Misfire / hesitation only when warm.

[hkerekes]

I have had a few issues with this truck that I have sorted but I can't fix or figure out this one. When the truck is cold it runs fine. The longer it runs the worse the misfire gets. The hotter the outside temp the worse it gets.

Going to work in the morning the truck is fine. Coming home the same distance it acts up. Idleing at lights seems to make it worse in the afternoon but smooths out a little once you get moving.


The timing is at 10 degree, fuel pressure is good cold and when it starts playing games. New plugs,cap,rotor,wires. There are no cats. The TFI,map sensor,IAC,ECT, 02 sensor and coil are all new. The TPS reads .9 and 4.9v. The IAC reads 1.8 ish and the ECT reads .6 ish when hot and it misfires. I dont think i have any vacuum leaks.

The wiring harness was hacked but I fixed everything that i saw and it really didnt fix/change anything. I checked the grounds and the problem has never gone away. There are no codes at all.

On a cold start it dies unless you give it some throttle. Once it runs for 15 seconds it will idle fine. On a warm day it does not do that. I have ran seafoam in the fuel tank and some in the intake. I used to have a bunch of spark knock ontop of the misfire. I fixed the spark knock so I do not believe that the current problem is spark related. The fuel pump is supposedly new but i have 33 psi at idle and 37 ish when you give it throttle so regardless it works.


It has valvetrain noise but it is intermittent. Starting it in the morning it will go away but once it warms up it comes back. The rocker arm shaft seems to be unclogged and the oil is fresh/clean. It previously was dirty before I bought the truck.


Any ideas?

 

[hkerekes]

It did something else this morning. Before it warmed up when I shifted it would stumble and then take off normally. It seemed like it was loading up with fuel. My only guesses are the objectors or the regulator. It does not leak out of the vacuum hose.

 

[jhammel85]

Hmm...I would check out the Air Charge Sensor. Other than that, Check the wiring to the Oxy sensor. Those are the areas I would check 1st...

Have you gotten codes?

 

[hkerekes]

Act and oxygen sensor are new, I checked the wiring. The act has the correct voltage coming out of the sensor. I have zero codes

 

[hkerekes]

I put a new fuel filter on it even tho the old one wasnt that old. The previous owner said he replaced it and it looked newish.

I double checked the fuel regulator to make sure it wasnt leaking. The idle smoothed out and it was actually easier to rev and more responsive with the vacuum line unpluged. That doesnt make any sense to me what so ever. A vacuum leak should make it worse, unless the regulator is bad? No vacuum should be an increase of fuel pressure correct?

 

[greggloaj]

Misfire Only When Hot

I have same problem with a misfire on my 1997 Dodge Grand Caravan, 3.0. It only happens after driving it for about 1/2 hour, turning it off for about 30 minutes, and then restarting it. At this point it spitters and sputters and is un-drivable and trips a misfire on cylinder #1. I inadvertently left a vacuum line disconnected and the misfire disappeared. I already changed plugs, wires, and fuel injector--and also cleaned throttle body and put new gaskets on intake manifold. And now I'm stumped what it might be--EGR valve, oxygen sensors, distributor, or something else???