Kumi

1991 4.3
200,000+

Truck has-

New spark plugs
New spark plug wires
New air filter
Fresh oil & filter
New pcv valve
New egr valve gasket & egr has been cleaned


Truck has been running good until a couple days ago. I was driving a friend home and about halfway there,my truck started to sputter under load. It would accelerate but i had to be easy with the throttle and adjust my shifting.

On the way back i gave it a little test by getting to 50mph,and driving in 5th gear like i normally would,then mashing the gas as if i was trying to pass someone,it immediately started sputtering and trying to cut off until i back off the gas and it drove perfect until i mashed the gas again.

I replaced the fuel filter today and discovered that it needed replacing. The truck drove ok when cold but once warmed up,it started sputtering again under load. It didn't seem quite as bad though.

My only other idea is the fuel filter/strainer. Any ideas?

JOB1963

Kumi, any luck? I have a 1987 S10 2.8L and experience similar symptoms, not sure that we have the same sensors or ecm , your is probably a bit more advanced. Please write about your experiences, this is how we can learn from others.

Kumi

I replaced the fuel filter and it helped a little,but not much. I then replaced my fuel pump and strainer,and havent noticed any more problems. For me it was only about a $60 repair.

JOB1963

glad you found the problem, I have a few more things to check, like the electronic spark control module and have to make sure rotor is pointing to #1 cylinder when it's at top dead center. Unfortunately this chevyforum isn't very helpful. Nothing like the Ford forum where you get answers pretty quickly.

Kumi

It started sputtering out of nowhere when i left the bank,and headed to work yesterday morning. It sputtered the whole entire way,then when i drove home from work it didn't sputter at all.

I text a mechanic that i know and he said to test the ignition module. It tested fine,but it found a bunch of gunk and corrosion around it when i pulled the cap. Also some corrosion on the "points" inside the distributor cap.

Cleaned it all as best as i could last night. I drove 7 miles to my parents house,then i hauled a 266lb load of scrap with both me & my mom in the truck and it hasn't sputtered at all. I'm beginning to think it may have been the corrosion.

If it continues to do better,i'll put a new cap on it. They're only 12 bucks and it's worth it just to know that i have one less part to go bad.

JOB1963

I have a friend that told me initially to check fuel pressure, of course I blew it off thinking it had to be a sensor or vacuum leak or something, after spending close to $200 on sensors and being down for 2 weeks, I finally replaced the fuel filter. It made a significant difference, but still sputtering,(the throttle body appeared to be getting constant pressure) so then I installed an inline pressure gauge on the fuel line just for kicks and watched the pressure fluctuate. It started around 13# and then went down gradually. When engine did not start, I did the key off key on to listen for fuel pump and I heard nothing, no pressure either! after a few key on key offs, the pump ran & pressure came back but nothing consistent as is required for smooth running. So it's fuel pump/strainer today. Will post results later, hopefully good results :-)

JOB1963

You sure you have POINTS on that 91 4.3? And how did you test ignition module?

Kumi

I'm going by what they were called by the guy who mentioned checking them. Basically when i look inside the cap,there are 6 "prongs". I cleaned corrosion off each one. And i took the module to autozone and the put it on the test machine and tested it about 5 times and each time,it passed.

Since cleaning the corrosion,i've Driving it with no problems.

JOB1963

Good for you, that must have been the problem. GM phased out "points" in the mid 70's to early 80's because of the mechanical wear that took place necessitating a "tune up" every 12,000 miles. They were replaced with electronic ignitions that have no mechanical wear and tear. And of course now they had to install sensors all over the place to monitor MAP(manifold air pressure), engine vibration(KNOCK sensor), ECT engine coolant temp., TPS(throttle position sensor), ETS(engine temp. sensor) barometric pressure's measured too(not sure how or which sensor) and I'm sure I'm leaving 1 or 2 others out, but then it's all tied into the computer(ECM/PCM) which then monitors and interprets all of the points and sends a signal to the IAC(idle air control) and Fuel Injectors. I believe the EGR(exhaust gas recirculator) is actuated by the O2 sensors, not quite sure if they go through the ECM/PCM or if EGR is directly driven by O2 sensors? And then you throw in the vacuum system which ties into the PCV, air pump, MAP sensor, Vacuum reservoir, vacuum regulator, heat damper, air intake choke, purge canister, brake booster, ETS, etc...I know the vacuum affects the timing somehow just not quite sure through which sensor it works or is it a combination of sensors? I don't know it all but am always learning. Hope this helps peak someones interest.

Kumi

That's nice to know. I've been having success still,however i'm still having a problem where it sometimes wants to stall when stopping. I've been told to check for a vacuum leak,but it only happens intermittently. I'm wondering if the egr valve may be sticking.