2001 Open Circuit Relay difficulty

Hey guys,

First time post here, any ideas would be much appreciated as I’m getting to my wits end. Here’s a quick version of the past couple days

• 2001 Tacoma 3.4l drives all day, after a stop for gas it cranks over but won’t fire up. Can’t hear the fuel pump running. Has spark.
• Determine that EFI relay is working properly
• Determine that Open Circuit relay is not working properly
• Am able to use a paper clip to “jump” the Open Circuit relay receptacle and send power to the fuel pump, pump runs, truck starts.
• Determine that a bad ground from the ECM to the Open Circuit relay is causing problems, not allowing the relay to perform.
• Decide to cut into the ground wire and ground it to a bolt in the cab, so at least I can power the pump and drive the truck while I figure out what to do about the ECM.
• Wire is newly ground, pump receives power and runs, but truck only cranks, will not start now. Still have spark
• Did cutting that wire effect some other fuel signal for starting up? Any ideas? Thanks very much for any thoughts.

 

I wouldn't go cutting wires and such until I looked at a wiring diagram and thoroughly understood how the circuit worked. (Maybe you already did this.)

First, maybe you blew a fuse.

I believe Toyota generally has a wire FC from the relay to the computer, then a transistor in the computer grounds the FC wire when the engine is running (computer receiving NE signal from crank sensor).

Are you saying you grounded this FC wire then reinstalled the relay?

And how could you hear the pump not running? It's hard to hear when the engine is cranking and when the engine is not spinning the pump won't run. You can remove the starter relay, then you can hear the pump when key is turned to START.

And usually if there is a problem with the circuit opening relay working with engine running, it will still work while engine is cranking, so you'll have fuel pressure for a few seconds, engine will start then die after a couple seconds.

 

Thanks for the response DrZ, I have the full wiring schematic book for that truck so no worries there.

The fuses are all good, nothing has been blown yet.

The FC wire is the one that I grounded, correct. And the one that seems to now be influencing more than just the Open Circuit relay.

The pump will kick in for a short second or so when the key is turned to START, then turn off, that’s how I could initially tell it wasn’t engaging when the truck initially failed. I had a friend work the key, and I got under the truck with my ear against the tank. It’s a fairly audible pump.

 

You tested the relay by following the procedure in the repair manual? "Inspect relay continuity" 3 tests and "Inspect relay operation" 2 tests?

Then see the Fuel Pump Control Circuit section and follow the test procedure there. Specifically, you should test for voltage at the FC wire. Disconnect the FC wire from where you grounded it, turn the key to ON, then measure voltage (from wire to ground). It should be 9-14 volts. This is basically the same test in the repair manual when the wire is still connected to the ECU.

 

The PCM's on these trucks are pretty bullet proof but you might have the one that has issues. On the intake manifold ALL of the grounds for the PCM come together, should be by Toyotas Data link connector... give them a wiggle and see if any break. There is another ground on the passenger side head in the back that goes to the firewall too. As stated before, the fuel pump only runs when the PCM gets the cranking signal and while it is running... Do you have a tach? I am curious to know that if you do have a tach does the tach move slightly when it cranks and does not start? I am trying see if the signal from the crankshaft position sensor is there. Some vehicles I work on if the CKP, crank position sensor, is bad, the tach wont wiggle during cranking and if it is a known issue, you check the CKP first.

 

Guys thanks for your help...

DrZ, I don’t have the repair manual, I’m primarily operating on trial and error techniques. I’ll get my multimeter up and running tomorrow... (dead battery)

Glamisman, I located the two grounds you’re talking about, both seem fairly secure, nothing looking out of the ordinary... but you never know. I also used the wiring diagrams to inspect some others which all looked good. So my tachometer does not jump or even wiggle when the starter is cranking, tried that today.

I pulled the wiring off one of the fuel injectors to test with the test light, and it’s not getting a ground to it from the ECM when the engine is cranking... so pretty similar issue as with the open circuit relay (it seems). I’d like to take a closer look at the wiring for the CKP, its a little tricky to pull off, but maybe I’ll just commit to it tomorrow.

 

If you have a smart phone or an iPad you can buy a pretty good OBDII scanner for under $100. With this you can see if there are any codes or any pending codes. Not all codes with cause the CEL (check engine light) to illuminate. Any recomendation by me of which scanner to use is going to start a scanner debate and that is not why you posted.

There any easy checks. At this point the only thing that I can think of is to wire in a single filament bulb, test light will do the same, off the circuit opening relay on the wire that goes to the pump and give it enough wire to put it somewhere out of the way and just drive the truck. When she doesnt start you can see if the light lights. If the light lights and you dont hear the pump I would smack the fuel tank. I have seen where the electrical connector for the fuel pump gets corroded and melts.

 

I just went out and checked my 98 Tacoma and the tach doesnt move until the engine actually starts... that was a false lead.

 

Hey guys, so just to update incase it’s of use to anyone else. My FC wire ended up being bad between the Circuit Open Relay and the ECM, so I replaced that. That allowed for the signal to reach the fuel pump when cranking starts. However, the truck would still not start, or would start and shut down after a couple minutes. I was able to borrow a buddies ECM out of his 2000 Tacoma and throw it in today, truck runs great. I haven’t extensively tested it, but it starts, idles, drives, etc perfectly. I haven’t worked out the relationship between that bad wire and the bad ECM yet, but there you go. Thanks for your suggestions.

 

Maybe take the cover off your ECM and check for a bad transistor leading to the FC pin. Also look for bad capacitors. Transistors can be electronically tested in circuit. Capacitors usually can't be tested in circuit unless you have an ESR meter, but a lot of times bad electrolytic capacitors will have a bulging top on the cylinder, so you can spot them visually.

 

Hey guys. I realize this is an old thread but... I'm trying to get around buying a new open circut relay. I can use a jumper wire and get the truck started and I can pull the wire after I get it started and it will still run. So I know that once you get it started that the relay switches over to a different contact. The one that goes to the air box. But which terminal is the one that activates during cranking to let the fuel pump activate? Cause without the jumper my fuel pump will not work. I'm just wandering if I replace the capacitor in the relay if that will fix the relay instead of having to buy another one. I tested the relay according to my Hayes manual and everything ohm right and then I put voltage to SAT and E and it clicked but then the manual says to put voltage to B and Fp and says to check those same two for continuity. Which must be a misprint. Should it click when you put voltage to those two also? Cause mine won't. I'm thinking my Fp terminal is bad. Cause I can jump them at the diagnostic box and it starts . And I can pull out the jumper after it starts and it will still run. Which tells me that part of the relay is working. ? Any body know for sure about what the relay does or don't do with a bad capacitor?

 

Bump

 

Best to get a copy of the wiring diagram for this circuit for this year. Seems like Toyota changes wiring slightly though the years 1996-2004.

Bridging +B and Fp and turning key to ON should bypass the circuit opening relay and power the fuel pump directly, but Toyota didn't include the terminal on the Fp hole on some models even though it is still labeled.

Sounds like it's easiest to just replace the circuit opening relay if you know it is bad. You can remove the old one and test it first.

 

there is a YouTube video out there where a guy uses a 5 pin Bosch relay to do the job of the circuit opening relay. I advise caution as you are dealing transistors in the PCM... besides, a used Toyota relay is under $40 on eBay and under $100 new.