Fuel system issues.....i think....help please!
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Mountain Pass
Joined: Dec 2005
Posts: 133
Likes: 1
From: Mackinaw City, MI
Fuel system issues.....i think....help please!
Ok here goes: I have a '93 F-150, 4x4, AOD, 5.0, which is fresh(new pistons and rings, bearings, underdrive pulleys, Comp cams valvetrain, stock intake, aftermarket 19# injectors, shorty headers, cat delete, Flowmasters, ignition components are fresh, MSD coil, K&N FIPK, etc, etc,etc,). It ran GREAT for two weeks then all of a sudden it wont run. It starts and will run for 5-10 seconds then dies. No check engine light at all. Plugs are wet fouled after 3-4 start ups. Fuel psi with key on is 25-28psi(which I know is below spec), engine will start then dies, but upon dying fuel psi goes up to 35psi. While cranking, fuel psi is erratic, but will continually foul the plugs after a few starts. Fuel psi regulator is new also, and does hold with a vaccum pump on it. This truck has dual tanks, and shortly before the issues, rear tank was pumping into front tank, this truck doesn't have a selector valve on frame, just a switch on the dash. Losing my patience here, anyone else run into this before? 
Any suggestion on how to remedy this would be great, thanks.
Any suggestion on how to remedy this would be great, thanks.
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
The front tank has a bad shuttle valve in the Fuel Delivery Module. It may be bad enough most of the pressure from the rear tank may be siphoned of to the front. That would account for the low fuel pressure.
In light of the gas fouled plugs I would also suspect you have a weak spark too.
In light of the gas fouled plugs I would also suspect you have a weak spark too.
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Mountain Pass
Joined: Dec 2005
Posts: 133
Likes: 1
From: Mackinaw City, MI
Ok, I replaced the front tank fuel delivery module. Fuel psi is now a steady 35psi and it holds, but after 3-4 attempts to start it just fouls all 8 plugs. This is the 3rd set it has done this to. The pressure regulator on the rail has already been replaced. This engine has an MSD Blaster coil, which I believe delivers great spark. I swapped it out to my 88 Ranger 2.3 and it runs fine on it. Wires were new a month ago, cap and rotor also. What else can be the source of weak spark? Ignition module or distributor stator? I thought those were 'go or no go' parts, or can they grow weak? This engine will start, but then immediately dies, black smoke coming out the tailpipes. Chasing a gremlin here i think, any ideas anyone?
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
MAP sensor comes to mind for causing a rich condition same for the Engine Coollant Temperature (ECT) or Air Charge Temperature (ACT) sensors. I do not recall reading if you checked for codes. Even with no Check Engine Light you can have a bad sensor or stored code in Continuous Memory (CM).
On the other hand any of those sensors can be bad but still within normal range. Once we confirm if you checked for codes by running the Key On Engine Off (KOEO) tests and CM check it may be time to break out the meter to verify those rascals.
For reference: Fuel Injection Technical Library
On the other hand any of those sensors can be bad but still within normal range. Once we confirm if you checked for codes by running the Key On Engine Off (KOEO) tests and CM check it may be time to break out the meter to verify those rascals.
For reference: Fuel Injection Technical Library
Thread Starter
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Mountain Pass
Joined: Dec 2005
Posts: 133
Likes: 1
From: Mackinaw City, MI
Ok, I switched the MAP sensor with a known good one, and it ran decent. It did have a check engine light, so I pulled the codes. They were codes for KOEO/KOER TAB & TAD solenoids, which I have had disconnected. There was a CM code for EGR valve not opening also.
The next day I bought a new MAP sensor, drove the truck home and it died in my driveway. It loaded up and died, plugs all fouled out again. WTH? It's possible I can borrow the used sensor that it ran decent with, but there has to be something else going on here. All 8 plugs are soaked when this happens, this will be the 5th set. Autolite loves me for this, any other ideas? PCM perhaps? Is there a way to test a MAP sensor? Really frustrated.....
The next day I bought a new MAP sensor, drove the truck home and it died in my driveway. It loaded up and died, plugs all fouled out again. WTH? It's possible I can borrow the used sensor that it ran decent with, but there has to be something else going on here. All 8 plugs are soaked when this happens, this will be the 5th set. Autolite loves me for this, any other ideas? PCM perhaps? Is there a way to test a MAP sensor? Really frustrated.....
Thread Starter
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Mountain Pass
Joined: Dec 2005
Posts: 133
Likes: 1
From: Mackinaw City, MI
If iy helps, all 8 plugs are soaked when pulled, the 4 on the right bank are completely black, fuel hanging off the electrodes. The 4 on the left bank aren't black, ceramics are still whiteish but fuel is hanging off electrodes as well.....after it is flooded I can pull the fuel pump relay and it will try to start 4-5 times on the accumulated fuel.
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
The link I posted earlier has all kinds of info on each sensor used on these vehicles. It also has what the values should be at difference operating temperatures. Yes, you can test a MAP sensor as well as the ACT, ECT, TPS and others.
Even though you stated the truck ran well for a few weeks you can also be compounding the problem by not having the TAB/TAD solenoids connected electrically if indeed they are disconnected. You can leave the vacuum lines off, and fail the KOER tests, but they should be connected electrically to prevent the PCM from defaulting to baseline settings.
With as much fuel you are dumping in I would have suspected a FPR problem but you already replaced it. That is why I suggested you check the other sensors with a meter.
Even though you stated the truck ran well for a few weeks you can also be compounding the problem by not having the TAB/TAD solenoids connected electrically if indeed they are disconnected. You can leave the vacuum lines off, and fail the KOER tests, but they should be connected electrically to prevent the PCM from defaulting to baseline settings.
With as much fuel you are dumping in I would have suspected a FPR problem but you already replaced it. That is why I suggested you check the other sensors with a meter.
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Mountain Pass
Joined: Dec 2005
Posts: 133
Likes: 1
From: Mackinaw City, MI
The link is helpful, gives a lot of parameters, but didn't answer all the questions i had. I tested all the sensors, on the engine, in question. All were within spec except TPS which tested at .84 Volts at closed throttle, the spec on the link suggested .9, with a 3% margin which applied to .9 volts would then be .87 Volts. I pulled codes, got KOEO codes of 21 (ECT out of self test range of .3 to 3.7 volts), 24(ACT out of self test range of .3 to 3.7 volts), 52 (P/S pressure switch always on or off), 81(Air Management circuit failure TAD), 84 (Canister purge solenoid circuit failure).
So again i checked ECT, ACT for voltage with key on and both sensors metered at 3.5 volts, within spec. Ran the self test again with the same results. I want to believe my meter at this point, it has been more consistent. Do you think the TPS being maybe .03 volts below spec is the culprit of all of this.......?
So again i checked ECT, ACT for voltage with key on and both sensors metered at 3.5 volts, within spec. Ran the self test again with the same results. I want to believe my meter at this point, it has been more consistent. Do you think the TPS being maybe .03 volts below spec is the culprit of all of this.......?
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Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
The link is helpful, gives a lot of parameters, but didn't answer all the questions i had. I tested all the sensors, on the engine, in question. All were within spec except TPS which tested at .84 Volts at closed throttle, the spec on the link suggested .9, with a 3% margin which applied to .9 volts would then be .87 Volts. I pulled codes, got KOEO codes of 21 (ECT out of self test range of .3 to 3.7 volts), 24(ACT out of self test range of .3 to 3.7 volts), 52 (P/S pressure switch always on or off), 81(Air Management circuit failure TAD), 84 (Canister purge solenoid circuit failure).
So again i checked ECT, ACT for voltage with key on and both sensors metered at 3.5 volts, within spec. Ran the self test again with the same results. I want to believe my meter at this point, it has been more consistent. Do you think the TPS being maybe .03 volts below spec is the culprit of all of this.......?
So again i checked ECT, ACT for voltage with key on and both sensors metered at 3.5 volts, within spec. Ran the self test again with the same results. I want to believe my meter at this point, it has been more consistent. Do you think the TPS being maybe .03 volts below spec is the culprit of all of this.......?
The typical TPS range is between 0.6 to 1.0 VDC at closed throttle. Your value of 0.87 VDC is within range. Use your meter to verify if the output is linear throughout the sweep to open throttle.
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Mountain Pass
Joined: Dec 2005
Posts: 133
Likes: 1
From: Mackinaw City, MI
After racking my brain night after night, and gathering loads of advice and info, I still had the same issue and no closer to a solution. On a hunch I decided to pull the PCM to inspect, and before I even pulled it I knew it was the culprit. It had been getting wet from water that had been leaking on it due to a bad windshield seal, then running down the A pilllar on top of PCM. This thing was so rusted and corroded, inside and out, I can't believe this truck ran at all. I replaced the PCM, resealed the winshield, and now the truck runs great! Thanks for the help 
FTE Legend
Joined: Jun 2006
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From: Ottawa, Ontario
Is the fuel tank evap system still intact? If so have a look at the charcoal canister to see if it's flooded with raw gas.. sometimes when there is a fuel transfer problem the other tank gets over filled and then so does the evap system, and then you get a whole bunch of extra fuel pulled into the motor.
If that's not your problem then you either have a wiring short in the injector harness or the computer has lost it's mind.
If that's not your problem then you either have a wiring short in the injector harness or the computer has lost it's mind.
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