My 91 F150 (straight 6, manual) has been having an intermittent problem. While idling or driving it will begin studdering and sometimes stall completely, sometimes I get a check engine light. Always restarts afterwards. While driving I get the studder and sometimes even a misfire.

Cleared codes.
Pulled the codes two seperate after problem happened, and got the following #'s 112, 117, 122, 126, 327
These are low voltage codes for ACT, ECT, TPS, EVP, MAP/BP.

So it looks like I am getting codes for all of my 5 volt transmitters, Checked TPS, ECT, and MAP supply voltage with meter while truck was acting up and it is bouncing around. Good steady supply when not studdering. 12 volt system and power to EEC stable during problems conditions. No grounding problems I can find. Problem does seem to occur more often when it is rainy.

Today It was rainy and studdering was occuring really often So I began disconnecting sensors one at a time TPS, EVP, and ECT no effect. Engine stalled out even when disconnected. When i disconnected MAP, no studdering. Reconnected and it stalled out. Did it again and same thing occured.

I was leaning toward a bad EEC since it supplies the 5V referance voltage, but now it looks like a bad MAP sensor.

My question is why would a bad MAP pull down the 5Volt supply to the other sensors? Can a bad MAP be grounding out in the sensor somehow or do you guys think I have a different problem?

 

I can't explain it, but like I said before I had virtually the same symptoms on an E 150 van and the MAP fixed it. When it is running right try tapping the MAP sensor. It probabaly stumble and stutter indicating a bad sensor.

 

I know jjstanza, you'll probably be able "I told you so" once i get this fixed. Since last week I hadn't had time to mess with my truck any until this morning. This morning is the first time that it would studder often enough for me to read different voltages and disconnect different sensors (Usually it'll do it once every 15 minutes). I just wanted to hopefully get some more input before I spend the $.

 

how old are ignition wires?

 

I've had my truck for a little over 3 years. I would guess the ignition wires are original. Why do you ask? Could they affect the 5Volt ref power?

Funny that you should ask about the ignition wires because I didn't mention it but I have another problem where I turn the key and nothing happens at all. It acts like I don't have the clutch pushed in or some other interlock. I try 2 or 3 more times and then it starts just like normal.

 

wet weather and old ignition wires do not play well together.

if the wires are original it is time to replace them.

check the spade connector for corrosion at the starter.

do you have motorcraft copper plugs in now?

 

striker_wvu if you are near Columbus Ohio I will give you a MAP Sensor. And I would hope you didn't get the wrong idea when I said " can't explain it, but like I said before I had virtually..." I wasn't trying to say I told you so, just wanted to remind you of the previous longer post.

Have a great day!

 

I'm back after a couple days. Replaced the MAP sensor with an extra my friend had last Monday. Drove the truck to work Tuesday-Friday and no problems (all nice sunny days). Started it this morning and it was shuddering and stalling as soon as it started. Voltage on the 12 volt system was fine but the voltage on the 5 Volt for the sensors was bouncing up and down. Was very rainy this morning, so that seems to definately be a factor. Last two times problem has occured are the last 2 times I have tried to drive it in the rain.
Not sure how the inginition wires would cause flucations in the 5 Volt reference signal? But I'm willing to look at what ever?

Never really had a grounding problem, would it act like this?

 

wires are cheap id try them first, if u dont know how old the wires are then they probably need replaced. start up ur truck at nite and pop the hood,ill bet it looks like a lightning storm under there

 

Hopefully it keeps raining tonight so i can look for some action under the hood.

 

Thought I'd follow up on the solution to my problem.
About 2 weeks ago I finally pulled my old computer out (didn't do it sooner since it is not usually a problem) and took the cover off. I didn't really expect to see anything wrong and at first it looked fine. Looking closer I saw a small dark, slightly bubbly area at the bottom of one capacitor leg. Then when I wiggled that capacitor I could see that one leg was not connected. Ordered a new computer from Advance Auto (took a week to come in), put it in a week ago and has been driving great since.

 

glad you found the elusive problem.