sensors and plug connections to make sure they are seated firmly. I had a similar but a tad worse problem a couple of years ago and it drove me friggin nuts. Took it in and it wouldn't reduplicate for the mech. Finally said screw it and took it to a dealer (Last choice). They couldn't get it to do the same thing and I said try one more time and it acted up for them. Turned out that one of the 3 connectors from my O2 Sensor to my Map was seated but not firmly. Apparently it would kinda wiggle enough to where it wasn't contacting good. Didn't have any more problems after that. But who the hell would have even thought to look at that?

[chance]

has anyone looked at the egr valve it almost sounds like a egr stumble if you jump on the throttle and rpm increases does the the problem go away?

[2 Amigos]

Yes it does Chance!

[FishFreeWilly]

i think my dad had this problem with his 5.7 triton and it was crack in the manifold i want to say. or the exhaust leak. i know in my truck with the 6.0 turbo i had my EGR valve done but did not have the symptons like you.