Puzzling question
 

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

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)

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?

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.

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.

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

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.

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?

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.

Already done that too = (

That at that point I'd get a gauge on the fuel rail and test the pressure.

damnit cre! took the words outa my mouth... (deletes post and starts over)

if you have spark. have compression HAVE FUEL. but not getting spray at the injectors something with your pressure is most fouled.
Possible causes of a fuel-related no start include:

1. A dead fuel pump (could be the pump, pump relay pump fuse or a fault in the pump wiring circuit)
2. A plugged fuel filter
3. Low fuel pressure (weak pump, restricted fuel line, low voltage to the pump)
If the pump runs and generates normal pressure to the engine, but the engine still does not start, the problem may be: 1. No voltage to the fuel injectors (blown injector fuse or bad relay)
2. No pulse signal to the injectors from the PCM (no crank or cam sensor input to the PCM, or a bad driver circuit in the PCM, or a wiring harness problem)
3. A shorted fuel injector (robs voltage from the other injectors so none will operate)

try #3.
i know these are basically shots in the dark. but through this thread and your leg work tim, we eliminated some major culprits. your fuel pump starts. you have some flow. your spark is good and so is compression and timing. running a battery of tests is really the only way to do this.
http://www.aa1car.com/library/fuel_pump_diagnose.htm
The first check would be to check for voltage at the injectors when the key is turned on. No voltage?
Try unplugging the injectors one at a time and cranking the engine to see if it will start. If the engine starts when a particular injector has been unplugged, that's the shorted injector that needs to be replaced.

and find that damn Ohmmeter
if it makes you feel better I haven't been able to bleed my brakes cause my g/f is scared of the cold.. i have allot of air in the line and will prolly take a good 20 minutes of bleeding. but I only get 5 minutes at a time with her in the garage.
Oh and check the voltage at the pump also! let us know on that..
think were wideling down the problems. hopefully

What's the full story with this car? Was it parked for an extended period? Driver frequently? Any intermittent symptoms prior? Was any work done on the car recently?

I'm the second owner. I bought it in 1990 with 36k miles. It's garage kept, stone stock. All maintence has been done by me. It's not driven daily -avg 8k a year. Only recent work was an oil change the first of Dec. Last major service was first head gasket & 3rd timing belt around 180k in 2008. Car currently has 197k. Paint still shiny except on bumber covers & mirrors, cloth interior still looks new, some minor wear on the leather trim pieces, wheel, shifter armrest/console cover. Everything works well ('cept the lack of starting for the last 3 days) even the struts on the hood & hatch hold proudly. No leaks squeaks or rattles, everything tight & right.

Hope that helps as far as story & condition of the car. I probably need to replace the tires, good tread but starting to crack on the carcass from age. Toyo Proxies from around '03 or 04.

Okay... thanks. I don't think the dull paint on the bumper would keep it from running, but I suppose it's worth looking into. ;)

Shouldn't be getting spark from all wires and you should have at least one code if the timing belt were broken, but you can look in the oil fill hole while someone cranks it over and see if the intake cam's #1 or #2 lobe moves.

Green & Cre,

Want to thank you for your assist & input so far. I got up late and went to lunch with the wife (killed my morning). Plus I'm kinda draggin' today (over did it - old man thing), so I'm not feeling up to bending over a car. When I start back at it in a day or two (hopefully) I'll update you guys on my progress.

Great meeting you two. Talk to you soon.

Tim

looking forward to it.

Green & Cre,

I promised you two I'd give an update when felt spiffy enough to work on my supra again.

Update -
Ohmed all sensors, relays, resistors, coils, etc all read within spec.
Compression check all cylinders @ 151-152 lbs.
Fuel pressure & volume fine.
Last thing I did before I quit for the evening was unplug to injector top to the #5 cylinder, metered it to see if a voltage signal was hitting the injector while cranking. No signal. So something is causing the injectors not to fire. I'll try to trace that down tommorow or tuesday if I feel up to it. Already feeling stiff (old sucks!)

Check the Solenoid resistor on the driver's side tire well:
http://www.cygnusx1.net/Supra/Librar...ction=FI&P=111

It has power to the injectors. It appears the injectors are not grounding to fire

TSM says the ground (body point B) is on the intake manifold, and for the life of me It can't find it.

At this point I figure it is either a bad ground or a bad ECU not grounding to fire the injectors.

If one ground is bad, it may just be a better option to get a ground out diagram and clean all of the grounding points with a bristle brush or something.

My son brought over a TPS sensor he picked up from the local pull-a-part for 2 bucks. He put it on & it started right up. Go figure. (scratches head).

Thus is the way of electronics, good to hear you got it going! Now time for the fun part of owning a car... actually working on my car is fun sometimes... lol

Thanks!

I enjoyed it much more when I was a tad younger ; ) .

I'm with you on the head scratching... nothing in the TPS' circuit should interfere with the injectors.

For future reference, the ground you were looking for:
http://www.cygnusx1.net/Supra/Librar...px?S=Main&P=26