1991 FJ80 (3FE) loses power when hitting bump. Help!

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Apr 3, 2021
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British Columbia
Hello everyone I am really hoping you can help me find what this weird problem I'm having is.

When I'm driving on rough terrain and drive over something rough or even hit a pothole sometimes my RPMometer drops for a split second and my engine light (which is on cause o2 sensor I have to replace) turns off very briefly. The stereo and all other electronics do not flicker at all but I can feel the vehicle lurch as if it loses power for a second. I'm new to this vehicle and don't want this to leave me stranded out in the bush. What could this be?! Thanks for any help.
 
First thing I would to is check the battery connections to make sure they are tight and also replace the fusible links that come off the positive post of the battery. They are relatively cheap but are maintenance item often ignored. If you search this forum for "fusible links" you will find pictures. Also make sure the battery itself is secure.
 
First thing I would to is check the battery connections to make sure they are tight and also replace the fusible links that come off the positive post of the battery. They are relatively cheap but are maintenance item often ignored. If you search this forum for "fusible links" you will find pictures.
Ah I definitely should have mentioned I did replace the fusible links and the battery is brand new and connections are tight.
 
Definitely sounds like an electrical problem. Inspect all the wiring harnesses, connectors etc. Could be a failing Circuit Opening Relay or similar.
 
With the engine running, do a bit of percussive diagnostics.
The fusebox on the left fender contains the EFI relay and EFI main fuse. If there's a poor connection in either one of these, it will momentarily cut the engine.
The air flow meter just after the air cleaner has a connector that can come loose if someone has lost the thin spring clip that holds it in place. This will shut down the fuel pump.
DO NOT REMOVE THE 2 PHILLIPS SCREWS ON THE AIR FLOW METER.
 
Sounds like an intermittent short or a ground problem. Don't overlook the wires on the back of the alternator and where they route to the battery. If they short out there, it will drop voltage and the ECU will quit for a split second when voltage goes below 10 volts give or take.

If you've got fuel injector wires that have lost their insulation, a bump can cause them to short out and interrupt the injector driver signal. Start with the stuff that is easy to look over first. Had the same problem with another car once. The insulation had fallen off wires inside a loom and when they crossed, the computer freaked out. Only happened on certain types of bumps.
 

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