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I have a 1989 Chevy Silverado 4x4 with a 454 and a 4sp manual transmission. It supposedly has low miles on it and ran great up until recently.
A few weeks ago it started running rough when I try to accelerate and the RPMs are low, but once the RPMs are up a little bit, it smooths out and runs fine. Now it's gotten a lot worse. When I start off in first gear, I can rev it up a little bit and it's fine, but shifting to 2nd it shakes and hesitates in the lower RPM range. Once I'm up past 2500 or so, it accelerates fine. A previous car I had had this same problem and it was the spark plug wires. I was told that it could be fuel filter related, but a restricted filter would seem to me to cause more problem as fuel consumption increases, i.e. high RPMs. I ran the engine at night looking for arcing but didn't see any.
Answer -
Hi Jim,
I agree with you...fuel filter would idle ok, but loose when power is needed.
EGR valve comes to mind, as well as throttle position sensor.
I sure did have one though, that idled ok, but was real doggy trying to take off, but ran fair...just didn't want to accelerate. It was a split hose inside the gas tank, causing low fuel pressure. I'd stick a test gauge on it and make sure there is at least 12 PSI while running.
Van
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Hi Van,
Well I tried replacing the EGR valve. It didn't fix the problem. It might be a little better at the really low RPM with partial throttle, but if I push down more than 25%, it really chokes. It almost seems like it has a little more power at the good points though, so maybe it was part of the problem?
Now it seems to have more of a defined sputter area, like when I'm cruising along, I can find a spot in the throttle where it just sputters and wants to die. I think anything above that spot is bad.
Oh, and I checked the throttle position sensor following the directions in my chilton manual and that checks out okay.
When I go to fill up with gas and remove the cap, there's always a lot of pressure coming out of the tank, and it has 2 tanks, so I'm guessing that's not the problem.
Would you think spark plug wires might be a good next step? They don't look that bad, and they have heavy duty boots, so I'd rather not replace them if that's not the problem.
Thanks a bunch for the help.
-Jim
Answer -
Hi Jim,
On that pressure you say is in the tank...next time, check closely, and see if it is really pressure, or if a vacuum is forming in the tank....Can starve the engine.
I have a Olds with a V6, that had a broken valve spring, and it would shudder when it shifted into OD, but ran good under lighter load and higher RPM.
So have you checked the pressure yet?
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I checked and I can't tell. I can hear the air when I remove the cap, but it's really hard to tell if it's coming or going. But it's been doing that since I got it, when it wasn't having problems. Also, it's doing it with both tanks and when they're full or empty.
And, I replaced the spark plug wires today, and I still have a problem. I'm not sure if the symptoms are exactly the same now or not. When I took it for a test drive, the first 25% of throttle seems to work okay and have plenty of power, but beyond that it sputters and chokes a lot. Even when I'm cruising along going pretty quick, if I try to put my foot into it a little bit, it just chokes and sputters and when I let up it's fine. I was thinking that it almost seems like fuel filter now, so I might try replacing that tomorrow, unless you have any other ideas. I don't have a guage to check the fuel pressure and wouldn't know where to check it (I didn't see any port to hook one up to.)
Also, my EGR valve, it has a separate EGR solenoid I think it is. Any chance that could be causing a problem?
Thanks
-Jim
AnswerHi Jim,
On the fuel filter question, yes, that could cause it to starve. The pressure check could verify that.
I had to get an adapter that goes right in the location of the fuel filter for that range of trucks. I really don't like it, though, because if the filter is dirty, means there is dirt in the system, and that adapter runs the vehicle without a filter, which I don't like.
As for the tanks...if it is vacuum, you won't smell the gas fumes as strong as if it is blowing out pressure.
But if the tank vent system isn't working, it could effect both tanks.
That egr solenoid controls the vacuum to the egr valve. You could disconnect and plug the vacuum hose temporarily to see if it runs better without it connected, which will verify weather egr is the problem.
It is sure sounding like low fuel supply.
Some parts houses will loan testers for a deposit, if you buy replacement parts from them.
Van
