Strange No-Start Condition

fastsc92

Registered User
Just got my car back on the road again after a few years and recently I've had a no-start condition that is confusing me.

The car runs and drives like a champ 98% of the time. However, there is a strange no start condition that I can't figure out. If the car has been running and I go into a store or just turn the car off for a short amount of time, ocassionally, it wont want to start or idle, and smells like raw gas when cranking. This is confirmed when the wideband reads 10.0 on the display. If I reset the battery for a few minutes and try it again, all is good.

I did notice something strange when this occurs. When I have this no start condition, my datalogger will not work. The wideband has a stand-alone display, but it will not transmit any signals to my laptop. Upon further inspection, if I probe the wires used as signal taps into the logger such as MAF, TPS, ACT, etc....all read a voltage of 2.15V from the ECU with the key on engine off.

Once the battery is reset, signals read normal, the logger works, and the car starts up without any issue. This doesn't do it all the time, it's hit or miss when this no-start issue happens.

The car has an EEC tuner board, and a PLXwideband/datalogger. All signal taps are made at the ECU harness, soldered and heat shrunk, and a 5amp fuse is installed in series to the unit. The fuse never trips, so I'm assuming the logger is not the issue especially if the computer is outputing 2.15 volts on those specific signals.

The battery is in the trunk and the grounds are good, and I can't see any issues from that area. This is really the only change that I've made since before the car was running fine. I've used #2 welding cable for the main power, grounded to a solid point in the trunk, cut-off switch is breaking the positive coil wire.

I'm out of ideas on this one. Would a bad connection at the tuner board cause this issue? A bad ECU? Is the cut-off the culprit? I used 16awg to run the coil signal to the switch. This may be too small of a guage, but it doesn't explain why the computer would have a strange output and no-start. Any ideas or comments??
 
Had a very similar problem several years ago on warm restarts...by accident I found that if I let the car idle for about 45-60 seconds before touching throttle or putting in gear, it ran fine. I'm thinking it may have been the amount of time required to go from open to closed loop operation. I thought that was an indication that there was way too much fuel enrichment on the start up portion of the tune.

Never did find out exactly what the problem was, but it went away when I switched to an SCT chip and new tuner.

David
 
I did notice the other day that it was running fine, started normally, and right after I started it (20 sec or so) I reved it and the car revved up, then immediately died. Then the no-start condition happened.

I'm not sure that this is the case every time, but I'll try it out later and see if the same thing happens. It's just strange that the ECU outputs all read 2.15volts until I reset the battery. I don't think its a tuning issue. It's almost like the computer is taking a dump on me....
 
I had that problem before. I read before speculations that due to the engine being so hot it vaporizes the fuel on the fuel rail. Not sure if that a myth or not. But if you keep cranking it flood the engine with fuel and not start, Press the accel down to cut off fuel if you are experiencing flood "smell of gas".
I have not had these issues after the tune though so not sure if thats related.
 
I feel that it's not tune or hot start related, since the computer outputs bogus sensor values durning this no-start cranking. The TPS, MAF, ACT, ECT should not output 2.15volts when not running. Plus, it doesn't do it all the time. It did do it at the track once during tech-in, and a few times the days following. It's been good for the past day.

I used to have a hard time cranking before but it was leaky injectors.
 
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Just a Thought

Is it possible that the heat induced by the various soldering operations may have stressed an interface or other component. I guess it's dependant upon the use of a heat-sink and the proximity of the heat source to the unit. Are you able to run a self-diagn osis on the unit ?
Just a thought.
 
it was doing this before when I had wire taps. I thought that may be the issue so I soldered the connections instead. Still with the same results, again, random. I'm going to try to check the tuner board connection and see if it is loose.
 
I had that problem before. I read before speculations that due to the engine being so hot it vaporizes the fuel on the fuel rail. Not sure if that a myth or not. But if you keep cranking it flood the engine with fuel and not start, Press the accel down to cut off fuel if you are experiencing flood "smell of gas".
I have not had these issues after the tune though so not sure if thats related.

That is 50% true. It's called vapor lock, but is really only an issue for carb'd cars.

As to the original post, did you do a tune-up? New fuel filter?
Since the electronics are acting wierd, try checking for KOEO and KOER codes also.
 
no codes are present on either test....

I highly doubt a tune-up would cause this, but regardless, there is a new fuel filter, the air filter is clean, plugs are new, fuel is fresh
 
The voltages you saw were interesting. So the engine cranks, motor spins, but no fire? See if you can check the voltage going out to the sensors to see what goes out. I'm wondering if the DIS or coil pack is pulling down the voltage.
 
Out of curiosity, watch your boost gauge everytime you shut down. Normally the gauge will creep back to zero after shutdown, but see if it suddenly snaps back to zero when you shutoff and then you have the starting issue after.

Frit

ps I explain more if this is your case.
 
The voltages you saw were interesting. So the engine cranks, motor spins, but no fire? See if you can check the voltage going out to the sensors to see what goes out. I'm wondering if the DIS or coil pack is pulling down the voltage.


Engine cranks, motor spins, it'll hardly run, running richer than a 10.0 ratio. The sensors ( at least the 3 I tap into..) add read 2.15volts going into the ECU. Again, once I reset the battery for a few minutes, it'll fire right up, run like a champ and wont do it for a while.

I'm wondering if the battery-cutoff has anything to do with this. I'm cutting the 12v coil wire, which is run all the way to the trunk, and back up front. I can see it may be causing the no-start issue, but it doesn't explain the sensor outputs.

I'll take a peak at the vac guage next time I start it.
 
Shutdown, not startup. The reason I'm saying this as ever since I installed my cam, once in a blue moon the car struggles to start and I actually have to hit the gas to rev it up to catch. In these cases the car is VERY rich and it blows black smoke when it starts.

I just happen to notice one time my boost gauge snapped to zero when I shutdown, and when I went to restart it wouldn't.

Now I've noticed everytime that gauge does that, I get the starting problem.

Frit
 
I'll give it a shot....I meant next time I start it...I'll see what happens when I shut her down.

I think something it up with the computer or tuner though
 
no codes are present on either test....

I highly doubt a tune-up would cause this, but regardless, there is a new fuel filter, the air filter is clean, plugs are new, fuel is fresh

So the tune up and diagnostic bases are covered. I have seen Fords on no start set unrelated codes or none at all.

Anyway, how is the voltage to the sensors? 12v I assume. Sounds like a PCM or chip getting ready to meet its maker.
 
The TPS, MAF, ACT, ECT should not output 2.15volts when not running.

Correct, of course.

IME this sort of thing has been due to a problem in the Signal Return wiring. You have the 5v VREF, the Signal, and the Signal Return which could be considered ground. When the Signal Return has high resistance it results in a high reading on the Signal circuit, frequently about half the VREF value. Also, typically the ECT, ACT, and TPS are all spliced together and use the same Signal Return pin on the ECM.

So the next time you can try get it to have the problem it would be nice to have probes rigged so that you can check voltages on the Signal Return (black) under the hood and at the appropriate pin on the ECM. That way you could determine if harness, ECM, or ECM to ground is the issue.
 
Correct, of course.

IME this sort of thing has been due to a problem in the Signal Return wiring. You have the 5v VREF, the Signal, and the Signal Return which could be considered ground. When the Signal Return has high resistance it results in a high reading on the Signal circuit, frequently about half the VREF value. Also, typically the ECT, ACT, and TPS are all spliced together and use the same Signal Return pin on the ECM.

So the next time you can try get it to have the problem it would be nice to have probes rigged so that you can check voltages on the Signal Return (black) under the hood and at the appropriate pin on the ECM. That way you could determine if harness, ECM, or ECM to ground is the issue.

Where is this black wire located under the hood? Are you talking about the grounding wire for the computer that connects to the battery? If so, since the battery is in the trunk, I located that ground to the same position on the frame rail up front with the original negative battery cable. The battery is grounded to the frame rail in the trunk.

It sounds like we're getting somewhere here.... I'm assuming that the signal return should be the grey/red stripe on the ECU harness. Such as in pin 6...
92' Wiring Diagram
 
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I think on the '89/90 cars it is a different color (Maybe Black?) and least on the '91's (maybe up to '93?) it is a Grey with Red tracer that goes to Pin # 46..

We had someone local here that had a weird issue with their car (forget truely, but the CEL always was on and ran oddly?? and you couldn't pull codes from the EEC)
Grounding the Signal Return Lead corrected everything.. CEL went off, able to read codes, ect...

the Signal Return Lead is also at the EEC Test connector??
 
Now that I think of it....At one time, I used one of those cheapy wire-taps to tap into pin #6 for a reference ground( The kind that pinches the wire). It has since been removed but maybe that wire is damaged at some times and messes up the reference. Strange while it does it during starting only. Def. something to look into. I've been sick the last 4 days so I haven't been able to try anything out on the car. Repairing that wire will move to the top of the list of things to do. Great input guys
 
Note that the sensor ground is tied to the DIS module ground which is through the bolts that hold it to it's mount. It flows through the harness that runs along the side of the blower and connects the DIS, Cam, Crank and coil pack.
 
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