I recently purchased my 88 turbo supra. After correcting the vacuum leaks and rigged up mess the prior owner did, the car won't start. It cranks over fine even though it backfires a bit. It now shows a code 51. I'm affraid that it's going to be a bad ecu. Can a bad or misadjusted tps cause the engine to not start? I'm going to adjust the tps today and try to start it again, but could this be the ecu? Any tips and prior experiences would be greatly appreciated. Thanks.
Code 51(TPS or ECU)
- Thread starter fastazzsupra
- Start date
it's almost never the ECU. try unplugging the TPS and starting the car. if it starts, it should idle around 1k rpm with no connection to the TPS. 
also, if it starts, that also tells you where your problem is
-shaeff
also, if it starts, that also tells you where your problem is
-shaeff
Use the TSRM to adjust the TPS. If that doesn't work, replace it. I had this problem recently and an adjustment fixed it right up.
The TPS will not cause your car to not start, no matter how messed up it is.
And if the ECU is smart enough to give you error codes, the chances of it being bad are almost nil. The ECU never seems to goes bad anyway, it's all the fried wires from the sensors that cause the problems.
And if the ECU is smart enough to give you error codes, the chances of it being bad are almost nil. The ECU never seems to goes bad anyway, it's all the fried wires from the sensors that cause the problems.
I tested the tps today and found out it was bad and out of adjustment. I adjusted it and then tested it by the online manuals. The sensor was reading the same at open as closed. This would probably be the cause of the backfires and my fuel soaked plugs. What else would cause a code 51 besides what the manuals say? Ecu plugs had a little dirt or something in them, but are now clean, but I think the ecu is working fine, thank god. Anyone else have an opinion or tip to share? Thanks for the info and help so far guys. This is the best supra forum yet. Thanks.
Is anyone still here? Has anyone had this problem yet or do I have a lemon to get rid of? I really need some advice guys. Thanks.
We need more information...
Did it start before?
Are you sure all of the vacuum leaks are fixed?
Does it run AT ALL? (does it just run roughly w/backfiring?)
What was the mess that you corrected?
Did it start before?
Are you sure all of the vacuum leaks are fixed?
Does it run AT ALL? (does it just run roughly w/backfiring?)
What was the mess that you corrected?
Did you search the forum? This has been covered many times. How did you test the TPS? What did you find "bad" about it? If it was bad why didn't you replace it? Shawndude and Shaeff are right, the car should still start without the TPS connected..
The TPS has two distinct portions: 1) a potentiometer that measures throttle plate angle and 2) a set of contacts that close when the throttle plate is fully closed (IDL contact). The reason you set the TPS as per the manual is to both calibrate the throttle angle to the TPS and to calibrate the idle contacts.
The IDL contacts control various functions, the main ones being to tell the ECU to cut injection during rapid deceleration (to reduce HC emissions) and to enable the idle speed control (ISC) system. The pot in the TPS fuctions in the same mammer as the accelerator pump in a carb. It tells the ECU the *rate* of throttle opening. It's also is used to tell the ECU when to go into flooded start mode. This is why you should never hold the pedal to the floor when cranking. Lord knows why you'd do that in other than a flooded start but just so you're aware of it.
Code 51 is caused by the IDL contacts not being closed when the throttle is closed. Jumper the diag block and turn the key on. You should get a normal code. If you press the gas pedal slighty code 51 should appear and then disappear as you release the pedal. This is a quick way to test the IDL contacts if you're too lazy to ohm them out at the TPS.
Code 51 is also used to test the wiring in the AC system. When used this way it's only a diagnostic and will not effect how the car runs. 99% of code 51s are caused by anything that results in the IDL contacts being opened ie; bad wiring or a misadjusted TPS. Do as I said and check it with the engine off and E1 and T shorted. If you get a code 51 all the time then either measure the IDL contact on the TPS to see if it's closed or short the IDL pins in the TPS harness. One or the other will point you to either a bad TPS or bad wiring.
The TPS has two distinct portions: 1) a potentiometer that measures throttle plate angle and 2) a set of contacts that close when the throttle plate is fully closed (IDL contact). The reason you set the TPS as per the manual is to both calibrate the throttle angle to the TPS and to calibrate the idle contacts.
The IDL contacts control various functions, the main ones being to tell the ECU to cut injection during rapid deceleration (to reduce HC emissions) and to enable the idle speed control (ISC) system. The pot in the TPS fuctions in the same mammer as the accelerator pump in a carb. It tells the ECU the *rate* of throttle opening. It's also is used to tell the ECU when to go into flooded start mode. This is why you should never hold the pedal to the floor when cranking. Lord knows why you'd do that in other than a flooded start but just so you're aware of it.
Code 51 is caused by the IDL contacts not being closed when the throttle is closed. Jumper the diag block and turn the key on. You should get a normal code. If you press the gas pedal slighty code 51 should appear and then disappear as you release the pedal. This is a quick way to test the IDL contacts if you're too lazy to ohm them out at the TPS.
Code 51 is also used to test the wiring in the AC system. When used this way it's only a diagnostic and will not effect how the car runs. 99% of code 51s are caused by anything that results in the IDL contacts being opened ie; bad wiring or a misadjusted TPS. Do as I said and check it with the engine off and E1 and T shorted. If you get a code 51 all the time then either measure the IDL contact on the TPS to see if it's closed or short the IDL pins in the TPS harness. One or the other will point you to either a bad TPS or bad wiring.
The way I now the tps is bad is because with it off the car the sensor resistance was out of spec, even after adjusting it. The mess I refered to was the vacuum routing screwed up, the knock sensor harnesses cut off, and absolutely no emissions system parts at all. The car ran when I bought it a month ago, but at idle it would stall without some gas thrown at it. The only code in the ecu is the code 51. If the tps isn't the culprit, what can be? Before this I had a code 22. The ignition harness coils to igniter was bad and replaced. The tps was ordered two days ago and will be here tomorrow. I appreciated all the advice ya'll have given me so far, but I suck at electrical diagnostics. The tps was showing the same reading at closed and at open. So how I see it the tps is telling the ecu that there is full throttle, but it is closed. That explained the plugs being drenched with fuel and the backfires. I had the fuel pressure vsv unplgged, would that help it start? I'm just getting into toyotas, so I need all the help I can get for now. Do I jump the E1/T while cranking and look for the codes then? Or do I just keep checking after I crank it over? Thanks.