I have 3 codes in system. 18 37 73 The rpm tach needle bounces at higher rpms and will surge the engine under a load. occasionally the shift point affected. Check eng lite will come on and fade out at lower speeds. Had ignition control module tested and is good. Replaced TPS sensor and cleaned contacts on spout connector. No difference on performance. MPG varies but not dramatic. Seems to run hotter on Highway after extended driving. Am stumped?!! Please help!!!!
Keywords:Ranger
Ford CODE 18: IDM circuit failure or SPOUT circuit grounded
The computer sends out a timing advance correction to the ICM over the SPOUT wire and then looks for the change on the IDM wire.
IDM – Ignition Diagnostic Monitor
SPOUT – Spark Output Signal from EEC/PCM
ICM – Ignition Control Module
You might check the ECT or the IAT sensor for your problem.
Also check the SPOUT/IDM wire going to ground.
ECT – Engine Coolant Temperature sensor and it has two wires on it.
IAT – Intake Air Temp
IDM (feedback) is a Dark Green with a Yellow stripe wire on the distributor connector.
IDM is pin 4 on the 60 pin ECM connector.
Ok I just purchased the IAT sensor and put on vehicle. Did not stop chk eng lite. The RPM needle after truck warms will start to bounce erratically and the lite will start to illuminate and fade as well. Does the RPM gauge inside the cab work off a cable to trans? Or the Crankshaft position sensor? Or??? The surging happens under load with minimal acceleration. All problems are happening after warmed and RPM gauge starts its BOUNCE and will show at least a 1000rpm difference at times. Will show erratic reading at all speeds once starts until cooled. Any further advice appreciated. Thnx!
I am starting to think a vacuum leak may be present and the IAC is trying to compensate causing the rpms to go up and down. Check for a leak, one more thing we can rule out or hopefully correct the issue.
ok WOW!!! I really thought when you said vacuum that this guys nuts! Haha on me!!!! After inspection of entire vacuum on top of engine, I found that the 7/32 hose on charcoal canister was intact but cracky and pliable. So found a temp piece drove approx. 20 miles thru back country roads with hills and reached speeds comparable to highway and only flickered once. When reached town purchased the hose and Voila!!! Never did any rpm bounce or lite or surge!!! Both ways on rpm and surge. I want to thank you very much! Am a divorced father who has full custody of daughter and hate to think what would have cost me to have a $1.28 hose replaced!!!! Your site is very much appreciated!!!
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