It runs....sorta

zzebby · January 03, 2008, 02:10:39 AM

Been working on this 71 Ford pickup for 6 months and got the 5.0 HO running tonight sorta. Spent the last 6 weeks rewiring for the A9P computor to run the MAF and all other stuff. All factory stock, but no smog pump. Did keep the EGR system.
Well it fires immediately and then quits in about 3 secs. It is running out of gas. I know this because if I switch the key on and off numerous times and fill it with fuel it runs another fews second longer. If I hold the start on when it is stalling it will still not keep running. Is the computor not opening the injectors or is it something with the fuel pressure regulator seeing vacuum and then dropping the pressure too low?
Injectors can't be clogged with old gas could they as it always starts ??

wayne petty · January 03, 2008, 03:05:22 AM

does the fuel pump continue to run once the truck starts... you might try a hot wire directly to the pump to see if that will let it run... the ecm only powers the fuel pump for 2 or 3 seconds as soon as you turn the key on to charge the fuel rail...

it depends on a differnt circut toget the ecm to continue the power to the fuel pump relay, main eec relay and the fuel pump...

this link should be close to what you have look at figure 6....

http://www.autozone.com/az/cds/en_us/0900823d/80/19/59/5a/0900823d8019595a/repairInfoPages.htm

when you look at it.. both the fuel pump relay and the main relay have to be on for the fuel pump to get power.... figure 5 does not look right.... in the eec main and fuel pump relay wiring... that is probably because there was some probems in the factory diagrams in that area earlier.. made my life tough for a few hours a long time ago...

zzebby · January 03, 2008, 10:55:49 AM

Quote from: "wayne petty"does the fuel pump continue to run once the truck starts... you might try a hot wire directly to the pump to see if that will let it run... the ecm only powers the fuel pump for 2 or 3 seconds as soon as you turn the key on to charge the fuel rail...

it depends on a differnt circut toget the ecm to continue the power to the fuel pump relay, main eec relay and the fuel pump...

this link should be close to what you have look at figure 6....

http://www.autozone.com/az/cds/en_us/0900823d/80/19/59/5a/0900823d8019595a/repairInfoPages.htm

when you look at it.. both the fuel pump relay and the main relay have to be on for the fuel pump to get power.... figure 5 does not look right.... in the eec main and fuel pump relay wiring... that is probably because there was some probems in the factory diagrams in that area earlier.. made my life tough for a few hours a long time ago...

Yes the fuel pump does continue to run and then stops about 3-4 secs after the engine quits. So there is fuel being pumped to the rails. Earlier, before I had the wiring done, I had "hot" wired it direct and engine did the same, ran for a few secs only.
How does the fuel pressure regulator work?

wayne petty · January 03, 2008, 11:10:17 AM

the fuel pressure regualtor is mechanical.. probably not the problem...

warning do not use a regular test light on the circuts...
can you measure the voltage on the + side of the injectors while you try to start it..

? it should come on with the key and stay on...

also does your volt digital meter have a dwell setting or a ms setting..

and do you have a NOID light?

? it plugs into the injector pig tail and flashes when the ecm pulses the circut...

Great Neck   / 6 pc Noid Light set from autozone
Part Number:   27161
Pricing: $20.00   Normally stocked at your local store

kb426 · January 03, 2008, 01:17:53 PM

It takes that computer about 2 seconds to run it's scan and if there is a serious problem it will shut off. If you have trouble codes, that will be a starting point for diagnostics. If you have no codes, you may want to try another computer or try that one in another car to make sure it's still fully functional.

zzebby · January 03, 2008, 02:22:39 PM

It will start again if I turn off the key and do the same again. Can do this as many times as I want. Does the computor still scan? I do have "always on" 12 V to the computor.
Will pick up a noid light on the way home tonight and will borrow a meter from work.

jaybee · January 03, 2008, 02:27:50 PM

Don't know if this transfers directly but I know a guy who just about went nuts diagnosing this exact problem on an S10 Blazer. Someone had direct wired the fuel pump to switched 12v. Because the PCM couldn't tell if the pump was functioning properly it assumed that it wasn't and shut the injectors down a few seconds after starting.

kb426 · January 03, 2008, 03:09:49 PM

Yes the computer scans every time the engine starts. It scans continuously after that. When I was sorting out problems on mine, I found out about the 2 second interval. The fuel pump is run by one of the relays in the system. If you had switched power running to it that was disabled after the key was released from the start position, you would have the end result you are describing. I assume you have a good wiring diagram?

zzebby · January 03, 2008, 03:39:35 PM

Quote from: "kb426"Yes the computer scans every time the engine starts. It scans continuously after that. When I was sorting out problems on mine, I found out about the 2 second interval. The fuel pump is run by one of the relays in the system. If you had switched power running to it that was disabled after the key was released from the start position, you would have the end result you are describing. I assume you have a good wiring diagram?

The fuel pump relay is on switched power, but the computor has both always on and switched according to the NUMEROUS wiring diagrams that I have. That is a sore point. I must have a half inch of printouts that I'm working with. Most are the same, but minor little things are different and they say for a particular year of Mustang 5.0. The computer is a A9P and yet I don't know what year it is other than 87 to 93 or so. (Ebay). I had to make up the harness from two or three other harnesses as I have components in non std locations and am running the MAF on the inlet. Tonight I'll try the noid light' as Wayne suggested, and see if the injectors are staying on. If they are not then what

New computer??

GPster · January 03, 2008, 04:03:41 PM

Just one dumb thing. Someone mentioned about the computor seeing momentary power interruption and shutting down in 2 seconds. Are you using the original truck ignition switch? Does it go from Start/ Ful power to coil to Run/resisted power to coil like old time (before HEI) GM system? I spend a lot of time convincing myself that I'm wrong. GPster

kb426 · January 03, 2008, 06:27:17 PM

Zzebby, if the computer will retrieve codes and all the relays work, I don't think it's your problem. If you can be positive that the computer is ok by spitting out any codes at all even though it hasn't run very long, it will be very helpful. Do you have a " check engine light" in the system. When mine was hosed, the light would come on right before it shut down.

zzebby · January 03, 2008, 07:13:20 PM

The truck ignition switch is not yet in the wired system. I'm holding the harness that goes under the dash (all new that I've wired) and have not yet hooked it to the key switch. Just touching wires together to start / run.

I do not have a check engine light and don't see it on any of the schematics. I do have the MAL function connector wired in. It is same an all wiring diagrams that I have so it must be correct. I do not have a code reader for it. Next thing to buy..... So don't know if it is showing any codes.

kb426 · January 03, 2008, 07:23:39 PM

I bought a code reader at one of the chains for around $30. I'd plug it in abd see what's there before I went any further. I bought part number 3145 from OReilly's. Just read the instructions before using. In case you haven't been to these websites, they have lots of info.
http://www.fordfuelinjection.com/
http://www.geocities.com/motorcity/flats/3349/codes.htm

zzebby · January 03, 2008, 11:38:03 PM

OK now I'm really wishing I'd done something different.
Tonight the fuel pump runs non stop, whenever the key is on. Last night it worked properly, ran 2-3 secs when the key on and then stopped. It just sat all day..........no one around. And it doesn't really start now. It will fire once when the key first turned but not really run like it did last night. Bought the noid light and yes the injectors are opening, light flashes bright. Checked the spart at the plugs and good there. So it's got fuel (injectors opening), spark, timed what gives???
I have an extra computer but it it is a speed density AOD2 , can I try it just to see if there is any difference?
Next will buy a scanner and check the codes. Or has the computor died and that is why pin #22 of the computor is grounding the fuel injection relay all the time??

wayne petty · January 04, 2008, 04:37:25 AM

did anybody back probe the system with a test light?>>> the transister driver in the ecm blows out at 1 amp.... sometimes using aftermarker relays without diodes to dampin the high voltage spikes that can be generated when the ecm opens the circut...and the magnetic field collapses in the relay....

are you anywhere near los angeles..

i have several eec 4 break out boxes... got a otc at a swap meet and a rotunda from a scrap truck where a ford dealer threw it out...