Repair help!!

[jwilliams41]

I have a 94 b4000 with a strange issue. On a cold start up I can hear a miss, when I drive it still cold down the road it’s missing bad pretty much undrivable. Once I get roughly 2 miles down the road the truck stops missing like nothing was ever wrong with it. I have noticed it does it the worst when the engine is cold. The colder the engine the worse it is. I have replaced fuel pump, fuel filter and I recently did a tune up (plugs and wires) about 3 months ago. It’s an obd1 vehicle with no check engine light on. I have done a compression test with the results being lowest cylinder 120psi and highest being 133psi. Any ideas? Anything feedback will be appreciated! Thanks!!

 

[SMSgt09]

Have you ever put a code scanner on it? You should be able to do that for an OBD1. Just for a shot in the dark I would check the temp sensors and possibly the O2 sensors. You might need to do some searching to find what the different resistances should be on the sensors you test. Or just start with the cheapest first then work from there. You just might get lucky.
Good luck
Kent

 

[jwilliams41]

Thanks for the reply! I have an obd1 scanner and even though it didn’t throw the check engine light it was showing 2 codes. One for the intake air temp sensor and one for the DPFE sensor both being out of range. That was where I was going to start first replacing both of those. It said for the intake air temp sensor 58k ohms at 50 degrees. I removed the sensor and it was 56 degrees outside and I was getting a reading of 34k ohms which seemed a little off to me. So I’m going to replace those and see what happens. I have already tested the harness back to the pcm and everything tested fine. Again thanks for the feedback!!

 

[roscoe 0202]

before you replace the dpfe check fuel pressure if it is low the egr will be out of range no fuel no exhaust pressure
roscoe

 

[jwilliams41]

I checked it a few weeks ago and with KOEO I was getting 35psi. Thanks for your feedback!

 

[roscoe 0202]

check with engine running
roscoe
my book calls for 39 psi 35 should be adequate but that is with engine running

 

[410Fortune]

try changing that IAC and see what happens.......
35 psi is on the low side, does it hole 35 psi when you bump the throttle or does it drop?

Let us know what comes of this with those parts replaced.

 

[jwilliams41]

I just replaced the iat sensor. Took it down the road and seemed to be fine but it was a little warm here today and it usually doesn’t do it when warm. It seemed to idle rough for a few seconds then seemed like it straightened it self out before I drove it. Sprayed some starter fluid around intake, throttle body and vac lines and got nothing. I will test when it is cold first thing in the morning and see what happens. I just replaced the fuel pump a few weeks back but will test the pressures again tomorrow and see what happens. Again thanks for the help so far!

 

[410Fortune]

Nice! Lets see if that fixed it...time will tell

 

[jwilliams41]

Sorry I have been busy! I mainly work weekends because I also go to school full time. On top of working full time and going to school full time, my wife and I are expecting our firstborn in February!! So things have been pretty busy lately. Now with the truck the IAT didn’t fix it but it did seem like it cut a lot of the miss out. So today I drove it to school to work in the garage because it’s been raining here in NC. I got the truck to pass the key on engine off test and as many of you may know you have to pass that before you can do the key on engine running test. I have one of the cheap Ford obd1 readers, it makes it a little easier than counting flashes. So I got the 111 pass code for the key on engine off test. Next I tried the key on engine running test and got a 111 pass code again but it wasn’t missing when I done it. So I then let the truck cool off to try and get it to miss again then do the test. I got it to miss like it has been then I done the key on engine running test again and BAM!! Code 116 engine coolant temp sensor - sensor output voltage less than or greater than expected. I’m just letting you guys know I promise to post the fix just been a little busy.

 

[410Fortune]

Nice work! Engine coolant temp sensor.....you can either replace it or test it

 

[jwilliams41]

I’m going to test the harness and the sensor first. I’ll probably get to it later this week.