EFI and P1300

So, on my 95 taco with a brand new JDM 3rz, been running perfect for a while now, suddenly wouldn’t start one day. Turns out it was the EFI relay (it has over 300k, so makes sense), so I replaced it with an auto store relay and the problem was fixed.

Well the next day it started taking longer to crank and after pulling the key out, the fuel pump would still run for a few seconds. So I finally concluded that the new relay I had was sticking. I should also note the I was getting a p1300 code during this time, but it would run fine. When I cleared the code, I would start the truck and the code would not be there, but when I cut it off and started it again, it reappeared as soon as it cranked up. It did this same thing multiple times.

So I went to Toyota and got a genuine relay, put it in and it went back to normal, fuel pump running normally and starting up like it should. Once I cleared the code, it did not come back for a few days.

But today, the code came back when I cranked it up, even though it cranks fast and runs perfect.

I am waiting on a new igniter to come in, and I have checked the connections between the ECU and igniter and the igniter and distributor (there are no coil packs, just a distributor) and I have cleaned up all grounds, including the igniter ground.

Why would the code be present but run totally fine, and not even trigger the fail safe by cutting off the fuel?

 

You are right on track

IMO disregard ECM(especially if truck still runs)

 

As far as your question about fail safe thingy
Codes just warn/point owners/techs in a direction
Lots of Loadies don’t do crap……bc vehicle still running
Like a miss fire code P0300-P0306
Vehicle will still run…..until it doesn’t
Let everyone know once the part arrives and installed!

 

You likely don’t have an IGF signal.
Or an intermittent wiring issue.
The reason I think it’s an IGF issue is, the truck runs.
No IGT and the truck won’t run.

Do you have a repair manual?
You need to do some testing.

 

Many codes will trigger a "fail safe" mode although some don't affect driveability all that much, IGF circuit problems on Toyota will almost always result in the PCM shutting down the injector(s) on the affected cylinder(s) for as long as the fault is present.

The P1300 code is pretty cut and dry, no IGF signal received by the PCM for 4 consecutive firing events.
As to why it's not triggering the injector cutoff I can only assume that maybe the event is lasting long enough to set the code but not long enough for it to trigger the injector shutdown.

If the truck runs there's really only 3 options it can be:
Open/short in the wiring
Faulty igniter
Faulty PCM

 

Thanks guys,
So I had tried checking continuity between the igniter and ECU originally, but I was going off of some other forums I had read.

I guess I need to go through the procedures that Dm93 posted there and see what the voltages are

 

Alright, so I checked voltages and resistances. The distributor is good on resistances.

There is 0.5 ohms between the IGF terminal of ECU and the igniter connector, so it’s good.

When I checked voltages between the IGF terminal and body ground, I got 0. I also got 0 voltage between IGT terminal and body ground when cranking/key on.

I was getting open line when trying to measure resistance between the IGT terminal and the igniter connector, but I’m assuming that was just my fault, because if there was a short there, it wouldn’t run, right?

Terminal 3 of the igniter connector and body ground shows a full 12 volts, so it’s good.

I guess the ECU is to blame? Weird because it just runs totally fine. I think maybe I should pull it out and look at the inside to see if it’s just a small repair.

Thoughts?

 

I think the computer looks good…

 

The only part that I guess could look suspicious

 

Did you check the IGF circuit for a short to ground?

I'm not sure about 1st gens but on 2nd gens the PCM supplies 5v on the IGF terminal and each coil pulses it to ground when they fire.

 

How would I check that, just continuity? Because it has 0.5 ohms between the connector and the ECU

 

Unplug both ends, set your meter to ohms and check between the IGF circuit at either end and a known good ground. Should read open (OL) or at least greater than 10k ohms.

 

Both ends show open line to a body ground, so it seems good.

What now??

 

Can it somehow be fuel related?

It’s getting fuel fine but the fact that it went away with the relay makes me think it has something to do with that

 

Is that a burned spot next to that capacitor?

 

That’s what I was thinking, but I’m not sure. I don’t have really any experience with circuit boards. My dad looked at it and thought it was ok, but who knows.

 

Should I just get a new ECU?

 

Can you get a better shot of it?
Hard to tell for sure with the lighting.

 

I actually already the it back in the truck just to test some other things, but I got a few pictures

 

Sure looks burnt there but I can't be sure.
I looked at the scope capture in the code guide and it looks like the PCM supplies the 5v for the IGF circuit, so if you have no 5v on the IGF circuit key on with the igniter unplugged and its not shorted to ground the it would seem the PCM is bad.

I'd be curious what fried the board if that's indeed a burn mark, that almost never happens without help.