RPetty_43

1993 F150 5.0L EFI 3spd Automatic w/OD

Has anyone heard of the fuel injectors causing a back feed situation with the ECU? My understanding is that the TFI module controls the ignition until it starts. The the ECU takes over and signals the TFI. I've exhausted all other possible components and even gone so far as to turn off the fuel pump and manually fed fuel to the engine. It will not start and everything points to the ignition, although a strong spark exists or seems to outside the combustion chamber. This is the first engine I've ever run into where I have compression, fuel, and perfectly timed spark and can't even get a flicker of hope.

dirttracker

i have same problem,did you figure it out?

RPetty_43

Rather than pull the wiring harness apart or buying a new one for more money than the vehicle is worth, I simply installed an all-in-one distributor for $80. The truck fired right up. The problem was that distributor is quite a bit larger than the original and did not allow the drivers side fuel rail to fit. Long story short, I installed a carb and manifold combo and all is well. If you can find a smaller diameter all-in-one distributor, that would be the route I'd go if I had it to do over again. In the end I believe the EFI functioned well. As always, the fault was on the ignition side, though it may have been some weird feedback issue from the EFI wiring causing the ECU and/or TFI to go haywire. I've never seen anything like this problem and had stumped several Ford technicians along the way. So rather than spend a couple thousand dollars to make it as per original, I chose to spend approx. $300 and will sell the handful of new/used Ford TFI parts on eBay. TFI stands for Terrible F'ing Ignition. The whole PIP signal to bank fire the EFI and at the same time fire the plugs makes the work around a challenge. A crankshaft sensor, if it were a Hall Effect sensor, may also work if you were clever and had the parts. I thought about it, but could never find someone with a wiring diagram of just how the TFI/EFI/ECU worked in concert. I'm pretty sure the Disty sends a signal to the TFI, which fires the coil and sends a signal to the ECU, which fires the EFI circuit. The Disty signal to the TFI is a Hall Effect signal, not sure about the TFI to ECU signal however. Logic says Hall Effect, but this is a Ford. And again, it was too costly for my old dump run truck.

icu1954

buy a used ecm and try that,that could be the culprit.

RPetty_43

I was on PCM #3 when I ditched the whole system. Jegs intake, Edelbrock carb, and an HEI disty solved this electrical mystery. She purrs like a kitten.

jerryclanton

This thing driving me crazy ,,stop like it was"nt getting any fuel,,,waited about 10 mins turn key on heard fuel pump started it up drove about 3 miles it stopped again waited 20-30 mins turn key on fuel pump started again,this time I drove were I was staying 5-6 miles replaced fuel filter it had all kinds stuff come out ,been 18 years sense I changed it,,i started it let run for 30 mins,, .the next day started right up and drove 5-6 miles this country i'm talking about Shelbyville ,tn was trying head home from my ex's it stopped never started again had it towed,back her house put new puel pump, didn't work checked firing no fire chaned ignition control module no good changed the coil no good ,put in new distr. no good this no fire,,,only thing I know is new ECM,but trucks in tn and I'm in Alabama,will ECM out of 93 work someone said I had had the numbers off the old, that be hard do,, any help ,I would be verygrateful

icu1954

try another ecm,it worked for me.If ecm is bad you won,t get fire or fuel.I don,t know if a 93 would work but i think if it came out of a vehical with the same engine and transmission it would work.Good luck

RPetty_43

If the usual diagnostics don't work, go old school. The old OBD1 systems are outdated and if you have some odd back feed or buried short somewhere in the harness, it can be frustrating. I think I'd rather spend the money on a complete update to OBD2 and perhaps SEFI if I went the much more expensive route of replacing the harness and all components and sensors. After removing all the vacuum controls that are tied in with the sensors on my little 302, I wondered how the engine found enough air to run.... With my current setup, if I decide later to upgrade I may install a reasonably priced after market self-tuning EFI carburetor.

Chris_1

iTrader: (1)

You don't say what motor you have but if it's a 302, a 93 won't work on a 94.
You should check (or have someone check) the fuel pressure. Some fuel pressure isn't good enough, you need the right amount of fuel pressure.

RPetty_43

VIN number should do. My 1993 had all the needed info on the door pillar. Take a photo of the decal with your phone. To replace, simply connect the new ECM to the harness connector without removing the old ECM. If it works, then you can remove and replace the old ECM. You will need to loosen the inner fender to get it out.... The ECM or ECU or PCM, as Ford calls it, controls more than just the engine and needs to be matched to the transmission. Hence the need to match the old PCM. Advance Auto is a good source.