I have posted this a few times before, but thought I'd give it one more try.
My '86 F250 has been in the shop for 4 months now. The problem is a bad shudder. Really bad.
The guy I bought the rig from put over $10,000 into it before I got it. The entire driveline is new or rebuilt. Jasper built AOD, all new Auburn gears, both axles and transfer case rebuilt.
When the shuddering started, I thought it was the transmission. We replaced the new trannie with another new trannie, built a new driveshaft, etc. etc.
A certified Ford mechanic has been after it for two months. At this point it is in the engine/ EFI.
We have pulled the intakes off, checked the injectors, etc. The diagnostic computer at Ford says that under certain conditions, injectors (3&4?) are dropping out as if the PCM was getting a signal from the O2 sensor that the thing is running too rich.
We swapped in a distributor from a known good running engine. Vacuum is slightly low at 17 inches, but very steady. Vacuum lines were tested using a smoke generator looking for leaks, but none was found. The line to the O2 sensor is showing between 3 and 5 volts, when (I am told) it should be less than 1 volt. The guy checked all the grounds. Once the voltage issue was found, Ford thought surely it was the PCM. We got a new one and it made no difference.
I have never had a case where the mechanics were saying that it couldn't be fixed, but they are running out of ideas.
So the suggestion is to bag it and tear off the EFI and go back to a carb setup. I guess I can, but I really would rather not.
So I have two questions.
A. What's wrong with my truck?
B. What are your thoughts on converting back to a carb?
Input will be greatly appreciated.

 

I can relate with you. I have an 85 BII and I had problem with the computer not advancing the timming so thing couldn't get out of its own way. I spent 1 month working on it and getting every reading to test out right. I took it to and auto elec. specialist and he could not find it, he suggested the repair wold be to rewire to truck at the cost of $1500. So I swaped back to a carb for about $300 and it has run good since.

400m

 

Hey Bob,
While I don't have an answer to your problem, I can relate with 400m's post. I have an '83 F-150 4x4 with a 302. When I got it it had the non-adjustable crank trigger ignition, feed-back carb, dura-spark III igniton with PCM, and wouldn't pull a greasy string out of a cat's behind. In short, it was just a lousy set-up. I replaced the camshsft, got a points dist. out of a '73 mustang and added a pertronix ignitor, then got a autolite 2100 carb off a '73 mustang, took my time and adjusted everything, and now my truck is a daily driver. It runs 100% better than before. Cranks excellent hot or cold and while the mileage isn't all I'd hoped, I know the engine is shot internally so it's not these mods fault. I know you didn't want to hear about switching to carb but if you're at the end of the line as far as tech goes, that may be your answer. However, there is still the legality of all that to be dealt with. If you have emissions testing in your area even that may not be an option. I understand your dilemma, I hope you get it worked out. Keep us posted.

Chuck

 

I have some Ideas but I need some more info


when does it happen? under load? while driving or parked?

Would you descibe the shudder as : the engine cutting out? or a shake that effects the whole vehicle?

when it shudders do you feel a loss of power?

does it happen when your accelerating, deccelerating, or both?

 

What engine do you have?

 

[updated:LAST EDITED ON 21-Jun-02 AT 09:43 AM (EST)]My engine is 5.0, EFI. We have been through it pretty thoroughly and it appears to be in great shape mechanically.
The shudder happens between 40 and 50. Everything (well obviously not everything or I wouldn't still be writing) has been gone through and checks out. The entire drive line is new.
It doesn't have to be under load. I can feel a slight "pulsing" almost like a harmonic shake, on a smooth flat road, but it is most definite when pulling a slight grade in this speed range. It is the whole car. You don't feel it in the steering wheel like a front end problem would be. And you don't get it in the gas pedal like a u-joint or driveshaft problem.
The Ford Tech who has been working on it most recently seems pretty convinced it is in the EFI. He can see fuel injectors dropping out under some conditions. Right now though it seems to be running great. For a small engine in a big truck, it feels real healthy when you put your foot into it.
I am seriously considering making the swap to a Ford Motorsports Mass Air System with all new sensors, harnesses and ECM. I just hate to spend the Money and then have this damn shaking.
As for your specific questions:
It doesn't seem to be on acceleration, more when making a steady climb. There doesn't seem to be any loss of power, though I could believe it was an engine issue.
Thanks for the interest.
Bob

 

Hello Bob...man, those hard to find troubles can sure drive a guy crazy! At first I was going to ask if it was a 4x4, thinking that the pivot bushing in between the ifs front suspension could be worn out. But then you said it was occuring under load...not necessarily under acceleration though...and that the ecm was showing a rich condition. Have you tried the coolant temp sensor? They are usually easy to check (resistance with an ohm meter). I'm sorry I don't have ford specific specs, but a coolant temp sensor may be telling the computer the coolant is cold making it think the engine needs the extra start up fuel for a cold engine...sort of like the choke staying on. I also believe the fuel pressure regulator is vacuum operated & may cause trouble not only with delivery, or too much delivery...but also in a vacuum leak sense. Just another guess, but maybe a vacuum leak causes a lean condition & the computer overcompensates by pouring more fuel to it.
Sorry if I have just caused more confusion, and although I used to be a heavy duty mechanic, I am in no way saying I know anything about ford fuel injection. I just tried to think what I would check. You will find the problem...don't just keep throwing expensive parts at it until it goes away. There must be someone who has had similar trouble, all you have to do is find him haha! Good luck, & I really hope that the whole problem is mud in the wheels, or something easy like that!
Randy

 

Surprisingly the Ford Tech has been great about not throwing in parts.
As for mud in wheels etc. I got a complete stock set of wheels etc. had them balanced and ran them for four months just to eliminat that issue.
In checking all the sensors of the EFI, the only odd reading we are geting is almost 5 volts on the O2 sensor wire, which should evidently be less than 1 volt. Put in a new O2 sensor no change. This made us think maybe the ECM, so we got a new from Ford unit which made no difference.
Also getting a slightly low 17" of vacuum, but it is rock steady. They tell me these early speed density systems are much more sensitive to changes in their world. I may spend some time and swap out vacuum hoses.

 

If I were you, I'd strip all the "looms" and insulation back and expose all the wires from the computer to the engine (sensors), My truck had bare connections from the factory that had corroded and rotted. I didn't find this out till I gave up, bought a crate engine, and pulled the motor.

Anyway, that's my guess.

 

Well from what you describe, I'd say the problem is almost certainly not electrical or ignition related.

I'm not sure how ford's scantool data works (I'm actually a GM Mechanic) but I'd be interested if your tech is actually seeing the fuel injectors stop firing, or if he's actually just watching those cylinders miss.

If he is getting a missfire at a certain RPM I'd definitly hook up a fuel pressure guage where you can watch it while your driving to see if when your truck starts pulsing if your fuel pressure is dropping off, and causing your engine to miss.

I'd also check the vaccum lines from the transmission modulator valve, and the brake booster, too see if your succking tranny or brake fluids into your engine, causing it to miss.

My other thought on your problem is a balance issue.

When you changed transmissions, did you also replace the torque converter? I've seen a few of those get out of balance.

if its the original converter, unbolt it from the flywheel, spin the converter 180 degrees while holding the flywheel still, bolt it back togethetr and go drive it, if the vibration chages youve found your problem.

if the converter has been changed, do the above procedure anyway, it'll tell you if your flywheel is balanced correctly.

my last Idea for now is to go to a body shop and have your frame measured, a bent or diamonded frame could cause a vibration.

 

I had a problem with my 87 Bronco shuddering under a light load.
It turned out that one of the sparkplug wires was cutting out.
Good luck!

 

Since you stated that your mechanics are professionals they surely road tested your vehicle at your shudder speed in different gears. This simple test will tell you if the problem is engine or drive. If the shudder occurs at 50 regardless of what gear its in and if its a 4x4 that has a tendency to suddenly jog to one side or another the problem is probablly the front drive u-joints, or perhaps the rear axle bearings or hard surfacing is worn (high milage or rough use). If the shudder is fixed to engine RPM hopefully they swapped injectors around to eliminate them as the problem.

 

I had posted earlier about my bronco and you stated that no matter what you did you were still getting 5 volts from the O2 sensor. That means you have an open circuit and it is in essence backing voltage into your O2 to pcm circuit. This may deffinitly cause the pcm to interupt the proper firing sequence of your injectors(dropping out). This was the problem with my Bronco II. My problem was the I could not determine were the crossing circuits were. What your looking for is similar to an open draw that sends your battery dead misteriously, and the 5 volt reading your 02 sensor is giving is similar to when you pull the ground off the battery and mesaure a voltage when there shouldn't be any. I hope this helps cause man I know the feeling!

400m