sputtering at cruising speeds

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?

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)

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

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 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

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

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

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

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

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

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

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?

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

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...

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

have you run a diagnostic on it? I have been working on my 99' k1500 the past 2 days because mine is sputtering and mine is because my 3 and 7 arent firing I dont know whats wrong yet but ill let you know if i figure anything out

i'm carrying the truck to my friends shop within the next few days to hook it up to his cpu to monitor the injectors and determin wether the injector is bad, or the computer is bad, ill update once i figure this out... i might add tho the injectors are both new, so i dont think its an injector problem but if it is a cpu prob, if i have to get a new one does anyone know what this might cost me?

i would say check aftermarket magazines and not magazines for exhaust and intake, a true engine magazine rather than going to a dealer and paying out the rear for the same thing you might find a better deal for an aftermarket that could make some more power and probably cheaper, I dont know for sure never done it but a friend back home did it...

ill have to check into that if it comes down to having to get a new cpu, ill post again as soon as i find whats wrong

well checked 2 see if the cpu was bad... its good sending the right signal to both injectors... replaced the "dripping" injector cause it was still under waranty... no more dripping but im still gettin the miss after the motor warms up.... im goin back 2 my friends shop 2moro and were gonna test the plugs, plug wires, n all that stuff 2 see if that might be the problem, ill update as soon as we figure it out

Take a look at this: http://www.mightyautoparts.com/pdf/articles/tt71.pdf

The pickup coil fixed my miss when warm.

//2000CAYukon

thanks for your help man but on that article its talkin about the chevy 5.0's and 5.7's and mines a 4.3 V6, im gonna carry my truck back to my friends shop and if it comes down to it we will pull the dist. and replace the pick-up coil.. who knows that could be it... ill update later when i figre it out

thanks for your help man but on that article its talkin about the chevy 5.0's and 5.7's and mines a 4.3 V6, im gonna carry my truck back to my friends shop and if it comes down to it we will pull the dist. and replace the pick-up coil.. who knows that could be it... ill update later when i figre it out

True that the article was for the 5.0/5.7 but the dist and pickup coil work the same way for the v6.

At least try to get a reading of from the pickup coil. In my case, I decided to pull the dist looking for wear. The plastic on the pickup coil has cracked and the coil was pretty rusty. Cost was only $20 at my local AC Delco parts store.

Also, if you do pull the dist, make sure the magnet and the shaft look good. If the magnet can move on the shaft, you will need a new shaft.

Also, if your dist is original, the pickup coil is 14 years old!

Good luck and let us know how is goes.

//2000CAYukon

i talked 2 my friend today about takin my truck to his shop, im gonna take it tomorrow n hes gonna test the pick-up coil and the ignition control module, also last time this happened it ended up being a blown head gasket.. i HIGHLY doubt this will be the case again but for everyone else reading this if you've checked EVERYTHING, be sure you check compression on all cylinders one at a time with ALL spark plugs out, last time i checked it i left the other plugs in and found no prob but when the mechanic did it and pulled the plug next to the one he was checkin the pressure dropped, but i really doubt this will be the case again both heads have been rebuilt and brand new head gaskets but then again who knows? ill update again tomorrow after i figure out what the problem really is..

well after having a huge problem with advanced autos giving me a second new injector cause the other one started dripping and then them giving me the wrong one... i put my old stock ones back in (even tho a few months back they werent even spraying) i figured id give it a shot, and they spray like new now and the truck isnt missin nemore, so it was the injector, if you EVER buy injectors dont go to advanced autos, my friend told me if i ever got new ones get performance ones with a waranty or get AC Delco's so itll be like stock new, it was only 6 or 7 months and the ones i had from advanced went bad, and now i put in some that are 14 years old and they work? hmm.. well the prob seems to be fixxed for now.. if i find out its not ill let yall know but i believe it is

well spoke to soon, STILL having the SAME problem, and NEITHER injector is dripping, problem ONLY occurs when cruising normally and about the time the shift light comes on, during acceleration its real smooth and deceleration is smooth too, its when the speed levels out and im about to shift.. whats goin to be crazy is when it IS the pick-up coil like 2000CA said, i'll let yall know when i get this figured out

well spoke to soon, STILL having the SAME problem, and NEITHER injector is dripping, problem ONLY occurs when cruising normally and about the time the shift light comes on, during acceleration its real smooth and deceleration is smooth too, its when the speed levels out and im about to shift.. whats goin to be crazy is when it IS the pick-up coil like 2000CA said, i'll let yall know when i get this figured out

I am now wondering if you have a Torque Converter Clutch (TCC) lock up problem. When the problem is happening, tap the brake pedal. Just tap it since that should unlock the TCC. Does it always happen at the same engine RPM? If so, put the tranny is 2nd and get the engine to the same RPM and see if the problem occurs.

Normally, the TCC locks up after 40 MPH depending on throttle position. You could also drive the truck in D instead of OD to see if you can still recreate the problem. I am pretty sure that the TCC does not lockup in D (but not 100% sure).

If the pickup coil was giving you problem, it would surely show up at idle and lower RPM.

//2000CAYukon

i got a manual trans, and at idle there is somewhat of a miss, and sometimes at lower RPM's but when im driving and about to shift its very notacable

i got a manual trans, and at idle there is somewhat of a miss, and sometimes at lower RPM's but when im driving and about to shift its very notacable

OK. That rules out the TCC :biggrin:

Pickup coil is still a possibility. I also wonder if the fuel pressure regulator is bad causing the fuel pressure to change while you are cruising.

//2000CAYukon

yea i also wondered about the pressure regulator.. ill check all this out

yea i also wondered about the pressure regulator.. ill check all this out

Unfortunately, the TBI trucks do not have a test port for hooking up a fuel pressure tester. There is a tool that goes where the fuel filter is to give you a test port. Then you need a long hose with a gauge so that you can look at it while you are driving.

Otherwise, the fuel pressure regulator is in the back of the TBI unit.

//2000CAYukon

I just solved this on mine. Truck had the incorrect EGR valve and the EGR restrictor was not installed. There also was issue with the Throttle body base gasket having a small blow through. So small infact that it took 5 tries to find it and 2 seperate attempts at getting a proper seal. Final gasket used was a felpro that was thicker than both the stock and rebuild gaskets. Gasket had to be sprayed with red gasket tack for proper seal. Disconnected the batt for 30 mins, reset everything and no more studder at part throttle.

well if its the EGR, would undoing the vacuum line that runs to it stop the miss? cause a while back i did that and it still continued, also tested for leaks around throttle body by spraying carb cleaner around the base and there was no change at idle? so i do not believe there is a leak. i don't want to purchase a new EGR valve unless i know for sure thats it because there $40, and not to far back the EGR valve solenoid was replaced. So is there any way to test and see if its for sure the valve?

ok i checked my EGR and it opens and closes freely, so its good? does anyone know somewhere i could take my truck where they could test my ignition system and tell me whether its that or a fuel problem?

well if its the EGR, would undoing the vacuum line that runs to it stop the miss? cause a while back i did that and it still continued, also tested for leaks around throttle body by spraying carb cleaner around the base and there was no change at idle? so i do not believe there is a leak. i don't want to purchase a new EGR valve unless i know for sure thats it because there $40, and not to far back the EGR valve solenoid was replaced. So is there any way to test and see if its for sure the valve?

Throttle body base gasket having a small blow through. So small infact that it took 5 tries to find it and 2 seperate attempts at getting a proper seal. Final gasket used was a felpro that was thicker than both the stock and rebuild gaskets. Gasket had to be sprayed with red gasket tack for proper seal. Disconnected the batt for 30 mins, reset everything and no more studder at part throttle.

Also, which EGR does your truck have, there are 2 different types. Both require and restrictor to be installed and staked into the valve. Also your valve may be good, and your passages may be clogged.

hell i dont know what kind it is, its got one vacuum hose connected to it and the haynes manual says all u do is bolt it on n hook up the vacuum? and ive checked every vacuum line n there all good..

hell i dont know what kind it is, its got one vacuum hose connected to it and the haynes manual says all u do is bolt it on n hook up the vacuum? and ive checked every vacuum line n there all good..

Does it have a silver top or a gold top? Do you know if was ever replaced? What is the number from the original egr valve? Included with the new EGR valve will be a sheet that has a list of numbers and their corrosponding restrictor sizes listed with instructions on how to properly install it. Haynes is not a good manual if you dont know alot about cars. They assume a certain amount of information is already known. Find a local autoparts store that has a retired mechanic working there, this alone will help out, espcially if you can become freinds with him in an apprenticeship sort of way.

we had another 4.3 put in a year back because my old one burnt oil bad, its ran for a year fine? so if it was the wrong EGR wouldnt it have does this before? I still have my EGR off my old motor its still attatched to my old intake manifold and it does look different than the one on the motor now, the one on my old manifold is black and is a bit smaller, the one on my motor now is grey and is a bit bulkier than the black one, but like i said its ran for a year no problem? so i dont think this could be it? and if it was, unhooking it would have stopped the miss? atleast temperarily?

well looks like its going to be either a burnt valve or a head gasket, put in new dist. due to the fact that the old one was rusted n had a small crack, now the miss is real steady, the guy that looked at it said it was prolly more than one problem and puttin in the new dist. helped but still didnt completely fix it, hes gonna do a compression check on it and try to adjust the valves to see what he can get it to do, its not so much of a miss anymore its like the engine compression is off on a few cylinders cause the engine itself runs fairly smooth theres just some vibration and it gets real rough when driving it JUST like before when my head gasket blew, ill keep you informed on my success, also may i add i got a rebiuld kit for my TBI and rebuilt it with new seals ext.. also put in my original injectors, and no injector is dripping now but engine is still running bad and getting worse everyday

update... fixxed tons of problems but nothing changed the missing prob, it varies so much its hard to figure out sometimes it acts like its fuel other times it acts like a miss on a plug, starter cable was loose, tightened it, compression check was ok and valves seem ok, said it might be a lose wire grounding out somewhere sooo new project tomorow, ima check all my stereo wiring and fog light wiring and also check for lose stock wires that might be grounding out or something to that nature, if not i dunno what its gonna be, thank all of yall for helpin me out i appreciate it

Freaking great. I'm having the exact same problem with my truck - 1998 k1500 5.7L. I'm about to lose it. I took it in to have the codes read - random missing cylinder. However, it is precisely three cylinders - 4, 5, 7. I pulled the plugs from these cylinders to check for cracks, etc. All three are fairly fouled - I installed the plugs less than 1000 miles agos, along with new wires, cap, rotor. Please help if anybody has any input.

Thanks,
sivadnar

well i pulled half the truck appart checking for loose grounds and wires, found a few loose connections it seemed but miss is still occuring, talked to another friend of mine that was having this problem with his brand new f150 and it ended up bein the fuel pump, i was told the best thing to do would be find some1 with a full diagnostics computer and have them run a complete diagnostics on it to find out the exact problem, and if i didnt want to spend that money just drive it untill whatever it is gives out completely, also asked about checkin fuel pressure but its so hard on my truck cause u gotta buy an adapter to go where the fuel filter is and was also told even if the pump is bad whatever is happening could happen so quick the fuel pressure gauge may not even read a change

well i drove my truck around some today n ive got the worse gas millage ever, drove maybe 10 miles and it used 1/8 of a tank of gas, no more than 40 MPH too, i plan to take it 2moro for a diagnostics but i got a good feelin its gonna be my fuel pump

Keep 'em coming Wally. I broke down and took my heap into a shop for an official diagnosis. I swear my truck has the exact same symptoms as yours. I'll post the official...

Forget the EGR; once your off-idle and up above 2,000rpm or so, you could have a monster size leak in the EGR and wouldn't do what your truck is doing. It sounds like you have been thru all of the ignition system, assuming the new ditributor had a new pickup, etc. on it. I know this sounds stupid, but have you changed the fuel filter recently. If so, I think you sohuld focus on the fuel pressure regulator,the fuel pump, and the relay. I have been told that the relay can be "weak" and not go out all of the way, but cause driveability issues. All of my experience is with small block v8's, but they are exactly the same as your 4.3. You just have 2 cylinders lopped off the front! Good luck, I really think your problem (if not an internal engine problem) is fuel delivery related.

yea its definately not ignition, ima have my fuel pressure checked to see if its the pump, i got a new pressure regulator and i know its not my injectors, if the pressure jumps or is off ill put in a relay first to be sure and then if that dont work a pump? thanks

The shop said they think it is my fuel pump and/or fuel injectors. The fuel pressure supplied by the pump is approximately 50 psi and specs are 60-65 psi. Would this difference really make my truck sputter at cruising speeds?

Thanks,
sivadnar

The shop said they think it is my fuel pump and/or fuel injectors. The fuel pressure supplied by the pump is approximately 50 psi and specs are 60-65 psi. Would this difference really make my truck sputter at cruising speeds?

Thanks,
sivadnar

Sivadnar,
What year is your truck? Must be 96 or newer with the specs you listed. The TBI Trucks (87-95) have a lower pressure which is 9-13 PSI.

//2000CAYukon

i just went and got a fuel pump and filter, plan to put it on within the next few days, ill post and say if that fixxes it or not

ok yall, new pump, strainer, filter, relay, STILL RUNNING BAD, its gotten to the point now where the idle isnt smooth and its still spudderin when i go down the road, ima carry it later n get a full computer diagnostics done on it. do yall think my computer has gone bad? everything i mean EVERYTHING else has been checked and/or replaced

My truck is a '98.

I installed a fuel pump this weekend too, to no avail.

I have done the following in this order;
Fuel Treatment
Fuel Filter
Plugs & Wires
Cap & Rotor
Fuel Pump
Fuel Treatment

Wally, I took my truck to an actual mechanic to get a "full diagnosis." They told me it was likely my fuel pump; but they could not be certain because the problem is intermittent.

Just to further describe my problem, which sounds the same as Wally's:
Upon reaching 65-70 mph going uphill with AC on, my truck will sputter significantly. If I hammer the pedal, the truck will level out until returning to OD then it will do it again.

It does not seem to do this if the AC is off and I'm just cruising.

I'm done screwing with. I'll be selling my truck very soon. Please post if you have any last minute ideas!

Thanks for all of the help.

Cheers,
sivadnar

My truck is a '98.

I installed a fuel pump this weekend too, to no avail.

I have done the following in this order;
Fuel Treatment
Fuel Filter
Plugs & Wires
Cap & Rotor
Fuel Pump
Fuel Treatment

Wally, I took my truck to an actual mechanic to get a "full diagnosis." They told me it was likely my fuel pump; but they could not be certain because the problem is intermittent.

Just to further describe my problem, which sounds the same as Wally's:
Upon reaching 65-70 mph going uphill with AC on, my truck will sputter significantly. If I hammer the pedal, the truck will level out until returning to OD then it will do it again.

It does not seem to do this if the AC is off and I'm just cruising.

I'm done screwing with. I'll be selling my truck very soon. Please post if you have any last minute ideas!

Thanks for all of the help.

Cheers,
sivadnar

I don't remember if you said this problem occurs hot or cold, or all the time. The only other thing I could think to check would be the catalytic convertor. It could be blocked or partially blocked causing a stall when the backpressure gets to high (hard pedal applied).

haha i give all of yall permision to shoot me....... and to every1 who is having this problem... CHECK YOUR WIRES..... my #6 plug wire was BAD i had a scope done and it told me.. i feel stupid now.. so CHECK YOUR WIRES lol... also just because the wires are brand new dont mean one is still not bad... take one u KNOW is good and swap it out with the others one by one and see if this solves your prob.. or just do what i did and go have a "scope" done.. cost me $60 but i guess it woulda been worth it in the begining after replacing everything i have replaced...

I was just about to post that you have a bad ign wire but i see that you found it. Next time take a small plastic spray bottle and fill it with water and mist the wires with that water you will see any bad wires because of the little sparks that you will see
as a gm tech i have see that problem a billion times

yea the spray bottle is a good idea i havnt heard that be4... i checked my wires n they had all LOOKED good and they were ONLY 3 weeks old.... AC Delco's too.. so i figured they were good... but i got it fixxed.. truck runs like new now so its all good