Truck was running a little rough before valve cover gasket replacement. Replaced gaskets and it ran rougher than before. Found a burned out spark plug coil and replaced coils, plugs, and wire. Runs smoothly now, but there’s very, very low power, probably tops out at 35 mph. What gives?
Last time i had this problem it was a clogged cat.
Is there a way to clean it out or would it need to be replaced?
If you had reasonable power before you replaced gaskets you may have knocked something loose. This is a redundant statement but you should have AutoZone or someone like them check for codes and post them here . Cats are expensive so I would not just replace unless proven to be bad.
I apologize for the naive question, but are there codes to read even if there isn’t an engine light on? There was a light on prior to changing the spark plugs, but there hasn’t been one since.
"There was a light on prior to changing the spark plugs"
That is a good place to start resolving the problem.
What was the code?
Lets try this again. Did you have power before you did the work?
Engine codes were: P0171 and P0172, I believe.
I did have power before replacing the gaskets, but it was running a little rough. An oil change (after which I discovered the gasket leak) helped but didn’t remedy it. After replacing the spark plugs, coils, etc. the engine runs smooth, but there’s a significant reduction in power.
A dirty/bad Mass Airflow Sensor (MAF) could be the source of those codes and the reason for the loss of power.
Forgot to mention, the MAF was cleaned when the valves were replaced.
You mean the valve cover gaskets were replaced, right?
So it ran rough but with normal power at the higher speeds before. And the check engine light was on. Then you replaced the valve cover gaskets, changed the engine oil, and replaced the spark plugs, wires, and coils? Now it idles and runs fine at low speeds, but won’t go over 35 mph? And the check engine light it now off?
I expect the check engine light will soon come back on. Likely the battery power was removed during the fix-up. That can turn off the CEL. And it takes a certain amount of drive cycles before it comes back on. In the meantime the computer may have detected a problem and is keeping you in limp mode in order to protect the engine or transmission from some problem it thinks it may have. The best course of action – besides having a shop do a quick visual check for any obvious problems like loose or misplaced wires or vacuum components – is to use a scanner to read out the diagnostic codes. Yes, there can be stored diagnostic codes even with the CEL off.
Better quality scanners can read both active and pending codes. Pending codes are things the computer is suspicious about, but hasn’t yet made up its mind.
In the meantime the computer may have detected a problem and is keeping you in limp mode in order to protect the engine or transmission from some problem it thinks it may have.
Disconnecting the battery will clear the codes and also turn off the limp-mode (if it was on). I’ve never seen limp-mode present without a CEL light…but it’s possible…and sure sounds like it.
My suspicion is something got knocked loose or not reconnected during the vale-cover replacement.
“My suspicion is something got knocked loose or not reconnected during the vale-cover replacement.”
+1
Is this a V6 engine and if so, does the intake manifold, or part of it have to be remove to remove the valve covers?
Is this a V6 engine and if so, does the intake manifold, or part of it have to be remove to remove the valve covers?
What engine requires the intake manifold be remove to remove the valve covers. Not even sure how that would be designed.
Head gasket - MAYBE.
Sure wish ARI would tell us …WHAT truck ?
We have lots of vehicles that the intake…plenum…has to come off for valve cover gasket replacement .
We have lots of vehicles that the intake..plenum...has to come off for valve cover gasket replacement .
Never seen a design like that.
there u go. Intake has to come off for valve cover job
Never seen a design like that.
I think just about any V6 Honda Odyssey or Accord, Toyota Camry or Avalon, Lexus ES or RX Series, Ford Taurus from 85-07, and many many others.
It is necessary to remove the upper intake manifold to remove both valve covers on most Toyota V-6 engines, on some engines one valve cover can be removed with the manifold in place.
The valve covers can be removed on the V-8 with the manifold in place.