I have a 95 Full Size Bronco that just started out bogging and stumbling last Saturday. I replaced both the pickup coil inside the distributor and the ICM on the fender well. No luck what so ever. I relented then and bought the small laptop style code reader from Actron with the appropriate ford module. The device is fairly amazing. Anyway it says that I have an:

"IDM input to PCM SPOUT signal loss, circuit grounded" condition.

I spent a really long time in 115 Degree temperatures in a NAPA parking lot yesterday while we all took turns trying to find the PCM in the vehicle. It turns out that the little bugger looks just like a large connector going through the firewall. The PCM is mounted vertically and on my year anyway (1995) it is the connector closest to the fender on the drivers side. I had to get to it to acquire the Ford vendor code as there are about 3 different model controllers for my year according to our local Ford dealer who NAPA had on the line.

I plan on pulling the connectors off of the ICM and the PCM and then testing the wire against ground. If this does not disclose a short to ground then I will replace the PCM. I hate to do it needlessly because it is a big ticket item. I have ordered all the Factory manuals but they will not be here until next week. I hope we can keep the old Bronco running till then.

I am posting this in 2 places hoping to get the Old Ford Guys attention and opinion on how to proceed.

I also purchased a fuel pressure tester that I will check rail pressure with to see if that gives me any clues.

Just in case this may help anyone reading this in the future. I have already replaced the ICM, the Distributor pickup coil, and the fuel filter.

I will ride this out with you guys until we find the problem, then let everyone know what it was, as this “Stumblin’ Bumblin’ Bronco Thing” seems to be a common problem.

 

im in the same boat with my 94. hope the answer pops up soon

 

Yeah it seems a very common problem. My code reader shows a 121. So I think it is telling me there is a TPS problem. This Stumblin', Bumblin' Bronco thing is so dang intermittent I just cant tell if this problem is actually there at the time of testing. I have finally given up and bought a new sensor, I just got home. As soon as the Duststorm blowing outside calms down I will try it and let you know.

 

I have posted on occasion the concern where battery acid causes B+ to migrate into the hego sensor wire because the hego harness runs along the battery to starter cable. Very hard to catch unless you have monitored the hego and sudenly see 1 - 3 volts instead of .1 - .9. I have diagnosed this many times in my Dealership. When it happens the vehicle can do many weird things. (Buck, hesitate, stall, black smoke, etc.) Norm.

 

Thank you Norm. I was hopping you would drop by. I will check that in the early A.M. I finally think I have found my particular broblem. I hooked up a Fuel Pressure Guage to the injector rail. Everythin looked to be in spec. But with the intermittance it is always so hard to tell. Anyway I hit on a plan. I ran the pressure guage out the back of my hood, and then closed the hood to the first latch instead of all the way. It was 1:45 am and dark as can be out there. I was forced to use a bit of small rope to tie of the guage to point the way I needed it. Then I headed for my favorite test hill. While driving along with a pen light shining through the winshield I observed my rail pressure under actual conditions. Sure enough when the Bronco started to buck, the pressure dropped to about 22psi. I hade always been able to solve my problem for the short term by stopping the engine and then restarting again. So I did so and sure enough full pressure returned.

I bought a new fuel pump. I knew it could be a regulator or some other problem, but hey I think 110,000 miles is a good time to replace a pump anyway. So early this morning (4:am) we got up and dropped the tank. Of course first I had to drain it. I could not really get enough hose to siphon it the way the Haynes manual suggest, so I tried something else. And this accidentally led me to what I think is an exciting new test for this problem. Here is what happened. I had often suspected that maybe the pick-up screen was restricted, especially after replacing the inline with no good results. Well I had to get out 16 gallons of fuel so I located the Fuel Pump Relay and jumped it after placing the hose at the frame mounted filter in a gas can. The pump started up sounding strong as it should, but within a less than a minute it started making a slurping sound. A lot like when you get to the bottom of a drink with a straw. I repeated this test many times. Well of course when I got inside of the tank i found the pump fine but the strainer restricted. At my mileage I replaced the pump anyway. It was very hard changing that tank all alone. The truck runs SUPER now. I am thinking that many things might creat the symptoms I experianced. But next time, one of the test I will perform will be the KJ7YM (my ham radio call sign) slurppie test. Much easier than pulling the dang tank to look at the strainer.

I really hope I have helped someone out there the way the OLD Ford Guy has helped me so many times in the past. Thank again Norm. We all apreciate you.