code 51/ quits when returning to idle - Page 3

cre · 01-30-2012, 03:53 AM

32 is a short in the HAC circuit, not related to the turbo. I don't recall you Mentioning this previously. It's not shown in the 89+ TEWD because in the later model ECUs (mid89 and later) the HAC sensor was incorporated into the ECU itself. In early '89 and prior it was an external sensor mounted behind the glove box near the hinge... three wires. I think it too gets it's power from Vc as well as does the AFM... if so there's a very likely tie in. I believe both also use E2 as ground. Have you tested Vc? A short in the wiring harness or a bad ECU would account for all three related problems.

With regard to the TPS, I forgot to mention that automatic transmissions do rely on it more than manuals... in this case driving with it unplugged or damaged will probably result in even worse performance.... Which do you have?

Analog meters refresh more slowly so signals with oscillations are essentially averaged out. Reading Vf with a digital meter, for example, may show a bouncing signal which never stabilizes (say from 2.5 to 5V, back and forth and numbers in between).... with an analog meter it'll show 3.75 with only a slight flutter to the needle. Some DMMs do have a function to mimic this behavior.

The stock boost gauge is not a diagnostic tool by any means and I recommend you not expect anything more from it then you would from a 'dummy light'. The engine operates just like an N/A engine until the compressor starts spooling up; In vacuum. Until the compressor is spooling and producing enough compression to raise the manifold absolute pressure to ambient the engine remains in vacuum and any good boost gauge will reflect this.

You can test the KVAFM.... with Toyota's publication on advanced diagnostics and repair (this also covers ECU's, IIRC), a flow bench and an oscilloscope. I suppose you could test one with a leaf blower, an oscilloscope, a known good KVAFM (as reference) and the suspect KVAFM connected in series....

Yes, it's normal for the vent mode to remain lit as ling as the button is pressed. As long as the A/C switch is off (and it's LED, naturally) you're fine and barring a wiring issue the code 51 would only be caused by the TPS or a bad ECU.

Limp mode is only entered when a condition exists that the ECU believes is critical to an extreme degree. It doesn't even go into limp mode for a 'lean condition detected' error code, if memory serves correctly. Issues such as severe knock, damage to the ECU or malfunction of critical electronic components (there aren't many of there actually); I believe on the 7M-GTE an oil pressure signal of 0 at the ECU or at least a fluctuating oil pressure signal may cause it as well.... does your factory oil pressure gauge work?

cre · 01-30-2012, 03:57 AM

Here you go:

http://www.supra.co.nz/87tsrm/EFI/efi121.htm

EDIT:
1987 TRSM: http://www.supra.co.nz/87tsrm/index.htm

professorbob · 01-31-2012, 07:02 PM

Thanks for the Link, I will check out the HAC High Altitude Control values.
After extensive reading at this site www.autoship101.com I learned there is a relation with the brake light switch and the engine control.
I have a panel light that indicates there is a problem with the brake lights.
Just wondering if you know which fuse controls the brake light circuit so I can remove it.
Am thinking that the ECU may be affecting the fuel cutoff because it thinks that the brakes are being applied.

I plan on purchasing a replacement Throttle position sensor as well because of the fact that it is out of spec. I am hoping this will also improve the starting on first try rather than the present 4- tries.
Thanks for you help.
Robert

cre · 01-31-2012, 09:04 PM

The brake fuel trim is VERY minimal and is reliant on other sensor data from what I recall.... Otherwise, brake-boosting would be impossible in these cars but it's actually VERY easy.

Do keep in mind that those publications cover MANY years and many years of changes and evolution. A lot of it has no relevance with regard to TCCS and earlier systems.

gtgassman · 10-06-2016, 12:21 PM

Hi guys new to this forum, any update on this my son and I have been restoring a 1989. We had the head straightened and machined and a valve job done on it, reassembled the motor and are having the same issues that professerbob was having. Won't rev over 2500. changed the MAF and the TPS no vac leaks and no codes. I am going to check the grounds, but any other thoughts would be appreciated. My son is an eleventh grader in automotive tech and this has the teacher confused. Thanks

01-30-2012, 03:53 AM	#21
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	32 is a short in the HAC circuit, not related to the turbo. I don't recall you Mentioning this previously. It's not shown in the 89+ TEWD because in the later model ECUs (mid89 and later) the HAC sensor was incorporated into the ECU itself. In early '89 and prior it was an external sensor mounted behind the glove box near the hinge... three wires. I think it too gets it's power from Vc as well as does the AFM... if so there's a very likely tie in. I believe both also use E2 as ground. Have you tested Vc? A short in the wiring harness or a bad ECU would account for all three related problems. With regard to the TPS, I forgot to mention that automatic transmissions do rely on it more than manuals... in this case driving with it unplugged or damaged will probably result in even worse performance.... Which do you have? Analog meters refresh more slowly so signals with oscillations are essentially averaged out. Reading Vf with a digital meter, for example, may show a bouncing signal which never stabilizes (say from 2.5 to 5V, back and forth and numbers in between).... with an analog meter it'll show 3.75 with only a slight flutter to the needle. Some DMMs do have a function to mimic this behavior. The stock boost gauge is not a diagnostic tool by any means and I recommend you not expect anything more from it then you would from a 'dummy light'. The engine operates just like an N/A engine until the compressor starts spooling up; In vacuum. Until the compressor is spooling and producing enough compression to raise the manifold absolute pressure to ambient the engine remains in vacuum and any good boost gauge will reflect this. You can test the KVAFM.... with Toyota's publication on advanced diagnostics and repair (this also covers ECU's, IIRC), a flow bench and an oscilloscope. I suppose you could test one with a leaf blower, an oscilloscope, a known good KVAFM (as reference) and the suspect KVAFM connected in series.... Yes, it's normal for the vent mode to remain lit as ling as the button is pressed. As long as the A/C switch is off (and it's LED, naturally) you're fine and barring a wiring issue the code 51 would only be caused by the TPS or a bad ECU. Limp mode is only entered when a condition exists that the ECU believes is critical to an extreme degree. It doesn't even go into limp mode for a 'lean condition detected' error code, if memory serves correctly. Issues such as severe knock, damage to the ECU or malfunction of critical electronic components (there aren't many of there actually); I believe on the 7M-GTE an oil pressure signal of 0 at the ECU or at least a fluctuating oil pressure signal may cause it as well.... does your factory oil pressure gauge work? __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

01-30-2012, 03:57 AM	#22
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	Here you go: http://www.supra.co.nz/87tsrm/EFI/efi121.htm EDIT: 1987 TRSM: http://www.supra.co.nz/87tsrm/index.htm __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

01-31-2012, 07:02 PM	#23
professorbob Intake Join Date: Nov 2007 Location: Lavonia Posts: 49	Engine Stopping update Thanks for the Link, I will check out the HAC High Altitude Control values. After extensive reading at this site www.autoship101.com I learned there is a relation with the brake light switch and the engine control. I have a panel light that indicates there is a problem with the brake lights. Just wondering if you know which fuse controls the brake light circuit so I can remove it. Am thinking that the ECU may be affecting the fuel cutoff because it thinks that the brakes are being applied. I plan on purchasing a replacement Throttle position sensor as well because of the fact that it is out of spec. I am hoping this will also improve the starting on first try rather than the present 4- tries. Thanks for you help. Robert

01-31-2012, 09:04 PM	#24
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	The brake fuel trim is VERY minimal and is reliant on other sensor data from what I recall.... Otherwise, brake-boosting would be impossible in these cars but it's actually VERY easy. Do keep in mind that those publications cover MANY years and many years of changes and evolution. A lot of it has no relevance with regard to TCCS and earlier systems. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

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10-06-2016, 12:21 PM	#25
gtgassman Stock Join Date: Oct 2016 Location: Ct Posts: 1	Hi guys new to this forum, any update on this my son and I have been restoring a 1989. We had the head straightened and machined and a valve job done on it, reassembled the motor and are having the same issues that professerbob was having. Won't rev over 2500. changed the MAF and the TPS no vac leaks and no codes. I am going to check the grounds, but any other thoughts would be appreciated. My son is an eleventh grader in automotive tech and this has the teacher confused. Thanks