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Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 35493
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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My name is ***** *****. I have a 1995 f150 5.8 XLT

Customer Question

Customer: My name is ***** *****. I have a 1995 f150 5.8 XLT w/California emission. Engine starts fine runs ok until hot. Then it stalls, stops and generally runs rough. Each time it stalls, it starts right back up. The MAF and ICM have been replaced. If I disconnect to MAF, it runs fine but shifts hard due to the MAF missing.
JA: Thanks. Can you give me any more details about your issue?
Customer: I had some pack rat damage, i.e. wiring to injector #3 eaten away. I replaced the connector and checked all other wiring and vacuum lines. All ok.
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Submitted: 1 year ago.
Category: Ford
Expert:  Ron replied 1 year ago.

Hello, my name is ***** ***** I am a professional here at Just Answer. I have noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

Can you start with installing a fuel pressure gauge to the fuel rail service port and monitor the fuel pressure when it stalls. Normal pressure need to be right at 32 to 45 PSI. Check this for me and post back when you can and we can work from there. Im off today but will be here all day on Monday.

Customer: replied 1 year ago.
I hooked up a fuel pressure gauge to the fuel rail. It measured 40psi when the ignition switch is turned on and 34psi when the engine is running. After the engine warms up, (10-15 mins), it will abruptly stall, as if the ignition was turned off and the fuel pressure goes to 40psi. If you disconnect the MAF, the engine runs fine and does not stall. The only problem is that it shifts very hard, which I believe, is a product of the PCM not getting the MAF signals. The MAF tests ok, (i.e. voltage output varies between .1 and 2 volts) as the engine rpm increases. The ICM has been replaced.
There are two tanks in the truck. The engine stalls with either tank selected. The fuel filter has been replaced. I am still troubleshooting and still need help.
Expert:  Ron replied 1 year ago.

In most cases if the Engine runs fine with the MAF unplugged that usually means the MAF is bad. Are you sure its checking okay?

Customer: replied 1 year ago.
I put a multimeter across the signal output and ground (via two needles in the wires) to measure the DC component of the signal. The MAF was replaced by our local Ford dealer who installed a reman unit. I brought it back to the dealer when it did not fix the problem and they said the MAF was good and I needed to replace the ICM. I replaced the ICM to no avail. Obviously the dealer's techs don't know squat. I have suspected that the MAF was bad, but the only way to prove it is to put in a new one (not from the sleasy Ford dealer) but from an auto parts store. If you know for sure that the engine should not run with the MAF disconnected, I will buy a new one and install it.
Expert:  Ron replied 1 year ago.

When it stalls are you able to tell if you actual loosing spark?

Customer: replied 1 year ago.
I put my timing light on the coil output and also various plug wires and spark looks good, but obviously, when the engine stalls, the spark goes away. Remember, the engine starts right back up. I considered a thermal short in the coil, but since the engine runs with the MAF disconnected, the thermal idea pretty much falls short.
Expert:  Ron replied 1 year ago.

I would agree, in most cases if the coil fails it dose not come back. If unplugging the MAF allows it to stay running the you have to be Masking something. I have to wonder if the PCM is not at fault.

Customer: replied 1 year ago.
That was my worry as well. Murphy's law dictates that the problem will be the most expensive part (and hardest to get). Any way to isolate it to the PCM before replacing it?
Expert:  Ron replied 1 year ago.

Unfortunately there is no test for a failing PCM beside replacing it with a known good unit. The 1995 is a plug and play unit with no programming needed , Have you tried locating a used one?

Customer: replied 1 year ago.
My truck has California emissions on it and I was led to believe that the PCM is different from the others.
Expert:  Ron replied 1 year ago.

It is just a bit but any 1994 5.8 PCM would still work to at least answer the question as to if its bad. If it is then you would want to stay with the CA emission PCM.

Customer: replied 1 year ago.
I will try to find one and let you know.
Expert:  Ron replied 1 year ago.

Okay, post back when you need me. Im here everyday.