All sensors unplugged and the truck still runs.

[Sardust]

Hey everybody iv got an 86 ranger that I stuck an efi 302 from an 88 f150 into. The trucks been running and driving fine for about a week. Yesterday I was driving and as I was shifting from second to third I noticed the idle stayed up. Got to the next red light and reved it up it did not go down. I cleaned the iac and sprayed the cleaner through the intake. No change. I unhooked the battery for the day hooked it up after work to clear the computer. Still idles high and runs rough a bit. Hooked up a vacuum tester and it's a steady 20. I started pulling plugs from sensors and not one of them made any difference. I unplugged all the sensors at the same time it kept running. I shut it off and restarted it with all unplugged. Any ideas or suggestions?

 

[RonD]

Well the sensors don't make the engine run, they just report data to the computer.
The computer has basic pre-loaded info it uses when sensors fail, or are unplugged, lol.
It will be sluggish but usually drivable, this is called "limp home mode"

Your CEL(check engine light) should have come on with sensors unplugged, if not then I would suspect a computer issue.

The '88 engine should have TFI system for spark and RPM, the computer uses this RPM reading to set idle with the IAC valve.
TFI systems are pretty old now and have 100% failure rate at this point in time, so it could be a TFI issue.

Good read here on TFI: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

 

[Sardust]

Could my o2 sensor not being installed cause all of this? I just saw the plug hasn't been in the whole time iv been driving the truck. I guess I forgot to hook it up.

 

[RonD]

No, but CEL should have been on....................
And if it runs poorly cold and warm then for sure not O2 sensor related, O2 sensors can not be used until they are above 600degF, so computer ignores O2 data for at least 4 or 5 minutes after a cold start.

If you have hooked up BOTH upstream O2 sensors then unhook the battery for 5 minutes to reset computer.

 

[Sardust]

I'll do that and try another computer I have then move to the module on the distributor. I think I probably overheated the computer as I hadn't moved it to inside the cab yet ... I'll post when I find the culprit. Thanks for your help!!

 

[Sardust]

I learnt that driving with your computer in the engine compartment for even a small amount of time is catastrophic. Put in a used EEC and it's running good again.

 

[RonD]

Good work

Thanks for the update