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Discussion Starter #1 (Edited)
Warm Start Issue (RESOLVED)

I've been experiencing a warm start issue for a little while now, and I'm not quite sure what's wrong. The car will start with no problems when it's been sitting for a little while (ECT could read 70 F or 180 F, and it makes no difference), and once the engine is running, everything seems fine. However, if I drive for at least 5-10 min, shut the car off, and try to restart it, it struggles. Sometimes, it kicks once, and I can save it if I open the throttle, but I often am not so lucky. I've also been getting terrible gas mileage around town, so I wouldn't be surprised if it's related. Typically, I only drive ~10 miles a week, and my last two tanks were 21-22 mpg. If I drive on the highway for a while (~200 mile trip), I'll get 32-35 mpg, which is what I normally get.

I just installed a new main relay, tried a spare set of injectors, and I have spark. The spark plug wire resistances seem reasonable, the plugs and air filter have ~750 miles on them, and the fuel filter has ~2000 miles on it. The fuel pump primes all the time, but I have no means to check the pressure.

The engine is a d15b7 with a d16z6 head, intake manifold, and ECU.

Could the spark be too weak to start the car when it's warm? I'd think it would be the opposite, unless the engine heat is affecting the coil or ICM.

Any ideas?

Thanks,

Dan


EDIT: Forgot some information - no CELs, and the IAT and ECT readings are reasonable.
 

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i had the exact same problem.. i had to unplug the sensor on the fuel rail that comes from the charcoal canister. try that and see if it works..
 

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Discussion Starter #6
i had to unplug the sensor on the fuel rail that comes from the charcoal canister.
I just checked, and I don't have a sensor on the fuel rail that leads to the charcoal canister. The charcoal canister has three lines: one to the throttle body, one to the EVAP purge solenoid, and the other leads somewhere else, wherever the fuel return line goes. I tried unplugging the EVAP solenoid, but that had no effect. Am I missing something?

danz, I haven't had a chance to check the wiring yet.



I have noticed something weird with my ECU though. I have a switch on J1, and if I flip the switch when I have this problem (to cut the connection), the car will start. However, the idle is high (12xx rpm), it's rough, and the car shakes as though it's misfiring. The CEL is also on when I do this, but when I jump the service connector to check the code, I get a solid light.

However, as soon as I flip the switch again, the car will start (albeit weakly), the CEL will be off, and the idle drops back to normal. I can then drive the car, and everything seems fine. The only weird issue that I sometimes have is that I randomly get CELs for the oxygen sensor, oxygen sensor heater circuit, and ELD. I have an LC-1 wideband used as a narrowband sensor, and the oxygen sensor heater circuit is disabled in my ROM. I only have this issue when I flip J1, and if I start the car normally, the oxygen sensor warms up right away, and I can see that it's working (or so it seems).

Could some IC on the board have a problem and ONLY cause this issue? I guess it's possible, but it seems extremely unlikely to me. I have my original P06 ECU, so I can try that tomorrow.

Any thoughts?
 

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Discussion Starter #7
It looks like the problem is ECU related. I just drove around with my original P06 ECU, and everything worked fine. There was a trouble code for the oxygen sensor heater circuit (as expected), but nothing else seemed to be malfunctioning. After the car was warm, I tried turning it off and restarting it. The engine consistently started within 3 cranks, the CEL was off, and the idle was normal (if not better).

I don't know if there is a problem with one of the ICs or if I have a bad solder joint, but something is obviously screwed up in my P28 ECU. Unfortunately, school will keep me busy for the next few weeks, so I won't have much time to diagnose this further. I'll look into it more at the end of December.

Thanks for the replies.
 

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This is not really my area of expertise so I would really like to be corrected if I am wrong so I can also learn from this, but it seems like it is over fuelling at idle for whatever reason. Leaky injectors, excessive fuel pressure build up, overheated fuel rail or injectors on hot soak or ECU programmed to provide to much fuel at idle for whatever reason.

Does it blow a puff of black smoke if you get it to start hot.

As it changes with the ECU, it seems the problematic ECU may have been chipped to excessive increase idle fuel with your engine and injector set up.
 

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Discussion Starter #11
I've been watching for black smoke, but I haven't seen anything. The exhaust does smell a little like fuel though. Since I have spark, it has to be mixture related, but I'm not sure about the details.

I'm running (or at least, I think I'm running) a stock P28 map right now. The only changes were: adding the Crome datalogging routine, disabling the oxygen sensor heater circuit, and removing the checksum.

It's weird because this problem occurred all at once. One day I could start the car with no problems, and the next day, I'm wondering if I have to call AAA. I made no changes before I began having this problem, so it's a mystery to me. Electrostatic discharge maybe? Solder fatigue? I dunno.
 

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Discussion Starter #12
So it turns out that my issue was tuning related. I must have loaded a different ROM and forgot to change it back. Then, I must have never tried starting my car (while warm) for weeks, and that's why the issue seemed spontaneous.

I had different cranking and warm-up fuel curves, but everything else was the same, which explains why the car was fine once it was running. Since I hadn't changed the ROM for a while before I started having this problem, I never thought to look. Oh well.

Thanks everyone for your input.
 
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