injectors over heating?

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injectors over heating?

Postby yellowlt1ta » Sat Aug 04, 2012 10:54 pm

I have a 93 trans am with a 350 lt1 and a bw S480 turbo. Ms2 3.57. the injectors are 96lbs low impedance injectos and when I drove it it drives fine untill it turns off out of no where and does not want to turn back on untill I let it sit for a while then it turns back on. Im thinking its the injectors but I would like for you guys to take a look at my data logs and tell me what you think.
2012-08-04_20.1nostart8.09.msl

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'93 Trans Am LT1 80mm turbo
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Re: injectors over heating?

Postby billr » Sun Aug 05, 2012 10:41 am

That log shows a couple of cranking tries, when it wouldn't start? The obvious thing to me is that no rpm shows, is that normal for a "fuel only" MS2 system? I would think not, that your problem is with the tachin signal... without it MS thinks the engine isn't rotating so fuel (and spark) pulses would never be commanded.
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Re: injectors over heating?

Postby yellowlt1ta » Sun Aug 05, 2012 1:01 pm

billr wrote:That log shows a couple of cranking tries, when it wouldn't start? The obvious thing to me is that no rpm shows, is that normal for a "fuel only" MS2 system? I would think not, that your problem is with the tachin signal... without it MS thinks the engine isn't rotating so fuel (and spark) pulses would never be commanded.


Your right, I did not notice the no rpm signal at all. I guess I was so caught up on other possible problems that I must have over looked it. the strainge thing is that the engine shuts off while driving then will turn back on once its cooled down some. could this possibly be the ignition coil overheating?
'93 Trans Am LT1 80mm turbo
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Re: injectors over heating?

Postby billr » Sun Aug 05, 2012 1:47 pm

I doubt it is the coil itself. I'm guessing there is a VR or Hall sensor in the dizzy, that triggers the driver for the coil and provides the "tachin" signal to MS. I would start checking at that sensor in the dizzy or wiring to/from it.
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Re: injectors over heating?

Postby yellowlt1ta » Sun Aug 05, 2012 3:42 pm

I have the megasuirt for fuel only and the stock ecu controls the ignition. The tach signal is being tee'd off for the MS. the distributor is an MSD Optispark and fairly new. Ill check the wiring and post back.
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Re: injectors over heating?

Postby billr » Sun Aug 05, 2012 4:57 pm

The next time it dies and you have to "let it sit for a while" for a re-start, crank it and check for spark. No spark then would be another big hint that it has something to do with the dizzy sensor. Might help you figure out if it is the sensor or wiring from it to MS; I'm going to assume for the moment that it isn't the MS tachin circuit itself, as that is least-likely to fail.
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Re: injectors over heating?

Postby yellowlt1ta » Sun Aug 05, 2012 7:39 pm

I checked the wiring and it all looked great. I made a change to the coil because the coil and coil driver are together and they are bolted on to the cylinder head. I figured the heat from the head and turbo that sits next to it, might be overheating the coil driver. I added some washers to make a gap between the head and sensor and took the car for a ride. It has not turned off yet. I even got the car under boost a few times and then let it sit so that the heat can soak in while it was still turned on. so I hope that was the problem.

If during more testing the engine turns off I will check the spark like you said.

Thanks for all your help Billr.
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Re: injectors over heating?

Postby billr » Sun Aug 05, 2012 8:38 pm

Does your MS get its tachin signal from the output of the coil driver? If so, then that driver getting hot could very well be the whole problem. I was thinking the MS was triggered, along with the coil driver, directly from the dizzy sensor; sorry if I got you "out in the weeds" a bit. Still, checking the spark if it craps out again is an easy and valid test.
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Re: injectors over heating?

Postby yellowlt1ta » Sun Aug 05, 2012 11:28 pm

Yea the MS gets the signal from the coil driver because im sharing the signal for the stock ecu. The MS is set up for a trigger but I havent invested in a vr sensor and wheel so its used for fuel only.
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Re: injectors over heating?

Postby yellowlt1ta » Tue Aug 07, 2012 1:13 pm

so I took it out today and its hot out id say about 90* maybe more. I got to the store and when I got back I tryed to turn it on and no start. I checked for spark from the coil and no spark. so I keept the hood open and turned on the fans for a while. also took the coil driver out and let it cool down outside the engine bay. within 10-15min the car was runing again. so trying to cool it down helped get it turned on much faster.

Im going to relocate the coil driver and see if it helps. also check the signal from the distributor to make sure its not that.
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Re: injectors over heating?

Postby yellowlt1ta » Tue Aug 07, 2012 8:07 pm

I just relocated it to a cool ventalated area so I hope it works fine. Tonight I took it out for a drive and seemes fine. Tomorrow I will take it out for a long drive and see if that worked.
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Re: injectors over heating?

Postby yellowlt1ta » Fri Aug 10, 2012 8:11 am

Same problem except this time it never wanted to restart. sat for over one hr, also had new coil driver (ignition moduel). I even switched the sensor when the car didnt want to start and still nothing.
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Re: injectors over heating?

Postby billr » Fri Aug 10, 2012 8:40 am

And still no spark this last time that it wouldn't start? You changed the dizzy sensor and coil driver, but the stock ECM is still in control of spark, right? That, and all the wiring from the dizzy through the ECM and on to the coil driver has to be checked out. And new sensors or coil drivers can be bad... You could probably connect the MS tachin directly to the dizzy sensor, getting the MS to see rpm and operate fuel; but what's the point? It isn't going to run without spark. What about abandoning the stock ECM for spark and letting MS do that as well?
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Re: injectors over heating?

Postby yellowlt1ta » Fri Aug 10, 2012 9:25 am

thats right still no spark. stock ecu still controls spark. I also checked the voltages on the distributor and coil driver and it all checked out fine (when it was running). Im thinking about letting the MS control timing but I still dont feel confident enough to tune spark tables and set all the otherveriables that goes with it.

maybe the stock ecu just broke... idk
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Re: injectors over heating?

Postby billr » Fri Aug 10, 2012 11:41 am

There should be a lot of sources for an LT1 ignition curve; if not here then on the many, many forums, books, and articles pertaining to the SB Chevy engine. Is that all that is keeping you with the stock ECM? If so, then abandon it for the MS spark control.
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Re: injectors over heating?

Postby yellowlt1ta » Fri Aug 10, 2012 5:40 pm

that and keeping A/C. I will be making the leap to controling ignition. thank you for all your help
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