I'm using APYP, modified just a hair so far.

Problem I'm having is that the vehicle will only start when it's not been run for a day or so.

I've narrowed it down to ignition wiring, but fuse panel/ignition switch area. The switch is good: disassembled, cleaned, did the same for all the connectors and terminals. First start of the day, no issue. Once engine temp starts to rise, if I shut it off, it won't start.

I tested, and if I run the injector feeds directly from the battery, it will start everytime.

There unfortunately isn't much I feel I can do to fix the wiring issue without ripping the entire fuse panel apart, and that would be close to my last option. It's doable, but just not something I'm looking forward to.

I'm curious though, that since this is a voltage issue, could I play with the injector pulsewidth correction vs battery voltage table a hair to see if the problem could be compensated for? If it works great, if not, nothing lost,. right? I notice that in the stock table, the "usec added" value changes from 8V to 9.6V, and 9.6V is roughly where the voltage difference in my situation exists. Just under 9.6V and she won't start, over that (direct from battery while cranking) it will start. I'm looking at the lowest battery reading here, thus why 9.6V, that's just the momentary voltage when the starter is first engaged.

AmI way off in thinking that I might be able to compensate for the small voltage difference with this table?

 

You stated that if you jump the injector feeds it will start. Are you getting power to them without a jumper?

If there is no oil pressure detected, the ECM wont power the injectors. Also, on a friends 85 vette, occasionally he would be stranded when his car would act up. It never had a code stored. I drove it for a while, and found that his TPS was bad. It would return a signal to the ecm indicitive of WOT when it wasnt at WOT. This enters the ECM into "clear flood" mode, shutting down the injectors.

Just some food for thought.

As for the bat voltage vs pw that makes global changes not just start-up changes I believe.

When you say the car wont start- does it turn over with the starter and just not fire?

 

Yep. Starts up and runs fine first thing in the morning. New battery (old one couldn't handle the troubleshooting I was doing lol) and the injector feeds get power as they should. Turns over no problem, spark to the plugs, all sensors in range, all relays etc working correctly. (as they should, since it does run) The injectors do NOT pulse when it won't start. All grounds are new and clean, (essentially just installed the engine and the harness) but as one of the things I'm going to try, I will doublecheck all of them.

There isn't an issue with something not working right in the system (oil pressure, etc) as feeding the injector leads and it starting means that everything else is ok, it's JUST the voltage the injectors are seeing is the problem, as I see it anyways.

I've done every test I can think of, the only thing that I've found that "solves" the no start condition is providing a hair more voltage to the injector leads.

I've still got a couple more things to try, but it seems strange that this issue is so narrow in the voltage ranges that cause problems, and that range coincides with the PW/batt voltage table "breaks".

For a little more history that may or may not be pertinent, this problem was slow to come on, until now where it is 100% consistent. It wasn't like there was no problem, then all of a sudden there was, it gradually just got worse. Changing the ECM with known good one does not help.

 

Maybe the problem is on the other side of the circuit.
Try running a new, separate ground wire from the ECM to the battery. Maybe the ground path from under the dash, cyclinder head (or wherever the ECM ground goes) is not getting to the battery as well as it should. The extra voltage may be able to overcome the resistance of the ground path right now.
Worth a try anyway.

SBNova, Are you sure injectors won't fire if no oil pressure?
I've never heard of that, although I'm not familiar with 6E.
I do like the idea though and may implement something along those lines in my setup.

 

The injectors will fire with no oil pressure. Oil pressure switch exists only to bypass the fuel pump relay if it fails.

Wiring schematic for the fuel pump setup is pretty widely available, the oil pressure switch is wired in before (and "around") the fuel pump relay, but if the relay is working, power is supplied to the fuel pump regardless of oil pressure.

I will try the ECM ground idea, that had been kicking around my head earlier but I forgot about it.

 

I knew the wiring but questioned the code to do that.
Cool idea to try though.

 

Is VATS still enabled?

 

Nope, no VATS.

Even when I go back to the 1987 ECM/PROM it does the same thing.

Grounds have all been re-checked, all are good. Problem is either across the ignition switch (which is good: disassembled and cleaned, along with all the connector terminals) and/or the wiring (which is nowhere near easily fixed) from the ignition switch to the fuse panel, which is the last thing I want to deal with.

I'm dealing with a 1987 MAF setup, just using 6E.

 

You might want to try a spare fuel pump relay. If it's getting old, it could be having problems transferring the juice when everything under the hood warms up. I had the same problem and it turned out to be the fuel pump itself. Went ahead and changed the relay while I was at it........

Wouldn't change a setting to compensate for a non tuning issue. Unless of course it's your only ride like mine was at the time..... If you have the stuff, datalog while driving and see if you are going lean and then rich. Could be indicative of a pump getting weak or the EGR valve sticking open.

Another thing to check is the routing of your existing wire from your existing relay. If it is close to an exhaust pipe, reroute it away from the heat source. (Does heat soak on a 3rd Gen starter sound familiar anyone? Same principle.) You might even want to run a larger wire while you are at it.

Since your problem seems to go away with a direct jumper wire from the battery, I would suspect the relay is bad. Try wiring in an auxiliary relay directly from the battery. If you decide to install another relay to the fuel pump try running a 10 gauge wire from the battery (so you don't lose so much voltage with the distance) to the relay which should be mounted near the gas tank. Use the original wire to the fuel pump as the trigger for the new relay. It takes very little voltage to pull in a relay....

 

Fuel pump relay or ECM. I think what happens is when the relays go bad they work when cold then crap out after a while. Since the car is running the oil pressure switch bypasses the relay so the car does not die on you when you are driving. The easy way to check is to do this: when the car does not want to start crank it like an old carbed car that is flooded. You don't have to gas it though. When the pressure switch kicks in the car will start. IE this is a hard start symptom. Most guys are so used to the turn and start that they don't even think of this. BTW if you every buy an aftermarket harness do not get a fly by night one without the pressure switch. Ask me how I know.

 

Back from the dead, but just a closeout:

After having to wait over a year to work on the problem, update here so no one needs to read MY portion any further, other than to understand what was going on.

Went and got a new to me ECM. Replaced, problem gone. Got my new Ford injectors installed, sold my old stock ones, buyer had them tested, 3 of the 8 were "dead". Decided to install my "dead" ECM, and see what happened. Sure enough, problem no longer occurred. Go figure. Problem solved, bad injectors!