Engine runs rough between 2k and 3krpm only

cody_321 · 03-25-2007, 08:07 PM

I will be running down the highway at 70mph between 2 and 3000rpms and i will try to accelerate to pass another car or go up a hill and the engine bucks and snorts (no backfire) i've checked all of the plugs and they are fine. any suggestions on what could be wrong?

75K30 · 03-25-2007, 08:28 PM

Timing control is, how should I put this,,,,,jacked. Allright it could be other things, but we may need to know what type of chev truck you have. A truck with a carb and a points ignition may have different things to look at than say one that is injected, and has multiple coil packs.

cody_321 · 03-25-2007, 08:38 PM

it's a 1993 Chevy c1500 4.3 tbi w/ manual tranny

junior3382 · 03-25-2007, 09:16 PM

I had a similar engine in my '95 S10, when was the last time you had the timming belt/chain checked? 75K30 is right, it sounds like a timming issue, unless you clutch is slipping, but it doesn't sound like a slippage problem. In that engine I would also check the ignition coil. But it could also be a carbon build up. Check the throttle body to see if it is clean, and spraying fuel properly. I wish I could help more, but unfortunatly, regardless of how much I beat the **** out of my truck, I never had any power issues.... sorry. I hope any of this helps.

75K30 · 03-25-2007, 09:34 PM

How does it run at this rpm at lower speeds? If you were to slow down and run the rpm, does it do the same thing?
The most obvious would be electrical, like the cap, and rotor button. However I would imagine a missfire might result in a backfire, and you said it does not do that.
Another option might be fuel pressure, if it is too low, it may not be able to meet the demands of the engine at higher speeds. This could come from a bad regulator, I believe it is located right on the side of your TB.
The other item might be a clogged exhaust system. Have seen some clogged systems that do not run hot, and change performance considerably. I use a gauge with an O2 sensor adapter, iI install this gauge in place of any O2 sensor, ang rev the engine, I like to see pressures lower than 3psi, anything higher will prove to be a blocked exhaust.
Some might say the PCM may need to be reflashed, but this might be a last resort. This is a tough issue, and unfortunately there is not a one sentance answer, we can just try to share ideas, and hope that in time one of them works out.....

junior3382 · 03-25-2007, 09:49 PM

You know, 75K30 is right, I would check the exhaust. A buddy of mine had an old Caprice w/a 305 and the converter was clogged from age, and even though it did not turn red either, it cause high speed bogging. Not sure why i didn't think of that too. And it wouldn't backfire if that was the problem, I would definitely consider the possibility anyways.

cody_321 · 03-25-2007, 10:14 PM

when i bought the truck it came w/ detailed logs of what the owner had done before. and it said that a whole new dist. rotor and cap was installed only like 13k miles ago so i don't think it would be that and all of the spark plugs looked like they were firing right, all the gaps were good. there was a whole new transmission installed about 30k miles ago so i don't think it would be the clutch, which is what i was thinking when it first started. i've run 3 bottles of injector cleaner through the system 2 bottles w/ a full tank and this last fill of gas just 1 bottle. i was thinking the solenoid, but that wouldn't be because all of the plugs are firing. where could i find the right thing to do the pressure check on the exhaust?

junior3382 · 03-25-2007, 11:48 PM

Okay, to check your exhaust, this is kinda tricky. Only a few shops have the equipment to do it, and you would have to call around to find them for sure.... However, most of the guys here will tell you to get the motor warmed up nice, either running to the store or whatever, then when you come home, while it is running get under the truck and the converter should be red if the clog is bad enough. Works better at night...lol. However, that will only work if the clog is bad, sometimes it is just restricted enoguh to cause a head ache, if you can't find a grage to check it, the next best way is to detach the converter. Yes the truck will be extremely loud, but its only temp. Then take it out for a spin, if the converter is restricting your flow, when you remove it you will notice an immediate power increase. now no back pressure will give more boost naturally, so I would try to simulate the very driving condition it bogs down during. If it goes away, there is your problem, if not, then that wasn't it, re-connect it and then thats eliminated. I know this is kinda the red-neck way to diagnose this problem, but its fun as well as useful, especially if you like loud motors! lol. Anyways, that what I would do.

cody_321 · 03-26-2007, 05:16 PM

well it turns out that the only thing that was wrong with the truck was a single bad plug wire. i took it on the #1 plug wire off the dist. and about a spoon full of corroded metal and dirt fell out and replaced all new plugs and it runs fine now. thanks for all the advice!

junior3382 · 03-26-2007, 05:41 PM

well, I am glad it was a simple fix. We all would have suggested that however, you mentioned you checked them. That was definitely the cheapest fix. Good luck to ya, glad your truck is good now....

03-25-2007, 09:16 PM	#4
junior3382 Senior Member Join Date: Mar 2007 Location: Currently, I live in Lancaster county, Pennsylvania. Posts: 3,170	I had a similar engine in my '95 S10, when was the last time you had the timming belt/chain checked? 75K30 is right, it sounds like a timming issue, unless you clutch is slipping, but it doesn't sound like a slippage problem. In that engine I would also check the ignition coil. But it could also be a carbon build up. Check the throttle body to see if it is clean, and spraying fuel properly. I wish I could help more, but unfortunatly, regardless of how much I beat the ** out of my truck, I never had any power issues.... sorry. I hope any of this helps. __________________ The Blazer is dead, so I pumped her with lead, laid her to bed, and bought a FORD instead!**

03-25-2007, 09:49 PM	#6
junior3382 Senior Member Join Date: Mar 2007 Location: Currently, I live in Lancaster county, Pennsylvania. Posts: 3,170	You know, 75K30 is right, I would check the exhaust. A buddy of mine had an old Caprice w/a 305 and the converter was clogged from age, and even though it did not turn red either, it cause high speed bogging. Not sure why i didn't think of that too. And it wouldn't backfire if that was the problem, I would definitely consider the possibility anyways. __________________ *The Blazer is dead, so I pumped her with lead, laid her to bed, and bought a FORD instead!*

03-25-2007, 11:48 PM	#8
junior3382 Senior Member Join Date: Mar 2007 Location: Currently, I live in Lancaster county, Pennsylvania. Posts: 3,170	Okay, to check your exhaust, this is kinda tricky. Only a few shops have the equipment to do it, and you would have to call around to find them for sure.... However, most of the guys here will tell you to get the motor warmed up nice, either running to the store or whatever, then when you come home, while it is running get under the truck and the converter should be red if the clog is bad enough. Works better at night...lol. However, that will only work if the clog is bad, sometimes it is just restricted enoguh to cause a head ache, if you can't find a grage to check it, the next best way is to detach the converter. Yes the truck will be extremely loud, but its only temp. Then take it out for a spin, if the converter is restricting your flow, when you remove it you will notice an immediate power increase. now no back pressure will give more boost naturally, so I would try to simulate the very driving condition it bogs down during. If it goes away, there is your problem, if not, then that wasn't it, re-connect it and then thats eliminated. I know this is kinda the red-neck way to diagnose this problem, but its fun as well as useful, especially if you like loud motors! lol. Anyways, that what I would do. __________________ *The Blazer is dead, so I pumped her with lead, laid her to bed, and bought a FORD instead!*

03-26-2007, 05:41 PM	#10
junior3382 Senior Member Join Date: Mar 2007 Location: Currently, I live in Lancaster county, Pennsylvania. Posts: 3,170	well, I am glad it was a simple fix. We all would have suggested that however, you mentioned you checked them. That was definitely the cheapest fix. Good luck to ya, glad your truck is good now.... __________________ *The Blazer is dead, so I pumped her with lead, laid her to bed, and bought a FORD instead!*

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03-25-2007, 08:07 PM	#1
cody_321 Full Member Join Date: Feb 2007 Location: home town is columbia, mo but for right now Mcpherson, Ks Posts: 18	Engine runs rough between 2k and 3krpm only I will be running down the highway at 70mph between 2 and 3000rpms and i will try to accelerate to pass another car or go up a hill and the engine bucks and snorts (no backfire) i've checked all of the plugs and they are fine. any suggestions on what could be wrong?

03-25-2007, 08:28 PM	#2
75K30 Senior Member Join Date: Jul 2006 Posts: 3,312	Timing control is, how should I put this,,,,,jacked. Allright it could be other things, but we may need to know what type of chev truck you have. A truck with a carb and a points ignition may have different things to look at than say one that is injected, and has multiple coil packs.

03-25-2007, 08:38 PM	#3
cody_321 Full Member Join Date: Feb 2007 Location: home town is columbia, mo but for right now Mcpherson, Ks Posts: 18	it's a 1993 Chevy c1500 4.3 tbi w/ manual tranny

03-25-2007, 09:34 PM	#5
75K30 Senior Member Join Date: Jul 2006 Posts: 3,312	How does it run at this rpm at lower speeds? If you were to slow down and run the rpm, does it do the same thing? The most obvious would be electrical, like the cap, and rotor button. However I would imagine a missfire might result in a backfire, and you said it does not do that. Another option might be fuel pressure, if it is too low, it may not be able to meet the demands of the engine at higher speeds. This could come from a bad regulator, I believe it is located right on the side of your TB. The other item might be a clogged exhaust system. Have seen some clogged systems that do not run hot, and change performance considerably. I use a gauge with an O2 sensor adapter, iI install this gauge in place of any O2 sensor, ang rev the engine, I like to see pressures lower than 3psi, anything higher will prove to be a blocked exhaust. Some might say the PCM may need to be reflashed, but this might be a last resort. This is a tough issue, and unfortunately there is not a one sentance answer, we can just try to share ideas, and hope that in time one of them works out.....

03-25-2007, 10:14 PM	#7
cody_321 Full Member Join Date: Feb 2007 Location: home town is columbia, mo but for right now Mcpherson, Ks Posts: 18	when i bought the truck it came w/ detailed logs of what the owner had done before. and it said that a whole new dist. rotor and cap was installed only like 13k miles ago so i don't think it would be that and all of the spark plugs looked like they were firing right, all the gaps were good. there was a whole new transmission installed about 30k miles ago so i don't think it would be the clutch, which is what i was thinking when it first started. i've run 3 bottles of injector cleaner through the system 2 bottles w/ a full tank and this last fill of gas just 1 bottle. i was thinking the solenoid, but that wouldn't be because all of the plugs are firing. where could i find the right thing to do the pressure check on the exhaust?

03-26-2007, 05:16 PM	#9
cody_321 Full Member Join Date: Feb 2007 Location: home town is columbia, mo but for right now Mcpherson, Ks Posts: 18	well it turns out that the only thing that was wrong with the truck was a single bad plug wire. i took it on the #1 plug wire off the dist. and about a spoon full of corroded metal and dirt fell out and replaced all new plugs and it runs fine now. thanks for all the advice!