1990 Ford F-150 engine now completely dead - but normal hear

Tiny
TIMM1954
  • MEMBER
  • 1990 FORD F-150
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 17,600 MILES
I'm an experienced shade tree mechanic for over 33 years but this one has me stummped. My strait 6 engine which I bought runnig bad, would at times run 100% and very strong after a difficult time starting. I have filled both tanks to full, one was already full. It seemed to run better when it was warmed up. But then it was like ssomeone pushed a button and it would start running lousy with a intermitting miss. Then, it would happen again, start running 100% and strong. The next time I tried to start it it back fired and blew off the muffler. Yeoww!
Then, I couldn't start it no matter what I tried, even after spaying stater spray in the intake. Here is what I have done to try to find the problem. I checked the fuel line pressure, good. Checked both pumps independently - running and pressure good. Checked for codes - no codes (very frustrating) replaced the MAP sensor. Replaced the water temp sensor. Replaced the Fuel pressure regulator valve. Took the timing cover off and checked the timing gears and timing - O.K. Like new. Replaced the ICM module on the distributor. Then replaced the distributor pickup module and rotor inside the distributor. Replaced the rotor and cap, sparkplug wires & spark plugs. I get a strog spark. Did compression check about 145 on all cylinders. Replaced the coil. Checked the injectors for clogging all clear and spraying. Replaced the fuel filter. Checked the mechanical timing again all good. Replaced the idel speed control valve. Video taped with the valve cover off and spark pulg wire on a spark plug for number one, then slowed the video down on my computer to wath the timing while cranking. The timing and spark to valve action is perfect. Next I pulled the injector rack off, zipped the injectors tight to the rail and video taped the cranking sequence. At first I get 8 all injector shots every 1/2 second while cranking, but then it injects right when the exhast valve starts to inguage. Ah Hah - this is out of sequence right. Could this be my problem? What controls the injector pulse since there is no crank or cam position sensor on this model? See I've got everything that says this truck should run - but nothing! Help!
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Saturday, October 11th, 2008 AT 10:53 AM

11 Replies

Tiny
RACEFAN966
  • EXPERT
The injector pulse is controled by the computer itself.
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Saturday, October 11th, 2008 AT 11:47 AM
Tiny
TIMM1954
  • MEMBER
Yes, I know the computer controls the impuse, but how does it know the timing? Because it is off. The gasoline is going out the exhaust cycle it seems. At least I'm thinking that is what is happening. How can I put the injectors back in time? The computer is no longer available from the dealer. A friend replaced the computer from another running truch but it didn't make any difference.
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Saturday, October 11th, 2008 AT 12:24 PM
Tiny
TIMM1954
  • MEMBER
Yes, I know the computer controls the impuse, but how does it know the timing? Because it is off. The gasoline is going out the exhaust cycle it seems. At least I'm thinking that is what is happening. How can I put the injectors back in time? The computer is no longer available from the dealer. A friend replaced the computer from another running truch but it didn't make any difference.[/Quote:a11bef9fba]

I also checked the gasoline for water and flamability. It is good, no water and quite flammable. I did change the fuel filter. Is the injection signal controlled by the little pickup signal from within the disributor and sent through the ICM module to the computer? Maybe something is off time in there?
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Saturday, October 11th, 2008 AT 12:36 PM
Tiny
RACEFAN966
  • EXPERT
The timing is controled by the hollowfect distributor and the module which is sent directly to the computer to control the injector pulse. Then the knock sensor is used to retard the timing if there is pinging. Now if by chance the knock sensor is not reading correctly the timing would alway's be retarded. You should have 5 volts reference to it and when it is told to retard it sends a signal back to the computer and therefore retarding the timing. So with that unplug it and with key on engine off find the 5 volt reference wire and note the color then turn the key off and plug it back in and turn the key back on and check the signal wire for voltage. If there is voltage then the sensor is bad and your timing will alway be retarded. Hope this is more helpful for you. Let me know if I can be of more help
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Saturday, October 11th, 2008 AT 10:13 PM
Tiny
TIMM1954
  • MEMBER
Well, I tested the knock sensor. It's good and the voltage is good. Also put the timing 180 deg. Out still didn't start. Put it back in time again to valve action. I also replaced the Oxegen sensor. I mean just about everything on top of this engine is new and it still wont start. I've tested stuff to the dang book and traced out the wireing harness and can't find anyhing bad or bad grounds. Even though I get spark when cranking it acts like there is no ignition at all.
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Tuesday, October 14th, 2008 AT 11:30 AM
Tiny
RACEFAN966
  • EXPERT
You are getting fuel right? Just asking to make sure. If you have spark and fuel then it should start. You have checked the TPS right? If the computer thinks the throttle is open when infact it is closed it will not start or run either. Let me know and we will go from there.
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Tuesday, October 14th, 2008 AT 8:26 PM
Tiny
TIMM1954
  • MEMBER
Yes I have gas spraying from the injectors, took the rail off and cranked it to see for myself. Good strong sqirts. Also fuel pressure is 30 - 35 lbs. I do have spark also, replaced everything ignition. Except the resitor wire in the wiring harness. Rotated the engine by hand and set the timing to Top Dead Center and according to the valve timming, so I know for sure the seqence is in time for the intake and exhaust and when the spark needs to hit number one cylinder. Cranked it and can see a spark on a spark plug grounded to the engine. THIS THING SHOULD RUN! I also replaced the ignition switch just on a hunch. Didn't make any difference. I traced out the wiring harness today but didn't find anything amiss. I've just about given up. This thing has me stummped. I appreciate any ideals.
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Tuesday, October 14th, 2008 AT 10:20 PM
Tiny
TIMM1954
  • MEMBER
Oh yes throttle Position sensor good.
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Tuesday, October 14th, 2008 AT 10:21 PM
Tiny
RACEFAN966
  • EXPERT
I can't remember it I have asked or if you have already answered this but have you pulled codes to see if any where present? I am starting to think that the computer is faulty.
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Wednesday, October 15th, 2008 AT 9:51 AM
Tiny
TIMM1954
  • MEMBER
Yes I tried to pull codes and their were none. I think the spark and ignition signal somehow to the pip is all messed up sending a faulty reading to the computer for the injectors. I get a spark, but what difference would it make if the other signals were miss read or not even getting there. I've been trying to get this truck to work off and on for a month now. Spent over $500.00 or more on componets. I replaced the TFI module, maybe the new one is bad. That would explain a lot.
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Wednesday, October 15th, 2008 AT 11:30 AM
Tiny
RACEFAN966
  • EXPERT
Yes that would explain alot I would warranty it out and see if that fixes it.
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Monday, October 20th, 2008 AT 6:17 PM

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