[WeirdAl1999]

My 91 VR4 has a crank no start issue. Fuel pressure and spark and all 6 plugs. Pulled the injectors, they are clean, I tested their spray using a can of carb cleaner. I hooked up a noid light to the injector harness, the noid light is flashing, but extremely dim. The filament is glowing a bit, but it can only be seen from up close, and not when its bright out. The ECU is receiving good chassis ground, I checked pins 72, 13, and 26, they all have good grounds. So I did some experimenting. I am assuming the the injectors receive constant positive signal with the key on, so I checked the resistance between between the positive on the injector harness and the battery positive, it was pretty high, I don't remember what exactly. So I hook one side of the noid light to the ground side of the fuel injector harness, and hook up the other side to the battery positive. And that made the noid light flash very bright while cranking. So can I assume that the injectors are receiving good ground pulse from the ECU? And if so, where could the problem be in the wiring. What gives a +12V to the injector harness?
Thanks, Al

 

[box]

You seem to have a sound grasp on electrical diagnostics Al, get yourself the workshop manual here and familiarise yourself with the circuit diagram.

The power supply to the injectors comes from the MFI relay, via the injector resistor.

 

[Black&Tan]

Wouldn't the injector resistance pack increase resistance between harness and battery positive?

Pull your ECU and visually inspect it. If it looks fine, check voltage from positive to negative terminals on injector plugs with key on. It should read 12 volts.

I had a similar issue on my NA and it was my ECU. IIRC I was getting weird readings at the injector plugs with key on (3v, 6v, etc). My fuel injector circuit was burned in a way that was really hard to see until I looked close and it was partially grounding out causing my noid lights to dim and was causing a rich condition.

If it's your ECU check your IAC. Mine shorted and took out my ECU.

 

[mothsmoths]

My 91 VR4 has a crank no start issue. Fuel pressure and spark and all 6 plugs. Pulled the injectors, they are clean, I tested their spray using a can of carb cleaner. I hooked up a noid light to the injector harness, the noid light is flashing, but extremely dim. The filament is glowing a bit, but it can only be seen from up close, and not when its bright out. The ECU is receiving good chassis ground, I checked pins 72, 13, and 26, they all have good grounds. So I did some experimenting. I am assuming the the injectors receive constant positive signal with the key on, so I checked the resistance between between the positive on the injector harness and the battery positive, it was pretty high, I don't remember what exactly. So I hook one side of the noid light to the ground side of the fuel injector harness, and hook up the other side to the battery positive. And that made the noid light flash very bright while cranking. So can I assume that the injectors are receiving good ground pulse from the ECU? And if so, where could the problem be in the wiring. What gives a +12V to the injector harness?
Thanks, Al

You have asked a bunch of different questions, I'll try to answer some of them. The TT uses injectors that are termed "low impedance/resistance" while the NA uses "high impedance/resistance" fuel injectors. To prevent damage to the TT injector's internal coils or their power/ground circuits due to higher currents and heat from the low impedance, there is a resister pack that safely drops the input battery power current/amps and distributes it into 6 individual wires for the 6 injectors. So the voltage remains relatively unchanged at each injector, but the amperage is reduced which is why the noid light is dimmer, but still blinks if the ECU supplies the ground signal appropriately. Some measured resistance is expected as you found. Measuring the voltage input at each injector or the rear harness connector should show battery voltage s that are all very close. Confirming the noid blink on each confirms the computer grounding for each. Remember, it tells you nothing about the injectors condition, proper injection timing, proper volume injected, or if the fuel rail pressure is proper. Pull some spark plugs...are they wet? what is the measured pressure...not "seems OK". Your ECU is a mess as I said before. It didn't work before you took to in, you were surprised it got fixed.... ???still may not work. Put crank pulley timing notch on T, then pull cam gear covers and check all 4 timing marks on cams. If OK there, hook up the timing light and check base timing as described in the service manual @box linked you into.
Don

 

[WeirdAl1999]

You have asked a bunch of different questions, I'll try to answer some of them. The TT uses injectors that are termed "low impedance/resistance" while the NA uses "high impedance/resistance" fuel injectors. To prevent damage to the TT injector's internal coils or their power/ground circuits due to higher currents and heat from the low impedance, there is a resister pack that safely drops the input battery power current/amps and distributes it into 6 individual wires for the 6 injectors. So the voltage remains relatively unchanged at each injector, but the amperage is reduced which is why the noid light is dimmer, but still blinks if the ECU supplies the ground signal appropriately. Some measured resistance is expected as you found. Measuring the voltage input at each injector or the rear harness connector should show battery voltage s that are all very close. Confirming the noid blink on each confirms the computer grounding for each. Remember, it tells you nothing about the injectors condition, proper injection timing, proper volume injected, or if the fuel rail pressure is proper. Pull some spark plugs...are they wet? what is the measured pressure...not "seems OK". Your ECU is a mess as I said before. It didn't work before you took to in, you were surprised it got fixed.... ???still may not work. Put crank pulley timing notch on T, then pull cam gear covers and check all 4 timing marks on cams. If OK there, hook up the timing light and check base timing as described in the service manual @box linked you into.
Don

Thank you for all the replies, I apologize for the delayed response. You are right Don, I should check the fuel pressure for an actual value, the way I checked for "fuel pressure" is by undoing the fuel inlet at the rail and seeing fuel squirt out. Once it warms up here, I am going to put in another fuel pump I have had, it came from my DSM, I just changed it out as preventative maintenance, but it was working perfectly fine when I took it out. I know for a fact the injectors themselves are good, as I rigged up a bench test using a can of carb cleaner. The timing on the crank pully is fairly in line with the front 2 cams, visually looks like less than 1 tooth off, I haven't checked the rear cams yet. (it's 20 degrees outside currently so not anytime soon probably) I'm not sure if I mentioned this previously, but the car runs if I spray starting fluid into the intake. Thank you for the input,
Al

 

[Black&Tan]

Thank you for all the replies, I apologize for the delayed response. You are right Don, I should check the fuel pressure for an actual value, the way I checked for "fuel pressure" is by undoing the fuel inlet at the rail and seeing fuel squirt out. Once it warms up here, I am going to put in another fuel pump I have had, it came from my DSM, I just changed it out as preventative maintenance, but it was working perfectly fine when I took it out. I know for a fact the injectors themselves are good, as I rigged up a bench test using a can of carb cleaner. The timing on the crank pully is fairly in line with the front 2 cams, visually looks like less than 1 tooth off, I haven't checked the rear cams yet. (it's 20 degrees outside currently so not anytime soon probably) I'm not sure if I mentioned this previously, but the car runs if I spray starting fluid into the intake. Thank you for the input,
Al

There's no fuel pressure test port on these cars.

3sx sells a port with a gauge that fits on the end of your fuel rail. I have one and it works good. If you get the hydraulic one make sure you cut the nipple off or it will give inaccurate readings when the car is warm.

You should check fuel pressure before replacing pump and see what it's doing. Also check the regulator. Way easier than dealing with busted fuel pump housing bolts and frozen fuel lines.

And did you check your ECU?

Don't disregard it. My injectors flowed fine on the bench. I spent hours troubleshooting my rich fuel issue and ignoring my ECU because it was less than a couple years old.

It was my ECU. The fuel circuits are a common failure point. Fucking remans.