Crank no start, EFI relay circuit fault

Hello!

98 Tacoma base model 2wd or as my friends call it, poverty spec.

I'm not an electrical expert so bare with me.

It's cranking over strong but not starting. We rented a relay tester, when we plug it into the EFI relay socket we can get the truck to start. With a new EFI relay it will not start. The tester is indicating a fault on terminal 86 which I believe is the low current side of the relay. A multi meter shows a tiny amount of voltage on what i think is the ground side, about 0.1-0.3v.

I think it's safe to say there is a short somewhere feeding current back up the ground. I'm not sure if that's possible. We unplugged every non-essential fuse to see if we could eliminate the fault, no luck.

I'm not really sure where to start now. We're going to remove the fuse box to see if we can see a short on the backside but my confidence is low. Any suggestions would be appreciated. Thanks!

 

Not a short, an open.

You can always jump your relay trigger using the key ACC wire if you dissect your steering wheel column

 

Hi, thank you for the response.

How would an open circuit show a small voltage?

Today we got a POWER PROBE Short/Open Circuit Tester and we will try to track down the issue.

 

Sorry, I guess I misread a little. A tiny voltage on the ground side is normal and will depend where you had the other probe - ground terminal of battery? Body? Engine?
To be really sure, switch to amps mode and connect the ground pin to the ground terminal. If you really have something feeding that wire, the current will not read 0.

 

There is a post call "Circuit open relay location" and there is a wiring diagram there plus a good description of its operation.

 

Thank you treyus30, I'll give that a try.

Glamisman if I understand correctly the Circuit Open Relay is just the fuel pump relay.

 

Really need to get a test light and see what your missing on the control side of the relay, shouldn't be hard to diagnose. Could be a simple as a blown IGN fuse.

Pin 3 should be Power from the IGN Fuse (7.5A) in the interior fuse box (Hot in Run & Start)
Pin 4 should be constant Ground from Ground Point EA on the left quarter panel.

 

The best answer I can give you is "kind of". The circuit opening relay (COR) is exactly what its name describes, it opens the circuit that powers the fuel pump. When you turn the key to the crank position a signal is sent to the powertrain control module (PCM) and the circuit opening relay control side is grounded via the PCM and the fuel pump runs. When you release the key to the run position the crankshaft position sensor (CKP) sends a signal to the PCM saying hey the motor is turning over and it grounds the control side of the COR through the PCM.

In addition if you have a manual transmission there is a clutch switch that needs to be closed by pushing the clutch pedal and if it is an automatic the shifter has to be in park or neutral.

 

I just recently ran into an issue and traced it down to the COR. That thread @Glamisman posted was a big help!

Crank but no start. Was able to jumper it using the diagnostic port under the hood and it started and ran just fine. I foolishly bought a replacement relay on eBay because I think messing with the existing relay (removing it/banging/tapping/etc) may have fixed it. That may have been temporary or short lived anyway so I probably would have need to buy a replacement in the end regardless.

 

Not much to report but I wanted to keep the thread alive. I promise to let everyone know what fixes the truck.

I'm not with the truck, it's out of state, long story. So the feedback loop takes a while.

I've ordered a COR relay which should come this week. I'll check in when we get that swapped in.

 

Another update but not a good one.

A new COR relay did not fix the problem.

One thing to note is when we try to start the truck there are no codes. But when we run the relay tester, which lets us start the truck there are two codes. P1310 and P1300

 

THE TRUCK IS FIXED!!!

As promised I wouldn't leave everyone hanging, we all hate unfinished threads.

This was really hard to diagnose but the socket that holds the EFI fuse under the dash was loose. A previous owner must have jammed a wire in there to pull power for some accessory. Not a great fix but we put a blob of solder on the fuse and it's working now. Ideally the whole fuse box would be replaced but that's not likely.

Thank you to everyone who chimed in!