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Code 51!! Help!!

5K views 25 replies 9 participants last post by  customd2000 
#1 ·
1991 5sfe. this is what happens, i try starting the car and it likes to sputter and backfire alot. it will only stay running when if i keep my foot in the pedal. then after a little bit of that going on it will "catch" and rev up and run normally for a while. sometimes it will run great all day and even start up great! but then other times it will want to die when i am going down the road (drop about 1000 rpm and start backfiring again). problem doesnt happen all the time which makes it hard to figure out. with the code being a 51, what could it be?? its my only vehicle so any help would be great. thanks! Oh and i also put a timing light on it and when it messed up the light stopped blinking but the engine was still trying to run....
 
#5 · (Edited)
I got a TPS for about $50 from Toyota. Keep in mind that I get a discount through my company...I believe list is about $60-65.

89452-22010 - Manual Trans

89452-12040 - Auto Trans (hopefully this is not you....list is $95)

However:

1. Loosen the two set screws that secure the TPS to the throttle housing. (DO NOT REMOVE THE SCREWS)

2. Connect an Ohmmeter to terminals IDL and E2 of the TPS after removing the connector.

3. Insert a 0.028 in. (0.70 mm) feeler gauge between the throttle stop screw and stop lever.

4. Rotate the TPS counter-clockwise and slowly back clockwise until the Ohmmeter just looses continuity, (infinite ohms).

5. Secure the TPS with the two set screws.

6. Remove the feeler gauge and recheck TPS setting.

7. There should be continuity with a 0.020 in. (0.50 mm) feeler gauge inserted in the stop. There should be NO continuity with a 0.035 in. (0.90 mm) feeler gauge inserted in the stop.

8. Remove the Ohmmeter and reconnect the TPS connector.

w/ AUTOMATIC TRANSMISSION:

1. Loosen the two set screws that secure the TPS to the throttle housing. (DO NOT REMOVE THE SCREWS)

2. Connect an Ohmmeter to terminals IDL and E2 of the TPS after removing the connector.

3. Insert a 0.024 in. (0.60 mm) feeler gauge between the throttle stop screw and stop lever.

4. Rotate the TPS counter-clockwise and slowly back clockwise until the Ohmmeter just looses continuity, (infinite ohms).

5. Secure the TPS with the two set screws.

6. Remove the feeler gauge and recheck TPS setting.

7. There should be continuity with a 0.020 in. (0.50 mm) feeler gauge inserted in the stop. There should be NO continuity with a 0.028 in. (0.70 mm) feeler gauge inserted in the stop.

8. Remove the Ohmmeter and reconnect the TPS connector.
 
#8 ·
i found a tp sensor for a little over $50 at a parts store. bad news is that i dont have a DVOM, it was stolen. And i've never messed with the tp sensor since i've had the car so i'm pretty sure its the sensor. do new tp sensors come pre-calibrated so all i would have to do is center it up and screw it on??
 
#10 ·
well i finally figured it out. it was the ignition coil!! i am happy that i know now but am pissed because the computer sent me in the wrong direction. reason it did is because the middle pin on the tp sensor goes to the ecu as a signal wire....that same wire splices off unto other parts of the engine harness into other plugs, (like the ignition coil plug) which is why the computer told me it was a short in the tp circuit. well at least thats what i think is the reason why. i plan on picking up a new one tomorrow and getting it up and running again. thanks guys....Peace!!
 
#11 ·
mr2project_5sfe said:
well i finally figured it out. it was the ignition coil!! i am happy that i know now but am pissed because the computer sent me in the wrong direction. reason it did is because the middle pin on the tp sensor goes to the ecu as a signal wire....that same wire splices off unto other parts of the engine harness into other plugs, (like the ignition coil plug) which is why the computer told me it was a short in the tp circuit. well at least thats what i think is the reason why. i plan on picking up a new one tomorrow and getting it up and running again. thanks guys....Peace!!
Ah, all the reason why OBDI was overhauled and made into OBDII. Well, hope everything works out so you can get to driving your 2 again.
 
#12 ·
Great Nick! See should have just went with me and my gut initially when I said it was your coil! ;) It had all the symptoms of the coil but the code 51 was just making us second guess! Sucks that you pulled the engine harness but it good though because it's how you finally figured out that it was the coil for sure! Told you it was something simple! :thumbup
 
#13 ·
bad news!!! its not just the ignition coil, but also the ignition control module!! :( i am really depressed right now because i have absolutely NO money!!! this sucks! and there is a grey plug that is right next to the ignition coil....what is it for?? hope its nothing important because i lost it. i hate this whole situation.
 
#15 ·
now i am really starting to wonder if it was the distributor connector, cause when i would move the distributor to advance or retard the timeing it seems to want to run more often. would the engine run the same way without it disconnected??? but this doesnt explain why i have a code 51!!! this is really starting to make me upset.
 
#20 ·
well i checked the tp sensor and i have five volts going to it so thats good. but when i would open the throttle, it would stay at five volts then cut instantly to 0 volts. isnt it supposed to slowly go down to 0 volts. like an analog signal? well, I'll get the new connector first and let you guys know if that fixes the problem.
 
#21 ·
Reviving an old thread. Interesting read...
I have similar issues on my 91 3SGTE. Did you ever resolve this?

I've chased this in a very similar process. I have a code 51, and there is some question as to whether or not it is meaningful. I do know I have a strange voltage on the TPS. I'm pretty sure it's adjusted correctly (tested it several times and on two different TPS's), and it passes all the resistance tests. When installed, the voltage on the IDL and E2 pins (on the ECU) read 0 volts until open the throttle part way. After it's open part way, the voltage goes to 11V. It remains at 11V until fully open and stays at 11V.

I looked at the wiring diagrams for the TPS, the distributor, the igniter, etc. There is nothing in those diagrams that seems to relate to the IDL signal. I do know the IDL wire is also shared with the cruise control ECU. That seems to be the only additional connection with the IDL that I can find. I'm not sure how I could have 11V on the signal, if there is no issue with the cruise control ECU (I disconnected it) and the TPS tests correctly.

I do have a degrading wiring harness. I broken the IDL wire at the TPS connector and had to solder it back together. I imagine I could have an issue with other connectors (i.e. the distributor connector), but I don't see any connection to the IDL signal with any of the rest of the components in the system.
 
#23 ·
In this entire thread, no one put up what code 51 is actually supposed to be. I have never had a 5S engine, or I would look it up myself. Maybe with some more information someone would have advice.

This doesn't happen to be the switch position code, by any chance?
 
#26 ·
I found my issue. Ok...so I removed the whole throttle body, got my feeler gauges and went to work.....2 tps later, I finally got some decent readings. Now here is where the issue was.... I checked the engine light and code was still there, even after resetting the ecu. So as I looked closer...the throttle cable was holding the needle from touching..as soon as i calibrated the cable...code went away. Still not starting but I'll mess with the dizzy timing later. No more codes whoo hooo
 
#24 ·
I am not sure... car sat for 5 years....within those 5 years we've had a couple polar vortex and hot weather in the summer. I'm almost about to give in... my next step would be the whole wire harness. I did find that when I turn on my lights....my blinkers turn on as if they are the norm lights . The plot thickens. I'm in the middle of plugging in all the connections after disassembling everything.
 
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