1990 F150 (no start)

[glhs875]

I have a 1990 F150 5.0 that has fuel pressure (new pump), spark but will not start (new computer). Will try to start with starting fluid. So it appears the injectors are not pulsing. any ideas?

[turbovanman²]

Any codes? What happened the first time? What's your fuel pressure?

[glhs875]

No codes. Only for sure known previous problem was bad fuel pump. Not my diagnosis though. Fuel pressure is around 45psi and holds while cranking.

[turbovanman²]

Hmmmmm, It could be a module, but then usually, you don't have spark. Fuel pressure spec is 35-45 so your good there. Will it stay running was you use ether or does it die right away?

Who changed the computer?

[glhs875]

I changed the computer due to research pointing at that. I am considering the module. But does that have anything to do with the injector pulse? Both leads at the injector (s) have voltage.

[turbovanman²]

Ok, that's an issue, only one lead should have power, the other is a ground. So you have a computer issue or wiring.

[thefitisgay]

well if the computer is bad causing no start the fuel pump will keep running with the key on... i mean it will not come out of self prime mode...

the problem with the computer is actually 3 capacitors that start to leak and eat the leads off of the capacitors

but that might be just the 6 cyls...

[glhs875]

The fuel pump cycles like it is supposed to do. I agree on both leads at the injectors being hot as a problem. Sounds like a ground has been lost?

[turbovanman²]

Ok, lets start from the beginning. What happened to start this diagnosis?

[glhs875]

Ok, lets start from the beginning. What happened to start this diagnosis?

What I was told is that the truck quit running. That was a few years ago. The previous people working on it (shade tree) felt like the pump was the reason for it to quit running. Of course after sitting for awhile the pump was certainly bad. The previous people installed a new pump/cleaned out the tank but no start. It has 45 psi on the fuel rail. Pump sounds good and cycles normally. Has spark from the coil to distributor cap, but no start! Injectors will not pulse. i installed new computer thinking/hoping that would solve the issue,no luck! The best I can tell,the relays are good. Both leads at injector has voltage. So the injectors are not being grounded and therefore won't pulse! WHY?

[RattFink]

It sounds more like one of the leads is shorted to power vs being grounded. There should only be power on one side of the injector. What are you using g to check for power dim or test light? Is the multi point injection?

[glhs875]

It sounds more like one of the leads is shorted to power vs being grounded. There should only be power on one side of the injector. What are you using g to check for power dim or test light? Is the multi point injection?

I used a test light. But I plan on breaking out the voltmeter today. If one lead is not grounded on the injector then both leads will have power showing even if only supplying power to one of side the injector leads.

[RattFink]

Yes if the injector is still plugged in while you are checking.

[glhs875]

Yes if the injector is still plugged in while you are checking.

It was.

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I'm gonna check the TPS voltage and see if that is okay. It has been brought up as a problem if it shows WOT will cranking.

[glhs875]

Checked TPS. 5v going in 1.1v showing on the output. So no problem there. I disconnected 1 injector lead. Still shows batt. voltage on both leads. Would the other injectors still being hooked up have an effect on that reading? Did i mention I hate working on Fords! LOL

[RattFink]

Does this truck have a crank sensor?

[glhs875]

Does this truck have a crank sensor?

No. Not that I'am aware of.

[RattFink]

Does the check engine light stay on while you are cranking the engine over?

[glhs875]

[QUOTE=RattFink;1061912]Does the check engine light stay on while you are cranking the engine over?[/QUOTE

It will go out when cranking.

[RattFink]

I think the injectors are bank fired so each bank shares a power and ground. Ford service info doesn't go back to 1990 so I was looking at a 1992 but should be the same. Ford interprets crank rpm from the distributor and it is called a PIP signal. It uses pip to fire injectors. During cranking the engine light shuts off as soon as pip is received by the pcm

[glhs875]

I think the injectors are bank fired so each bank shares a power and ground. Ford service info doesn't go back to 1990 so I was looking at a 1992 but should be the same. Ford interprets crank rpm from the distributor and it is called a PIP signal. It uses pip to fire injectors. During cranking the engine light shuts off as soon as pip is received by the pcm

I checked the top lead coming out of the dist. module which I think is the pip signal. It was showing around 1100 rpm when cranking the engine. This thing has me puzzled. So far everything i have checked seems to be okay!

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I think the injectors are bank fired so each bank shares a power and ground. Ford service info doesn't go back to 1990 so I was looking at a 1992 but should be the same. Ford interprets crank rpm from the distributor and it is called a PIP signal. It uses pip to fire injectors. During cranking the engine light shuts off as soon as pip is received by the pcm

BTW,I really appreciate you helping me with this!

[glhs875]

How are the injectors grounded to the block. And I understand the injectors are grounded by the computer in order to pulse so how can they be grounded to the engine block also and not stay open all the time?

[RattFink]

No problem, I work on a lot of Fords! Sounds like you've covered all the bases here. The ford pinpoint test isn't very long on a no start and you've checked most of it. They refer to using a breakout box alot though. Do you have access to a scan tool for this truck?

[glhs875]

No problem, I work on a lot of Fords! Sounds like you've covered all the bases here. The ford pinpoint test isn't very long on a no start and you've checked most of it. They refer to using a breakout box alot though. Do you have access to a scan tool for this truck?

All I have is a code reader. If I can find my adapter i have a snap-on scanner, would that help?

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I wish I had a known good computer to try!

[RattFink]

The other thing is pcm power and grounds, if the pcm isn't even coming on then the injectors wouldn't pulse. If you could scan it then it'd verify the pcm. Is powering up and maybe could view rpm pid.

[glhs875]

The other thing is pcm power and grounds, if the pcm isn't even coming on then the injectors wouldn't pulse. If you could scan it then it'd verify the pcm. Is powering up and maybe could view rpm pid.

Would a snap-on scanner be capable of doing this test. Or how could I run an aux. wire to manually power up the pcm? Say straight from the batt. but to what wire on the pcm harness?

[glhs875]

How could I manually check (which wires/color) at the pcm harness for a 12V source and also to make sure the pcm has a proper ground?

[turbovanman²]

Snap On scanner is useless for a 90, you won't see much or any data. The computer grounds the injectors which is how they are controlled, in MS. If you had a labscope, you could watch the pattern. I know its a pain but you could have a shorted injector which would give you the problem your having. One side you can get to, the other, the upper intake has to come off. i am at work tomorrow so I can give you the wires to check for power and grounds. Use the headlight trick to verify grounds. IIRC, if your getting spark, the dizzy and module are fine.

[glhs875]

Snap On scanner is useless for a 90, you won't see much or any data. The computer grounds the injectors which is how they are controlled, in MS. If you had a labscope, you could watch the pattern. I know its a pain but you could have a shorted injector which would give you the problem your having. One side you can get to, the other, the upper intake has to come off. i am at work tomorrow so I can give you the wires to check for power and grounds. Use the headlight trick to verify grounds. IIRC, if your getting spark, the dizzy and module are fine.

Any info on the wiring would be great to have. So you think a shorted injector could keep all of them from pulsing?

[turbovanman²]

Yep, wigs the computer out and you get the condition you have. You could ohm test the ones you can get to today.

[glhs875]

Yep, wigs the computer out and you get the condition you have. You could ohm test the ones you can get to today.

I will look into that! Thanks for all your help!

[thefitisgay]

theres and eec tester plug... on my 92 l6 its under the hood pretty much right under the hinge on the fender... its under a little plastic cover that says eec test plug its got a spot for 6 wires but has 5 and theres a single wire in a single connector... you short certain wires or one to ground and then when you key on it will flash codes on the cel... they also have a running test.... google eec self test... i think the sho guide is the most informative? i forget sorry for not saying this first i feel like a doosh... good luck

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oh yeah drivers side fender... doh

[thefitisgay]

here http://www.scribd.com/doc/34996350/Ford-OBD1-Codes-and-Procedure

now i dont know if it will tell you any usefull information... or if you can even read the codes it give out bcause i never could (ha) theres like 3 different periods and no real seperator between them