Engine shuts off on highway

[Maciasmarci]

I have 1990 5.0 306 with gt40 heads/upper and lower intake , 70mm throttle body, b-cam , smog delete, h-pipe , and welded diff. Around 70 mph either on 4th or 5th the engine just dies while accelerating or decelerating. Any idea? I re adjusted my tps several times. I only drive this in the streets most of the time.

 

[AeroCoupe]

Does the engine just die but all the electrical stays functioning?

 

[Maciasmarci]

Yes all the lights stay on, engine doesn’t even shake or stumble it just dies .

 

[AeroCoupe]

Have you pulled codes? Remember the CEL does not have to come on for there to be codes.

 

[Maciasmarci]

No not yet

 

[AeroCoupe]

Pull them and post back.

 

[Mustang5L5]

Does it die at any other conditions? Only while cruising?

Does it fire back up if you kick the clutch in?

 

[Maciasmarci]

Only dies when I’m on the highway on 4th or 5th gear about 70 mph and all I do is throw it in neutral and turn the engine back on. It never dies when I’m cruising I’n the city.

 

[Maciasmarci]

Codes I pulled up while engine cold..
KOEO - 54,31,85,18,22,29,96
KOER- 98,54

 

[Mustang5L5]

Codes I pulled up while engine cold..
KOEO - 54,31,85,18,22,29,96
KOER- 98,54

Not an insignificant amount of codes. How well does the car run? Some of these are big codes?

Code 54 - ACT sensor out of range
Code 31- EGR EVP below min range
Code 85- Canister purge inoperative
Code 18 - Spout out or wiring fault. (this one might be your issue) See this thread https://stangnet.com/mustang-forums/threads/help-code-18.896093/#post-9031071

Code 22 - MAP out of range
Code 29 - VSS not reading
Code 96 - Fuel pump secondary circuit failure
Code 98 - Did not pass KOEO test. Hard faults present

You need to fix that code 18 before you can proceed to KOER tests, but the code 54, 22, 29 and 96 need to also be addressed.

Is the EGR and charcoal canister deleted?


NO TPS codes, which means it's in the proper range. No need to adjust it any further.


Any chance those are old codes? You might want to erase the codes, and then go for a 10 min drive and a few key cycles and then pull them again.

 

[Maciasmarci]

I’ve checked continuity on my front harness to my ecu a while back and everything checked out fine but you never really know. I’ll check again. But can the engine shut off on acceleration due to a lean/rich mixture?

 

[Maciasmarci]

Yes the canister and egr were deleted but it doesn’t have the dummy plug on the connector to bypass it.

 

[GTFIVE.O]

I had this happen to me once. Have you checked all your spark plug wires ? That was my issue I had a bad one .

 

[Mindseye007]

I have 1990 5.0 306 with gt40 heads/upper and lower intake , 70mm throttle body, b-cam , smog delete, h-pipe , and welded diff. Around 70 mph either on 4th or 5th the engine just dies while accelerating or decelerating. Any idea? I re adjusted my tps several times. I only drive this in the streets most of the time.

Does the RPM gauge jump around? While crusing ? Code 18 I bet your TFI Module is starting to short out and might be on its last legs before the stang completely shuts off I would change that first thing. Then see how it runs and do the KOER TEST again.

 

[Rcdgl]

My 79 did this because the ignition switch on the column got out of adjustment, apparently the motion of the keys in the cylinder caused it to move out of the on position....

 

[Mindseye007]

My 79 did this because the ignition switch on the column got out of adjustment, apparently the motion of the keys in the cylinder caused it to move out of the on position....

Here you go get it here https://lmr.com/item/LRS-11582AR/79-93-Mustang-Ignition-Cylinder-With-Key-Chrome-Reproduction there is a brief install video, scroll down on the LMR Page.