RustyMacintosh
Well-Known Member
- Joined
- August 5, 2018
- Messages
- 190
- Reaction score
- 50
- City, State
- Monterey
- Year, Model & Trim Level
- 94 XLT 4x4 Exploder
This 94 XLT has new heads. Runs great now that we got the right head gaskets on it.
OK, interesting problem. Before the heads were replaced, there was a slight misfire in the mornings, cold. Only for maybe 20 seconds. The one cylinder that was leaking the plug was wet. The engine was consuming maybe a quart of antifreeze every other day.
Now, starts great stone cold. Starts great at operating temp. Idles smoothly. But--let it sit for 30 minutes, such as, if you drive it somewhere. Then go inside to shop, come out 30ish minutes. On startup--
Misfire. You have to sorta depress the gas pedal a bit to keep it from dying. The RPM's waver up and down. Experimenting a bit, I found that if you hold the gas pedal a bit--forcing RMP's, it will go up to about 1500, you can feel the miss-fire then all of a sudden the RPM's shoot to 2500 and runs smooth.
Like a vacuum leak just cleared up.
So I swapped out the IAC, twice. No change. I am leaning now towards the EGR. I am thinking the EGR is hanging open a bit. I've sprayed the engine for vacuum leaks to find nothing.
I am thinking of pulling the EGR valve off, OR, disconnect the vacuum lines to it, re-route the lines to a loop, so the EGR valve will stay closed. Then try it.
Ideas? Only when the engine has been warmed up than sat for 1/2 hour or more does this occur.
OK, interesting problem. Before the heads were replaced, there was a slight misfire in the mornings, cold. Only for maybe 20 seconds. The one cylinder that was leaking the plug was wet. The engine was consuming maybe a quart of antifreeze every other day.
Now, starts great stone cold. Starts great at operating temp. Idles smoothly. But--let it sit for 30 minutes, such as, if you drive it somewhere. Then go inside to shop, come out 30ish minutes. On startup--
Misfire. You have to sorta depress the gas pedal a bit to keep it from dying. The RPM's waver up and down. Experimenting a bit, I found that if you hold the gas pedal a bit--forcing RMP's, it will go up to about 1500, you can feel the miss-fire then all of a sudden the RPM's shoot to 2500 and runs smooth.
Like a vacuum leak just cleared up.
So I swapped out the IAC, twice. No change. I am leaning now towards the EGR. I am thinking the EGR is hanging open a bit. I've sprayed the engine for vacuum leaks to find nothing.
I am thinking of pulling the EGR valve off, OR, disconnect the vacuum lines to it, re-route the lines to a loop, so the EGR valve will stay closed. Then try it.
Ideas? Only when the engine has been warmed up than sat for 1/2 hour or more does this occur.
