Puzzling question

[TonkaTim]

Hoping one of you guys will be able to help this tired old man.

I've got a stock 1987 Mk3 turbo 5-sp, it'll crank but not start. I've done all the basic checks, fuel pump flows well, good spark, all the intake hoses & tubing are solid. The puzzling part is... it's coding a 51 and I can not find any info on a 51 code. Was hoping one of you could give me a heads up.

Thanks in advance,
Tim

[Green7mgte]

Originally Posted by TonkaTim

it's coding a 51 and I can not find any info on a 51 code. Was hoping one of you could give me a heads up.
Thanks in advance,
Tim

http://www.cygnusx1.net/supra/TechTi...ror_codes.aspx
(for a 91 model, but still might be of use)

51 Switch Signal Diagnosis

• No "IDL" signal, "NSW" signal or "A/C" signal to ECU, during diagnosis check.

Trouble Area

• A/C switch circuit
• A/C switch
• A/C amplifier
• Throttle position sensor circuit
• Throttle position sensor
• ECU

[TonkaTim]

Originally Posted by Green7mgte

http://www.cygnusx1.net/supra/TechTi...ror_codes.aspx
(for a 91 model, but still might be of use)


51 Switch Signal Diagnosis

• No "IDL" signal, "NSW" signal or "A/C" signal to ECU, during diagnosis check.

Trouble Area

• A/C switch circuit
• A/C switch
• A/C amplifier
• Throttle position sensor circuit
• Throttle position sensor
• ECU

Green,

Thanks for the quick reply. I was on that site and missed that page. Was looking at the codes here http://www.cygnusx1.net/Supra/Librar...aspx?S=FI&P=28 .

Sun is starting to drop so it'll be getting cold & dark fairly soon for me. So I need to go find my ohm meter and check the reading on the TPS tommorow.

I take it no idle signal on the TPS may prevent the computer from letting the car start? (never had a TPS problem on any car I've owned)

[cre]

A code 51 will present if the TPS is not properly adjusted when the throttle is fully closed or if the TPS is unplugged... or if you press the throttle while checking error codes.

If the A/C is turned on or active this code will present or if the A/C was removed and the signal line was grounded.

NSW is not applicable.

It's academic anyway, a code 51 will not prevent the vehicle from starting and really only affects the vehicle at idle.

Have you checked the EFI relay and the EFI fuse?

[Green7mgte]

Originally Posted by TonkaTim

it'll crank but not start. I've done all the basic checks, fuel pump flows well, good spark, all the intake hoses & tubing are solid.
Tim

Found this about EFI relays. looks informative
http://www.tegger.com/hondafaq/mainr...ion/index.html


the first step is to determine if it’s a spark, fuel, or compression problem. Here’s a quick way to find out which of the three is missing. Remove a plug wire, insert a Phillips screwdriver or spare plug piece of bare wire into the plug wire boot and place the end near the engine block (do not hold the plug wire while cranking the engine unless you want a shocking experience). If there’s a spark when the engine is cranked, it has ignition. The problem is either fuel or compression. If the engine has an overhead cam with a timing belt, loosen the cover over the timing belt and check the belt


An engine that has fuel and spark, no serious vacuum leaks and cranks normally should start. The problem is compression . If it is an overhead cam engine with a rubber timing belt, a broken timing belt would be the most likely cause especially if the engine has a lot of miles on it.

looking forward to your post.

[TonkaTim]

Cre & Green,

Thanks again for the replies.


Cre - all fuses are are good. Main EFI & Fuel Pump relays are making an audible click when keyed on. Can't find my Ohm/voltage meter atm. *grumbles about sons & grandsons and missing tools*

Green - Checked the spark on all 6 plugs earlier. Should have done a compression check while I had the plugs out, but assume it is fine(new gasket in 2008). I'll do that as a precaution tommorow when I have light & its not so cold ; ). New timing belt as well in 2008. I unscrewed the oil cap and watched the cam turn so belt is good as well.

I'm only hearing 1 click on the EFI relay so maybe it is not powering the injectors I'll check that tommorow as well. Maybe some kind of fuel cut problem. When I pulled the plugs they & the tops of the pistons were dry , no fuel smell. When I jumper the fuel pump it FLOWS, so no pump problems. Thought maybe the 51 code might be affecting the fuel circuit.

Again all help is appreciated, I have a very basic understanding of EFI, but definately no expert.

[Green7mgte]

Originally Posted by TonkaTim

Cre & Green,
*grumbles about sons & grandsons and missing tools*

Hah! that one takes me back, always loosing my gramps tools also. Guess it wasent just me!

well damn. that eliminates spark, fuel, and compression..
how about proper timing ( the engine valves should open and close in appropriate time.)
Thats all of my "simple" ideas. gonna have to go back and re evaluate other issues instead of throwing out more ideas and moving off track.
Problem with engine electronics. crank sensor, cam sensor, air flow sensor, power relay, engine computer
Ignition system problems ignition coil, commutator,distributor cap, etc.
let us know on the injectors. good luck, oh and stay warm.
The timing idea is just something outa left field I wouldent even waste time with it. but could be a possibility. I would do the electrical tests again before moving into "left field" so to speak.

the 1 click sound is the clue were looking for perhaps? Run your hand across the relay and see if you can "feel" the clicks. Cause i only hear one also. hah

oh and for the compression check just to eliminate it, the car wont start if below 70-80 psi.

read this too for electric troubleshooting. http://www.nls.net/mp/volks/htm/spark.htm

[cre]

Agreed, I would start with checking the electrical first... Specifically, I would pull a spark plug wire and check for spark while someone is cranking the ignition.

[TonkaTim]

I can only feel & hear one click on the EFI relay.


I checked all 6 plugs by block grounding them & cranking over. All fired. That should mean I'm good on fire through the whole system. If it was a timing issue it would sputter spark the fuel.

It seems something is cutting the fuel circuit, only thing I can assume, especially when I pulled the plugs after several cranking attempts & the plugs were dry(no fuel in combustion chambers). If I can't find my meter I may have to buy another one = ( and start chasing circuits. I was reading over the schematics on the cygnusx1 site seems the fuel circuit runs through the AFM as well. May be just a bad ground somewhere. Unless the TPS with no IDL signal cuts fuel at the ECU.

Favor? - If either of you have a chance mind unplugging your TPS & see if it cranks?

[cre]

Cranks fine without the TPS, trust me... the car is even drivable with out the TPS... just rough.

Tyr placing a jumper across FP and B+ in the diagnostic box in the engine bay and then try to start. This bypasses a couple relays and powers the fuel pump directly... it'll help eliminate a bad pump as a possibility.