Hello, need help on a 3vze injector pulse issue.

I have a 1990 4runner and walked out one day to start it up and it would crank all day but not fire up. It ran great for months up untill now. I have fuel pressue at the the rails and good spark. Timing belt is also new. So far i've settled on a no injector pulse issue based on the fact that the spark plugs are dry even after cranking and cranking. Put a multimeter on the distributor output wires and they all are in spec. Tested the relay and checked all the fuses as well. I still need to test the ecu I suppose but am not entirely sure how to do that. Any write ups on how to specifically test the ecu? Also what else am I missing? The issue seems to be electrical so it seems there's plenty to miss.

 

Oh, also pulled the plenum and tested all the injectors which all were good. A coworker noted that if the tach isn't reading while cranking the motor (which it is not) it could be a crank position or cam position sensor issue. Though I thought those were contained in the distributor unit.

 

Welcome to YotaTech.

As you thought, the "cam position sensor" is the G coil in the distributor. So if you have good spark, the ECM is getting the G signal (something else is wrong with your tach).

You could check for injector signal with a "noid" light. (Better yet, a "12v" LED (an LED with an integral resistor), but you have to watch polarity.) Just so you know, all 6 injectors open at the same time. One side is at battery voltage, and the ECM very briefly grounds the other side to open the injector.

How do you know you have good spark? (The reliable/easy way is to put the inductive pickup of your timing light on each plug wire; if the light flashes, you have spark.)

How do you know you have "good" fuel pressure? (Please don't say you "cracked" a fuel connection. If you did that, you need to go back and replace those two crush washers: one time use.)

"Tested the relay and checked all fuses." My favorite line. Which relay did you check? (there are a lot of them, even in a 31-yr-old truck) Which fuses did you check? You don't even know where "all" of them are.

 

I checked fuel pressure by jumping b+ and Fp and watching fuel pump out the return side of the fpr. I suppose that's more fuel delivery than pressure but I dont have a guage.

The relay I checked is the efi relay, I swapped it with another relay too just to double check but it had no effect. Also checked both of them with a multimeter. I checked all the fuses under the hood and at the driverside kick panel, particularly the efi and ign fuses. Non of the ones I found anywhere had failed, if there are more fuses and relays tucked away somewhere that are critical to the efi system please enlighten me.

Spark was checked via pulling the plug wires one by one and grounding them to the vehicle. Based on the lack of fuel smell and dry plugs though I am assuming spark is not my issue. Also the resistance across + and - on the coil checked out and I replaced the ignitor.

I'll pick up some NOIDS tomorrow on the way home from work to make sure injector pulse is/isnt happening.
My other / original question is how do I test my ecu to rule it out as the issue?

Cheers and thanks

 

Okay, those are (mostly) good tests and you're making progress. Based on the tests you described, you know the fuel pump will run when the COR is bypassed, but you don't know if the fuel pump runs when you're just trying to start your truck. Here's what you need to know for the usual failure mode: https://www.yotatech.com/forums/f116...-quits-312747/ Usually, this is very easy to diagnose: try to start your truck with the jumper in. If it starts then, you know you have a problem in the VAF-COR circuit.

[The COR has two coils, and the more common failure mode is "starts and quits after a few seconds." But you could have had the start coil not working for a long time and just had long-crank until the VAF coil quit. Or some bad guy stole your COR. But the tests in the post cited will take you where you need to go.]

Except you have the plenum off, and you're thinking of testing for injector pulse. Go ahead if you want, but my money is on "pump not running."

I'm not sure how you test for spark by grounding a plug wire to the vehicle (grounding a plug wire can damage the coil and igniter). If you mean holding the plug end near a ground and looking for spark, you're not doing the plug wire any good. You can do the same test by putting a spark plug in the plug wire and using that, but the easy way is using your timing light. A timing light is $30, and you need one anyway. Don't skip the simple tests (checking for spark) by "assuming" you have good spark because you can't smell fuel.

I don't know of any reasonable way to directly "test the ECM." In the FSM, "replace the ECM" is usually after you've eliminated a long list of other possibilities. An ECM failure is really rare, and there is a long list of things that are much more likely to fail than the ECM.

Last, run the tests. The Parts Cannon just doesn't work. You've already replaced a few parts (EFI relay and Igniter) that were almost certainly good.

 

With Fp and B+ jumped it still will not start. I'll probably run through the checks in that writeup (which is a good one thank you) just because I can, trying to rule out everything.

 

Dude, the guy was simply asking for some sort of way to test the ECM if possible. Not your armchair diag.