91 - starts, runs 5 sec & dies; no fuel - Toyota Nation Forum : Toyota Car and Truck Forums

Tekman2u · 11-02-2009, 12:08 AM

Spent another whole frigging day trying to help a poor neighbor kid trying to get his "free" first car (91 Corolla) running, and could really use some help from Toyota experts. He got the car free because it needed a fuel pump and a starter, which I helped him replace. After driving it for 3 weeks, it died suddenly. EFI fuses were blown. Replaced fuses, and car starts, runs for 5 seconds, and dies. Starts immediately, then dies again. NO FAULT CODES. Tested the normal stuff - fuel pump works fine when jumped at diagnostic connector (Fp to B+), and fuel pressure is within spec. Tested EFI relay, Circuit opening relay (good), and worked through all the other diagnostic trees on the A-1 through A-7 charts. This car does not have a MAF sensor. Tested fuel pump (and COR), and have power to fuel pump (and COR) when cranking, but not when switch is in ON position. Seems like the only thing I haven't checked is ECM, but am concerned that I don't yet know what tells the fuel pump to stay on when COR is out of crank mode. Seems like a common 6th gen problem (looking in archives), but only tips I saw were COR and MAF. Maddening thing is it runs like a sewing machine when first started (and when fuel pump is jumpered). This is probably a simple "DOH!" fix, and I'd like to get this kid running again, but could sure use some help!

voganni · 11-02-2009, 12:29 AM

My wiring diagram shows two relay coils in the COR relay, one energised by the starter, and the other one, with the green-red wire, energised by the ECM. The ECM is supposed to turn on the relay when detecting that the igniter is firing. I would check for continuity in the relay coil that goes to the ecm, and that you have 12 volts from the ecm after engine start (in your 5 second window!). The 4afe engine does not have a MAP sensor, only a vacuum sensor. 4age does use a MAP sensor. Others on this forum know lots more, hopefully they'll step up. C'mon guys!

Tekman2u · 11-02-2009, 08:47 PM

Thanks! I got a better quality wiring diagram, and confirmed what you said, with one exception. During start, one "coil" in the relay is energized by the starter solenoid, and passes current to the fuel pump. That is WORKING. In "run" mode, the other coil inthe relay is energized via the Black/Red wire from the EFI relay. The "Fc" terminal of the ECM (green/red wire) is actually supposed to supply the ground to energize that second coil, and allow current from the Black/Red wire pass to the fuel pump. My ECM is not switching to ground when the car is running. Can't yet figure out if the ECM is bad, or if the electrical widget that tells the ECM the car running isn't giving the ECM the signal. My book talks about the ECM only continuing to supply the fuel pump if it gets a signal that the car is running, but doesn't tell me what that input is. In other models, it was a switch in the MAF (which to book DOES cover :? ). Anybody know what that trigger is on a 4age motor with a MAP instead of a MAF? I'd really like to not spend $250 on an ECM that this kid doesn't have if it is an igniter in the distributor, or something else. I have checked the MAP sensor and Air Intake sensor, and they are good.

Donald · 11-02-2009, 09:23 PM

Check the throttle position sensor, and the MAP sensor.

My first guess is that the vacuum line to the MAP sensor fell off, or is broken (easiest thing to check)

voganni · 11-02-2009, 10:22 PM

Sorry, I thought you had a 4afe. You are correct that the green-red is a ground path. On the 4age, my wiring diagram shows that green-red being grounded via the airflow sensor, the brown wire being connected to ground. So looks like your ECM is not at fault anyway! I would check that the brown wire on the airflow sensor is grounded, and that the green-red wire is getting grounded when the engine starts. If not, it's the airflow sensor. If so, it'd be the COR relay.

Tekman2u · 11-03-2009, 12:00 AM

Jumpered the feed to the circuit opening relay that should be providing ground (Fc from the ECM) to a known ground, and the car started and ran like normal. Pulled the ECM out (why does Toyota BURY this so deep?!!), and discovered that it has removable covers on top and bottom of the ECM. Upon removal, it was easy to identify a couple of burned "threads" in the printed circuit board, one of which connects the Fc terminal to the "ground bus" on the circuit board. At least I know for sure why the ECM wasn't giving the input to the circuit opening relay it was supposed to. I would STILL like to know what inputs the ECM needs to make the Fc switch to ground.

voganni · 11-03-2009, 12:01 PM

Somebody else a while back said it senses the igniter is firing and turns on that ground circuit. You could probably repair the circuit board with a small soldering iron. I've done it on other boards. ECU's are probably pretty cheap in junkyards though. Good investigative work!

Donald · 11-03-2009, 01:12 PM

Quote:

Originally Posted by voganni

Sorry, I thought you had a 4afe. You are correct that the green-red is a ground path. On the 4age, my wiring diagram shows that green-red being grounded via the airflow sensor, the brown wire being connected to ground. So looks like your ECM is not at fault anyway! I would check that the brown wire on the airflow sensor is grounded, and that the green-red wire is getting grounded when the engine starts. If not, it's the airflow sensor. If so, it'd be the COR relay.

Oops! I made the same mistake, not reading all the way.

Quote:

Originally Posted by voganni

Somebody else a while back said it senses the igniter is firing and turns on that ground circuit.

Yes.

Some systems need oil pressure also, (Paseo/Tercel) or the fuel pump will shut off after a few seconds.
I think the idea is if the car crashes into something, (engine stops) they don't want the fuel pump running, incase there is a broken line.