sputtering at cruising speeds

[wally91vhevrolet]

aight.. i got a 91 silverado 4.3 v6 manual trans... when i drive around n let my truck get up to temp, at cruising speeds (40-50 mph) or really any other steady speed it starts sputtering... the truck idles great and accelerates great... sometimes sputters during deceleration, could this be my EGR valve sticking? that is the ONLY thing as far as emissions are concerned that hasnot been replaced in the past year. If not what else could it be? I replaced the EGR valve solenoid a few months back... so what might be causing this? I have a flowmaster so i can hear every fault in the engine if there is one... and when it does this there is kind of a backfire? not too loud but subtle.. and also since i have a man trans i can feel it.. what should i do?

[ProjectXC]

LoL, i had the same problem with my 95' yukon, check to see if all your spark plugs are getting spark maybe its a distributor cap, wire, or spark plug, i replaced everything one day and the problem went away, on my 99' chevy I had the problem again and it was just the #5 not firing because the spark plug had loosened up because of the temperature changes in alaska(the yukon was in california)

[2000CAYukon]

Usually with a bad egr, there will be a hesitation off idle. If you are cruising at part throttle, then it could be EGR. Try plugging the vacuum line to the EGR and see if the problem goes away.

Since you have a TBI engine, it could be any of the following:
1) Worn dist staft housing
2) Pick up coil
3) TBI Gasket (spray TB cleaner around base to look for leak)
4) Leaking injector
5) Vacuum leak

//2000CAYukon

[wally91vhevrolet]

The injectors are brand new i put 2 new ones in a couple of months back, ill check the throttle body for a leak, already checked for a vacuum leak i couldnt find one, i got a new coil, dist cap n plugs n plug wires r all good....

[2000CAYukon]

Originally Posted by wally91vhevrolet

The injectors are brand new i put 2 new ones in a couple of months back, ill check the throttle body for a leak, already checked for a vacuum leak i couldnt find one, i got a new coil, dist cap n plugs n plug wires r all good....

The "Pickup coil" is inside the dist and the dist has to be removed to replace it. On my 90 K1500, I had a miss at low speeds and this was my problem. Gas mileage also went from 11 to 14 after replacing it.

//2000CAYukon

[wally91vhevrolet]

ill look at that next and prolly pick up a new one, ill tell you if it worked, looked it up and there $10 at advanced, thanks for your help man

[2000CAYukon]

Originally Posted by wally91vhevrolet

ill look at that next and prolly pick up a new one, ill tell you if it worked, looked it up and there $10 at advanced, thanks for your help man

I should also point out that with a timing light on the truck at idle, I could see the miss with the light.

//2000CAYukon

[wally91vhevrolet]

the truck has a real smooth idle, im pretty sure theres no miss then, i really paid attention to it today when i was drivin it, and it only happens when the rpms are at or above 2000 (just a guess i have no tach), and also it happens the most during slight acceleration, when the speed levels out its not as noticable or it doesnt happen as much, also only happens when the truck is up to temp, not when its cold

[2000CAYukon]

Originally Posted by wally91vhevrolet

the truck has a real smooth idle, im pretty sure theres no miss then, i really paid attention to it today when i was drivin it, and it only happens when the rpms are at or above 2000 (just a guess i have no tach), and also it happens the most during slight acceleration, when the speed levels out its not as noticable or it doesnt happen as much, also only happens when the truck is up to temp, not when its cold

This is sounding more like the EGR to me than the pickup coil. For me the miss was present both warm and cold. It was more noticeable warm since the idle was lower.

Have you tried plugging the vacuum hose to the EGR valve (just to see if the problem changes)?

I would also suggest checking the fuel pressure but there is no service port on the fuel rail. Replace fuel filter if is has bee a while.

I had an EGR valve go out on my 96 Impala SS. When the engine was warm, the idle would get rough and I would get a hesitation off idle until the engine got to 1500 or 2000 RPM.

Good luck.

//2000CAYukon

[wally91vhevrolet]

thanks for your help man, ima plug the vacum to the EGR tomorrow and see if that works, if not it might be the fuel pressure regulator, i didnt replace that when i put in new injectors

[2000CAYukon]

This is out of a 90 FSM. Hope it helps:


SURGES AND/OR CHUGGLE
Definition: Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down with no change in the accelerator pedal.

Use a "Scan" tool to make sure reading of VSS matches vehicle speedometer. See Code 24 in SECTION 3.
CHECK:
- For intermittent EGR at idle. See SECTION 9.
- Ignition timing. See "Vehicle Emission Control Information" label.
- Inline fuel filter for dirt or restriction. See CHART A-6 in SECTION 3.
- Fuel pressure. See CHART A-6 in SECTION 3.
- Generator output voltage. Repair, if less than 9 volts or more than 16 volts.
- TCC Operation. See SECTION 10.
Inspect Oxygen sensor for silicon contamination from fuel, or use of improper RTV sealant. The sensor may have a white, powdery coating and result in a high but false signal voltage (rich exhaust indication). The ECM will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
Remove spark plugs. Check for cracks, wear, improper gap, burned electrodes, or heavy deposits. Also, check condition of distributor cap, rotor, and spark plug wires.

//2000CAYukon

[wally91vhevrolet]

i unplugged the EGR, still continued, now its doing it somewhat at idle, im hearing somewhat of a ticking noice around my Dist. cap, ima check that out next for maybe a loose rotory button, or if not that cause its new anyway, i guess it would be the pick-up coil?

[2000CAYukon]

Originally Posted by wally91vhevrolet

i unplugged the EGR, still continued, now its doing it somewhat at idle, im hearing somewhat of a ticking noice around my Dist. cap, ima check that out next for maybe a loose rotory button, or if not that cause its new anyway, i guess it would be the pick-up coil?

It can also be a worn dist shaft or housing. If you can move the rotor side to side, then the shaft or housing is worn.

After reading many posts in this forum, I decided to pull the dist and check for wear. The shaft and housing was fine, so I replaced the pickup coil. The pickup coil tells the ignition module when the rotor position is aligned with one of the plug wires. Similar to how points worked in the old days.

Also on my mine, the plastic around the pickup coil was cracked but you can't see that unless you disassemble the dist because of the shield over the pickup coil.

//2000CAYukon

[wally91vhevrolet]

well problem STILL not fixxed, checked everything cap rotor ect., the right injector is dripping a little, could this be it? gas builds up around it and drips, but its still sprays like the other just leaks a little? could this be my problem? would injector cleaner fix this? the injectors are new... maybe 6 months old? could it be the fuel pressure regulator cause i never replaced that...

[ProjectXC]

heh, you've got "the drip" and no thats not a good thing, because if it is dripping between sprays then that cylinder would be running rich because of more fuel and the air is still being injected at the same rate so the burn isnt complete or any at all, I use to be a firefighter so in my opinion that doesnt sound good