Wouldn't post if I didn't really really need the help. Anyway, 90 F-150 302. Ran rough for awhile, did a completed tune up on it. While searching for the fix to the rough idle, random stalling etc. I now can't get the truck to even start. It turns over, good spark from coil visually verified the spark coming from the coil pack. Fuel pumps come on with either tank selected. Sometimes, when the key is in the on position the fuel pump will continue to run and you can hear the relay clicking. (Changed relay) no better. I've messed with the inertia switch. Here's where it gets weird. I get better results with the switched tripped to the off position when I try to start it. It will actually turn over for a min than die like its supposed to. I turn the switch back on and it won't turn over. I've tried spraying starter fluid in the TB and it won't even start with it sprayed in the TB. I'm thinking something in the ignition sequence is either grounding out or at fault. Just looking for a good place to start if you were in my shoes. In my sesrchings I've come across possibly suspecting the PCM but that's a 150 part and I'm not made of money unfortunately.

No start, turns over
I can smell fuel ( not sure of pressure)
Won't start with starter fluid being sprayed in TB
Thanks for your help fellas

 

have you checked injector pulse with a noid light or test light. when the fuel pumps stuck was your battery low before you test anything verify your system voltage at the battery and were your meter is connected. you need exact fuel pressure as these trucks will not try to start with low fuel pressure. did you check for a weak spark how far did the gap jump. PCM is only one of many problems it could be. checked any fuses. is your ignition system an engine stock. what did you do tune up wise did this happen right after any particular repair. sorry for the questions but they should give you direction. so it will not crank with the fuel shut off tripped.

 

So when u did the tune up did you check compression? Timing Chain? Even if u have all the right inj and ign pulse still need bout 3-4 inches of manifold vacuum cranking.


Ron C. near Pleasant Plain Oh.

 

So when you trip the inertia switch it starts and runs for a minute, How about the fuel pressure regulator? pull off the vacuum line and see if fuel comes out of it. make sure your return line is not pinched or plugged, sounds like too much fuel. Insto floodo. do you have a fuel pressure gauge?

 

carguy:
i did not check compression. it was running great when i bought it. i only did the tune up because i wasn't sure when the last time it was done. i did plugs/wires, fuel filter, cap, button. it ran good most days after that, it was a hit or miss issue.

i have not checked the timing chain because it would run, when it did run it would have no issues. it was just intermittent.

yes when the inertia switch is tripped it will start, for a second or two. when its not tripped i get NOTHING at all. i pulled the vac line and there was no evidence of it leaking. can i just crank it and see if fuel comes out of there?? i do not have a gauge, i need to find one this weekend just so i can rule out fuel. but like i said it first post i can smell fuel. the more i try to crank the stronger the smell. the only reason i suspect pcm is because of what i found on here. would love for it to NOT be that however. im going to throw a good coil on it in a few. ive read that if you disconnect the PCm and spray fluid down her throat and it starts...it leans more towards a pcm issue. maybe the pcm not grounding the injectors...but when i tried eariler with the starting fluid i was sure that it would start...essentially im giving it fuel with the fluid. so the only thing it would need would be spark....in a perfect world...about to go work on it now...will post any findings..

thanks for all your inputs, it really does help and i appericate all you time!

 

The fuel pump should run for only a second or two when turning the key to the Run position. One cause could be a sticking relay, but you have eliminated that. The next MOST likely cause is a bad PCM. This is a VERY common failure mode.

Save yourself some time, pull out the PCM, open it up then inspect it for signs of leaking capacitors or burned components.

 

if you let the engine sit and cold start it will it try to run or fire at all have you tried putting your foot on the floor while cranking. checked codes yet.

 

yes it has sat for a few days...cold and it will crank but not turn over. i just checked it with a good coil and still no luck. as soon as it stops raining im going to pull the PCM and take a look at it. that's just behind the pedals correct? i can see the harness on the engine side firewall but cant seem to locate it inside the truck...am i not bending properly....lol

thanks again gents

ill post findings with pictures here in a little while

no CEL, and no codes, however the battery has been disconnected multiple times so that might of rest the pcm...?

 

From Subford:


Your model year truck the PCM comes out from the inside. You will have to disconnect the connector on the firewall side.

 

thanks subford. got it out, opened it up...NOTHING! looks good, no caps leaking. however i may of found a short, no idea on where to even start with trying to find that..any suggestions and or tools to assist along the way?

 

what do you mean short. in a wire or in the pcm. a short usually a test light and a volt meter on continuity and a small amp gauge with a needle. by the way I see in your post at the top it says stationed are you in the military hope its not rude of me to ask just wanted to say thanks if you are.

 

ya i have a friend over here with his multimeter. not in the pcm, we just took it out to take a look. and it did start with starter fluid for a little while like 20 sec than died of course because of the whole no power to fuel pump thing. hes getting readings from his meter with the battery out and the KO. i dont remember what those readings were exactly. but i do know they got higher when we disconnected the alternator. ill have more details here shortly. were comparing readings from his vehicle. im still sticking to the possibility that something is grounding/shorting out somewhere which is causing these issues..

and no its not rude, it is my pleasure

times likes this i wish i worked in vehicle maintenance!!

oh well

 

ok so ive made some headway. we figured out that my injectors keep firing. even before the key is in the start position. flooding the engine causing it not to start. when we remove the fuel pump relay and cut off fuel it will crank and run until that fuel is cleared out. so now were thinking either PCM not send the correct signal OR something to do with the ignition switch, possibly sending the wrong signal..progress, not much but progress.

any thought?

 

are you sure they were firing if so that's not good news for your engine computer. im sure you know they were but just to be sure how did you test that. this should have nothing at all to do with the ignition switch.

 

We actually felt them firing. Which would explain why it would run when the kill switch was activated. It wasn't getting flooded and now I just need to figure out why.....we looked in the book and determined the crankshaft position sensor which sends a signal to the PCM. But we can't find it to even test it. Do these 302s have a crankshaft? We can't find it anywhere...