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Discussion Starter · #1 ·
it idles between 1000-1600 which is definitely high.
i have replaced
IAC
MAP
CTS
egr valve solenoid
egr purge valve
egr valve gasket
throttle cable
throttle body gasket
it came up with three codes from the check engine light (OBD1)
84) exhaust gas recirculation vacuum regulator( evr circuit failure)

51) engine coolant temp sensor cts indicate -40 degrees f/ circuit open.

54) air charge temp sensor (ait) indicates -40 degrees f/ circuit open

Do OBD1 systems store codes? or do they disappear when you disconnect battery?

Also motor shakes when runs. to fix this i replaced motor and tranny mounts, tailhousing (was cracked in three pieces) (also on my truck it mounts the tranny mount) The next thing i was gonna try is replacing harmonic balancer.

Heads up this is a 1991 ford f150 with a 1994 ford f150 motor swap.
the original motor was a 302 efi. Is there a difference in computers maybe? something that needs to get plugged in the prior owner forgot? is there anything you guys recommend me to do? i would like to keep my EFI system and hear this 5.0 purr like a kitten. the spark plugs when pulled out by me and my (more mechanically inclined friend that knows more about this stuff than me) mentioned its burning good.

i have the dual catalytic system in it, could clogged catalytic converters cause anything describes above?
 

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Check your grounds first and foremost. It could be your issue with 2 different sensors with the same failure.

Also, have you verified the firing order is correct? It should be the same with both the old and new motor but just in case it was swapped.
 

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You need to sort out these codes first before getting too involved , especially these which are sending wrong info to the ECU and throwing everything out

51) engine coolant temp sensor cts indicate -40 degrees f/ circuit open.

54) air charge temp sensor (ait) indicates -40 degrees f/ circuit open
 

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Discussion Starter · #4 ·
Check your grounds first and foremost. It could be your issue with 2 different sensors with the same failure.

Also, have you verified the firing order is correct? It should be the same with both the old and new motor but just in case it was swapped.
The firing order is not the same apparently it runs on a different firing order. If I try the other firing order it won't even start. Let me see if I can find the one that works

I'll have to locate the grounds for these circuits to make sure they're good.
You need to sort out these codes first before getting too involved , especially these which are sending wrong info to the ECU and throwing everything out

51) engine coolant temp sensor cts indicate -40 degrees f/ circuit open.

54) air charge temp sensor (ait) indicates -40 degrees f/ circuit open

what do you propose? ive already replaced the things in the circuit? i will be tracing the grounds. is there anything else i can do to figure out why it would be throwing the ecu out?
 

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Discussion Starter · #5 ·
Also does anyone know where these ground locations are? im gonna try to clean up all the grounds on the truck but if i can pin point for the purpose of this issues it'd be great.
 

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Yeah the newer motor should be 1-3-7-2-6-5-4-8, but if the ecu is the stock 91 ecu then that’s part of the issue. I would verify which ecu you have in the truck first. There should be a sticker on it somewhere.
 

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it idles between 1000-1600 which is definitely high.
i have replaced
IAC
MAP
CTS
egr valve solenoid
egr purge valve
egr valve gasket
throttle cable
throttle body gasket
it came up with three codes from the check engine light (OBD1)
84) exhaust gas recirculation vacuum regulator( evr circuit failure)

51) engine coolant temp sensor cts indicate -40 degrees f/ circuit open.

54) air charge temp sensor (ait) indicates -40 degrees f/ circuit open

Do OBD1 systems store codes? or do they disappear when you disconnect battery?

Also motor shakes when runs. to fix this i replaced motor and tranny mounts, tailhousing (was cracked in three pieces) (also on my truck it mounts the tranny mount) The next thing i was gonna try is replacing harmonic balancer.

Heads up this is a 1991 ford f150 with a 1994 ford f150 motor swap.
the original motor was a 302 efi. Is there a difference in computers maybe? something that needs to get plugged in the prior owner forgot? is there anything you guys recommend me to do? i would like to keep my EFI system and hear this 5.0 purr like a kitten. the spark plugs when pulled out by me and my (more mechanically inclined friend that knows more about this stuff than me) mentioned its burning good.

i have the dual catalytic system in it, could clogged catalytic converters cause anything describes above?
I would look for a bent throttle rod or something along those lines.
 

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Discussion Starter · #8 ·
I've got the idle down to 1300 rpms while idling, the truck runs good while driving but the idle is still way too high. I am gonna start diagnosing into the codes that are being thrown at me.

Do you guys have any references for wire circuits somewhere? I would like to follow the wires and make sure everything is connected as need be.

Once I get this idle down she will run like a champ!
 

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Did you ever verify the firing order was correct? A Haynes manual or Chiltons should have the necessary wiring diagrams.
 

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Discussion Starter · #15 ·
Okay so here is where the VIN on the motor should normally be located. All I got is this but I have no luck finding this block.. could it be after market or what's going on here?
 

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There isn’t a consensus but either 94 or 95 was the first year of the 1-3-7-2-6-5-4-8 firing order. If the engine is out of a 94 with a stock cam then the issue is with the firing order. If that is not the case, then it could be a ground, vacuum leak or even the ecu.
 

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Discussion Starter · #17 ·
Getting closer I added the ait sensor and it rests at 1000 rpms but when I bring the tachometer to 2500 and drop it it goes to rest at 1500.. what are the bad symptoms of a bad egr valve? Every other thing on that egr circuit is new but that. Maybe that could affect it?
 

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Depends on the failure. If it’s stuck open it will mimmick a vacuum leak. Stuck closed and you won’t be getting very good gas mileage. How old is your map sensor?
 
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Can you get a picture or part number off the ecu? That year truck should be speed density.
 
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