92 MTX No Start code 551

[deserttiger]

Have the 92 mtx all put back together. Now crank but no start. Have spark, fuel pressure, and compression. Getting code 551 (IAC circuit). Skeptical that this would cause no start, but pulled IAC. Checked resistance - 9.5 ohms. A friend has a comprehensive online repair manual (he is a mechanic) and looked up the test. His source says the resistance should be between 50-100 ohms. Purchased new IAC. The new one reads 9.5 ohms, as well. Seriously doubt that this is out of spec, given that new and old have same reading. Any thoughts on the proper resistance ? Other ideas for cause of no start ? Any help would be appreciated. Have come a long way, having chased AC compressor all over the country, etc. Almost there, I hope !

 

[Irish Pride]

Have the 92 mtx all put back together. Now crank but no start. Have spark, fuel pressure, and compression. Getting code 551 (IAC circuit). Skeptical that this would cause no start, but pulled IAC. Checked resistance - 9.5 ohms. A friend has a comprehensive online repair manual (he is a mechanic) and looked up the test. His source says the resistance should be between 50-100 ohms. Purchased new IAC. The new one reads 9.5 ohms, as well. Seriously doubt that this is out of spec, given that new and old have same reading. Any thoughts on the proper resistance ? Other ideas for cause of no start ? Any help would be appreciated. Have come a long way, having chased AC compressor all over the country, etc. Almost there, I hope !

The IAC valve will not cause a no start condition. It will idle erratic if it's bad but the car will still start.

Furthermore, 551 is not for the IAC, it comes back as IMRC(intake manifold runner control) which should be the vacuum solenoid mounted to the back of the intake. Check to see that it is plugged in. Also, double check to make sure you have the correct pigtail going to the IAC. The pigtails for the IAC and IMRC look very similar. I don't know if it's possible that they will swap but crazier things have happened.

If the car has not been running for a while and the battery has been disconnected then the actual problem might not actually be throwing a code right now. I would double and triple check all of the harness connections and grounds.

-Chad

 

[Devin]

Trying to think of things that cause a no start. CKS definitely. SPOUT I think too. Bad grounds, especially to the intake, due to the DIS being grounded through it.

 

[deserttiger]

Trying to think of things that cause a no start. CKS definitely. SPOUT I think too. Bad grounds, especially to the intake, due to the DIS being grounded through it.

Thanks for the ideas. Interesting that the 551 code is listed as IAC in taurus/sho specific Chilton Manual. Will check grounds. Would CKS and SPOUT issues not throw codes ?

 

[deserttiger]

The IAC valve will not cause a no start condition. It will idle erratic if it's bad but the car will still start.

Furthermore, 551 is not for the IAC, it comes back as IMRC(intake manifold runner control) which should be the vacuum solenoid mounted to the back of the intake. Check to see that it is plugged in. Also, double check to make sure you have the correct pigtail going to the IAC. The pigtails for the IAC and IMRC look very similar. I don't know if it's possible that they will swap but crazier things have happened.

If the car has not been running for a while and the battery has been disconnected then the actual problem might not actually be throwing a code right now. I would double and triple check all of the harness connections and grounds.

-Chad

FWIW - both Chilton and AllData show the 551 code as IAC circuit. Further - AllData show the test being proper IAC resistance as between 50-100 ohms, as I noted above. Anyway - will check wiring, grounds, etc.

 

[BaySHO Performance]

Per Probst, the resistance should be 7-13 ohms. Alldata has it wrong. You might want to run through these other tests to see why it threw a (presumably On Demand) code.

Did you clean the fuel injectors?

 

[deserttiger]

Per Probst, the resistanc

Per Probst, the resistance should be 7-13 ohms. Alldata has it wrong. You might want to run through these other tests to see why it threw a (presumably On Demand) code.

Did you clean the fuel injectors?

View attachment 87183

e should be 7-13 ohms. Alldata has it wrong. You might want to run through these other tests to see why it threw a (presumably On Demand) code.

Did you clean the fuel injectors?

View attachment 87183

 

[deserttiger]

Thank you so much for the informative reply. Very helpful - will keep plugging away and report back. Thanks again.

 

[deserttiger]

Thank you so much for the informative reply. Very helpful - will keep plugging away and report back. Thanks again.

Replaced IAC and it fired right up. Surprised that this caused no start, but so be it. Running/Driving/Ice cold AC. Progress ! On to a few electrical gremlins - temp gauge and fuel gauge seem to be not working.