2.9l misfire or skip at specific rpm

[BIIman94]

I have been having an issue with a skip/misfire/stall around 2800 rpms but it doesn't do it every time and I believe there's a pattern with colder weather and when the engine is cold. I have checked for vacuum leaks, timing and run a scanner on it and came up with nothing. I am pretty mechanically inclined and have tried changing plug wires and such with no results. I kinda don't believe it to be a firing issue bc with my experience it would be doing it during full rpm range not just a specific area. Looking for anyone who's had this issue to give me some insight, also not sure if its related but if I barely give it throttle it will pick up normal then rpm will drop with me still holding throttle? Thanks in advance!

 

[RonD]

Couple of things come to mind.

The TPS(throttle position sensor) is like a volume control or light dimmer, knob type control.
It is a variable resistor, so a moving part that can wear out.
Computer sends the TPS 5 volts and then reads the returning voltage to set injector's open time(fuel delivery), under 1volt coming back means idle, above 4.5volts coming back means foot to the floor.
If there is a dead spot or resistance/voltage hops around, fuel delivery would be effected.
This sensor is easy to test with an OHM meter.
Remove connector hook up OHM meter and slowly open throttle while watching OHM meter, OHMs should slowly increase or decrease, which doesn't matter, what you are watching for is a sudden jumping up or down on the meter, meaning a bad spot.
Repeat opening and closing a few times, if all is smooth then TPS is OK.

MAF sensor and/or MAP sensor
MAF sensors do need to be cleaned, read here:
http://www.therangerstation.com/tech_library/CleanMAF.html

MAP sensors use a vacuum line to read intake manifold pressure, this is used to adjust fuel/air mix, the MAP sensor, if you have one, is usually located on the passenger side firewall, hidden by wiring harness, lol.
Find a vacuum line running at that location and the MAP sensor will be at the end, check the vacuum line for cracks, and check the connector for corrosion.
I don't think this would cause an RPM specific issue, but easy to have a look.


If you have a distributor and the TFI ignition system then it should be tested, read here:
http://www.therangerstation.com/tech_library/TFI_Diagnostic.html

Print off the worksheet

Distributor shaft should be checked as well, they can develop a wobble if bushings get worn out, this can cause misfires at specific RPMs that come and go.
remove cap and feel if shaft is loose, have someone turn over the engine while you watch for a wobble.

There is an IAT(intake air temp) sensor, but it is a gross reading sensor, used to lean out or richen fuel/air based on air temp, cold air is denser so needs more fuel mixed.
IMO, it would be hard for this sensor to cause an RPM specific issue.

 

[jhammel85]

I had the same problem and mine was the tfi

 

[BIIman94]

Thanks ronD I will be checking those things out, and jhammel I don't believe it to be the tfi module bc this is third b2 I have owned and both previous ones had tfi issues and they stemmed from it shorting out due to heat, this problem seems to happen more so when cold and I've never heard of the tfi shorting other than by heat. I could be wrong and if one of the things ronD pointed out doesn't pan out I will then look at the tfi

 

[a31ford]

Stupid as it sounds... Coil.

your problem random ? above 2800 the coil is so fast that the problem appears to quit, BUT in fact it's there, (I bet) just like mine was....

My coil looked fine, Until viewed in the dark, truck just slightly warm.

Here, see my post about it.

http://www.therangerstation.com/forums/showthread.php?t=147038

Greg

 

[BIIman94]

A31ford the problem is veryy random, it has done it a lot over the past couple days. It's always around the same rpm when it does it and gone after one hard miss/stall and it may do it as soon as I run it up again or it could be a couple days, I haven't been able to fool with it due to raining for like 2-3 days to try any of the possibles that Ron suggested


Update- I changed the coil, iat sensor and one other sensor today with no improvement :/

 

[a31ford]

Did you Find a fix ?? Bump ^