First of all I know this is on a Bronco but this is engine related and I thought my chances of finding the answer were better here so please don't delete.

I need some expert help on this one. I have posted this issue on some other forums and gotten some good troubleshooting tips but haven't fixed my problem yet.

I have a 94 full size bronco with a 302 and e40d. Originally it was sputtering and bucking and I tried a tune up and some other stuff and found two dead cylinders so I pulled the motor and put the 302 shortblock from my 87 mustang in there. I still have the sputtering problem though. When I first start it, all is good then after about a minute the idle drops and runs really rough and sometimes dies. If I give it a little gas the RPM's increase but still runs rough. If I floor it or at least 3/4 throttle it runs perfect. I have tried a TPS, fuel filter, plugs, wires, cap, rotor, air filter, and I went to fordfuelinjection.com and tried to troubleshoot it from there but I could not get the codes from it. I tried jumpering the STI to ground and counting the blinks from the check engine light but it would not blink. When the engine is on there is no check engine light. I personally know that the engine is good mechnically as I built it, not that I am god or anything but this really seems to be an electronic problem and I am stuck on it. I tried to scan it with a really high quality Snap-on scanner that I know works and it said that it couldn't communicate with the computer. Any help on this would be greatly appreciated. At this point that old carb looks good but I would still like to fix it with fuel injection instead of going carb if I can.

 

How did you find the two dead cylinders originally? If you still have the problem with an entirely different engine, check those cylinders again and see if they're still dead. With the low idle, maybe the IAC is bad. Pull the plug off of it, and see if the engine will die. If it does nothing, the IAC is bad.

 

I had the injector harness fail coating was failing off under loom and connection were corroded. Just thought I'd through that in.

LOST

 

First i would look into the computer not communicating with the scanner. i have heard of corrosion in the computer plug.

 

Could even be the ECM itself......

 

I do need to pull the computer out and look at it, been dreading that because it doesn't look too fun to pull. Also, it will do this while driving also not just at idle and to make things harder to diagnose it doesn't do it a certain RPM just kinda at random. If I give it atleast 3/4 throttle it runs like a top and when you let off it will sometimes go right back to running like crap and sometimes not for a few minutes - all of that while driving. The two dead cylinders were at 0 compression on the motor that I pulled. I have checked the fuel pressure also and I can't remember exactly what it was but it was good. It's been a while since I checked it but I remember that it was good. I would like to thank you guys for some more insight, hopefully I can get her going good soon. I have to trade my tacoma double cab in, new baby will be here anyday and two kiddos just won't fit real well in it. I think I got the wife set on a v8 explorer though.

 

just pull the inner plastic fender half out and its not to bad 15 minute job if you dont start breaking or stripping screws.

 

There's just 1 bolt holding the wiring harness on the computer.. it's drivers side firewall down low. You can then remove the kick panel inside the cab and unbolt the ECU.. another couple small bolts. I suspect you may have some corroded pins on that connector.

 

Well I don't know how to thanks you guys enough, I found a couple lightly corroded pins on the harness at the firewall. I cleaned them with some alcohol and it's running just fine now, smooth idle and all. I will have to wait until tomorrow to get some electrical contact cleaner and preservative to treat it with but just the alcohol seems to have atleast identified the problem. I know all about how to treat corrosion on electronics....I have 9 years and counting as an Aviation Electronics Technician in the Navy.

Once again many thanks.

 

well.....maybe it's not fixed. It started running rough again last night. I haven't been putting miles on it just running it in the driveway. Today I took it out on the road for a quick trip around the block and it started the same symptoms all over again. I pulled the plugs and it is running rich. 1&5 weren't too bad but it's progressively richer towards #8 which had a good bit of carbon. This is my theory, tell me if I am out in left field or does this sound logical, I think that the fuel pressure regulator may need replacing. I don't have a gage handy to check the actual pressure but the plugs don't lie. At idle it starts fine and then drops to about 450rpm and then gets back up to about 900-1000rpm. While driving or in the driveway when it drops the rpm's and I press the accelerator pedal it will clear up and sound great, not a miss or anything...runs perfect but when you let off again it will go back to running rough. It sounds to me like when you rev it up its getting enough air to give a better air/fuel ratio and obviously runs right but at low rpm's it is just rich and will bog down.

I am thinking changing the FPR will make a difference but does that make sense?

 

id say 02 sensor my truck ran kinda similar and when i changed it ran much better

 

Well after more troubleshooting I replaced the computer and it seems to run right now. I took it around the block and it seemed to run just fine. I am not going to call it good until I put a few more miles on it though. I am keeping my fingers crossed that it is good now though.

 

Well, after a few weeks and more neighborhood miles, I think that I have it fixed. My guess is that the corrosion on the EEC connector spread into the computer. I cleaned the pins but didn't open the computer to inspect it. Thanks again for all of the help that was given.