1996 Crusader 7.4l XLi Idle and Running Issues

Hello, I'm new to the Crusader forum and was hoping for a little help. I just had a top end job done and a few issues have surfaced that were not there before. I have a High Temp idiot light that won't go out even after new sensor, the engine will not settle below 900rpms, and if I rev to 2,000 RPMs, the alarm tones and the RPMs drop to idle. At key on, I get a solid tone for 2 seconds. Sometimes when I fire the engine the high temp idiot light doesn't come on and others it does. It always won't go past 2,000 RPMs though. I checked the vacuum line and it's good, what does it plug in to under the breaker cover? I'm pulling my hair out.

Lights are typically controlled by a switch (vs a sender unit)….and it sounds like you may have multiple issues and I'd bet they are associated with the recent repair.

I'd suggest getting a scan tool and seeing what the ECU sees and go from there. if a scan tool isn't available, and you are handy with electronics, there are plenty of www posting on how to make a code reader for your early MEFI controller. Also, get the MEFI-1/2 manual off the www - it will give you the theory of operation along with the diagnostic procedures for any codes you find.

I have been trying to find the basic CodeMate reader to purchase and haven't found one for sale. I have seen the paperclip and LED code reader write up. I will find and download the MEFI 1/2 manual. Is there somewhere I can get the Service Manual for s/n: 097915, I found the parts manual thanks to another thread here.

I'm going to replace the MAP and run a new vacuum line, and if that doesn't work, I'm going to replace the IAC next. Would you happen to know where the high temp switch is located?

codemates used to available on the www....~ $100 last time I looked.

Crusader (PCM) sells service manuals as do most dealers.....as far as engine troubles go, whats in the Delphi MEFI manuals is adequate for probably 95% of the issues you see and will give you insight into the other 5%......and the Delphi material is almost always 'pasted' into the OEM service literature.....the benefit to the factory data is usually a clear indication of the options that were implemented on the particular models.....

As far as the switch, if it is used, you can find the pin used in the MEFI-1/2 book and then trace back the wiring harness looking for the wire color(s) on that pin. anything tied to the cooling system has a switch/sender in the water jacket of the block so there aren't that many places to look. it is possible that the ECU reads the temp SENDER and then drives the light ON if the indicated temperature exceeds a given level....it will depend upon what is used on the dash.

Finally, be aware that the mid- to late-90's was a period when a lot was changing regarding engine controls....sometimes things aren't current in the shop manuals, as printed....

Great info, thanks for the help. I looked through the parts manual and didn't see anything on a switch. I did put plumbing tape around the temp sensor, thinking back, I wonder if the metal to metal contact is grounding and the tape is interfering.

If you only used two wraps and its screwed in tight enough, you should be ok....an ohm meter will tell you for sure - its a low current circuit...

Update: Mechanic didn't make some connections and had wrong connections in the wrong places. Minus a shakedown run, I'm back in business. Thank you for the help, it's greatly appreciated!