Celica No Start

Zachary Mobile Technician Austin, Texas Posted   Latest   Edited  
Discussion
Driveability
1994 Toyota Celica 1.8L (A 7A-FE)—JT2AT00N0R0023338
Crank / No Start

Hello all and thanks as always for taking the time to read and contribute. A good friend of mine owns this car and experienced the crank no start when trying to leave work yesterday evening. Initial checks revealed no spark or injector pulse. Scanner was able to communicate and see data stream but couldn't pull codes that way. Decided to skip pulling flash codes as I didn't expect much help in that department anyway seeing as it's an OBDI vehicle. 

Igniter isn't pulsing the negative side of the coil (both internal to distributor) but power feed is there. Checked for the 0-5V IGT signal at the distributor and found nothing. Scoped the cam and crank pick ups in the distributor and initially didn't see anything. Unplugged the distributor and got the waveforms you see in the first capture but noticed the crank (Red Trace) was only switching in a negative range. 

It dawned on me that the battery charger I had hooked up to the car could be interfering with these pm sensors so I unplugged it and checked again. That's when I got the second capture you see which is with the pickups plugged in. Cam & Crank trace colors are reversed here as I'd already unhooked everything by the time I thought about the battery charger. 

Unplugged the distributor & I got the same result as what's in the first capture as seen in the third picture. Again, wire colors are reversed. As a final check I made sure that crank pick up wires weren't shorted to each other or to ground. 

Rechecked the signal at the ecm with connector unplugged and plugged in and got these captures. Now not only am I getting the crank signal with the connector plugged in but it's shifted up on the scale to be more of a positive and negative switch. 

diag​.​net/file/f3g4cdz7a…

diag​.​net/file/f3lfllavv…

Still no IGT signal out of the ECM. IGT wire isn't shorted to power or ground that I can find. My assumption at this point is a failed transistor inside the ECM. ECM isn't totally dead as it did give me data stream, the check engine light stays lit cranking, and 5V ref was good when checked at the MAP sensor. The two powers (Pink wire Terminal #1 of 22 pin connector & Blk/Yel wire Terminal #12 of 22 pin connector) & 3 Grounds (2 Wht/Blk Wires Pins #13 & #26 of 26 pin connector & Brn Wire Pin #14 of 26 Pin Connector) All will light an incandescent test light that pulls approximately .2 amps. I don't have my load substitution box with me or I'd load them a bit more which I'll probably do before pulling the trigger on the ECM. Sorry for the long post, just wanted to make sure I gave you all the information I have. 

Thanks for sticking with me till the end and any input you may have. 

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Edward Owner
San Antonio, Texas
Edward Default
 

Hello Zachaey How's the IGF circuit and what color wire was IGT it's shows to be White also.

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Zachary Mobile Technician
Austin, Texas
Zachary Default
 

Hi Edward, Yes the you're write the IGT circuit is the white wire I believe pin number 20 on the 26 pin connector. Neglected to mention that. To be honest I did not check the IGF circuit because as I believe that's the feedback from the igniter to the ECM. My assumption is that there will be no feedback if the igniter isn't being triggered. I could be wrong but I thought that was the way…

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Edward Owner
San Antonio, Texas
Edward Default
 

Nope your right on about the IGF circuit ecm strategy it's a feedback but I have up loaded diagram for more input ..

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Zachary Mobile Technician
Austin, Texas
Zachary Default
 

Thank you Edward, it looks similar to what I had in my service information as well. The strategy seems to be much like Toyotas I've run into in the past where it stops sending the trigger signal if it doesn't see a feedback in four consecutive cycles. I know with the coil on plug vehicles right after this, it'll run for a second or two if it's missing one of the feedback signals and then stall…

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Darren Mechanic
West Allis, Wisconsin
Darren Default
 

Hook up scanner and check rpm data pid.

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Bob Owner/Technician
East Longmeadow, Massachusetts
Bob Default
 

Good advice. If the scanner shows RPM that means it's happy with the crank sensor. If the scanner shows RPM and there is no IGT signal, it needs an ecm. If there is no RPM seen on the scanner then the crank input circuit needs to be tested further.

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Zachary Mobile Technician
Austin, Texas
Zachary Default
 

Indeed Bob. Makes perfect sense. I don't see any drop outs in cam or crank but I'm unsure of correct phasing and amplitude. Haven't been able to locate known goods either. It also concerns me that the scaling of the crank pattern shifted from one capture to the next. I thinka little further testing will reveal the truth.

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Zachary Mobile Technician
Austin, Texas
Zachary Default
 

UPDATE Apologies to all for taking this long to follow up. Things have been crazy to say the least and I haven't been holding up my end of the Diagnostic Network bargain so to speak. After I posted this a couple weeks ago, I was able to follow up with the customer & look a little deeper. Per Darren's suggestion, I hooked up the scanner to watch the rpm data pid. Naturally the car fired…

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