I would check the fuel pressue is good at a few points in the system and if it is at the right pressure throughout.

With all those items you've checked...I bet you have a weak fuel pump.

 

Checked the fuel pressure when cold at the cold start injector port -- 40psi. I need to double check pressure with the engine hot, but so far it looks like the fuel pump is ok.

What would prevent the injectors from firing only during starting?

 

we don't know if they are firing or they aren't firing... you've done a good job of troubleshooting down to that, and you have possible symptoms indicating that, but it's still speculation.

if you want to talk long shots...

after my truck was down for several months, I put a fully charged battery in it, and it wouldn't hardly turn the starter over... I tried it multiple times... then I decided that I wanted to see if it dimmed the headlights when trying to start it, and wa la, the headlights didn't dim, and it turned over at full speed... been perfect ever since :-/

i'm blaming the ignition switch for that, and i'm wondering if it could be an issue here... you could test for it, by momentarily shorting the starter across with a jumper, while the ignition switch is in the "on" position... but i'd be more inclined to verify your original theory of the injectors not firing when the starter is cranked.

 

WE FINALLY HAVE HARD DATA.

Injectors have perfect fuel pressure and an LED (aka noid light) on the connector shows a signal being sent. But they are NOT firing when the engine is cranking.

Get this: If you bypass the injector solenoid resistor (the ceramic resistor with the cooling fins on the driver's side inner fender) the truck starts and runs perfectly.

This means that the injectors are simply not getting *enough* voltage with the engine cranking. Once the alternator kicks on, it has enough to keep it going.

Bypassing the ignition switch does not help (that is, supplying straight battery voltage to the injector circuit, rather than through the IG switch).

The white and white/red wires to the ECU that power the injectors get a full 12V with the ignition switch on. The dual brown wires that ground the injectors have very good contact with ground. So the ECU has what it needs to fire the injectors.

Right now the likely suspects are:
- Injector solenoid resistor
- ECU

BUT I tried swapping BOTH of these parts from a good running 87 4Runner. Is it possible that the 87 ECU simply won't work with 88 injectors?

 

That's what I understand. 84-87 22R-E injectors are the same, 89-95 are the same, 88 are different than all other years.
https://www.yotatech.com/forums/f37/...l#post52098737

 

I know the 88 injectors are a stand alone year, but would the ECU and injector solenoid be different form an 87? I've never pondered this question...when I get some time I will look up the part numbers on toyotapartszone.

 

The solenoid resistor is the same part number.
http://www.toyotapartszone.com/Page_...er=28515-26030
But the ECUs appear to be specific to each year(exc. 86 & 87 which are the same). Apparently 86-87, 88, and 89 all have different part numbers.
http://www.toyotapartszone.com/Page_...onentsID=84-04

 

I had the hot start problem. I finally dropped the fuel tank and removed the fuel pump and found the problem. There is a short rubber hose in the fuel tank connecting the fuel pump to the fuel line. Mine was hard and totally cracked. The hose must have been spraying fuel inside the tank and letting fuel drain back into the tank. The hot engine probably caused a vapor lock preventing the fuel from getting sent to the injectors because of leaking out the hose. Replacing the 2 inch fuel hose solved the problem.
The hot start problem went away and also the check engine code for overly lean error from the o2 sensor. I wasted my money on a new sensor because of that bad hose. When the tank was out I should have cut an access in the bed to get to the fuel pump without having to drop the tank.
Be sure to be very careful with the fuel tank and do the work outside to prevent fumes and fires. No Smoking. Do not die.

 

Swapped out the ECU with an identical 88 one -- no change.

Got a separate injector resistor also. This one was the wrong part # but a very similar Denso unit. It read 2 ohms rather than 3 ohms so I adapted it to see if it would make a difference -- no change.

Again, bypassing the injector resistor allows the truck to start easily. But it's not safe to run it that way for more than a few seconds.

I will continue by taking another look at ground wires and make sure there's not a big voltage drop across the ignition switch. If I can't find the issue I will hook up a relay across the injector resistor to bypass it when the key is in the start position. This will at least be a bandaid until I can figure it out.

 

Read this thread...especially post number 48.

There is a splice in the wiring harness between injector 2 & 3 that can fail...

This is the only other thing I can think of...

http://forum.ih8mud.com/79-95-toyota...gremlin-3.html

 

Turns out it was a bad ground. I hadn't paid attention to my ground wires for a long time. I was missing one from the back of the head to the firewall. Also the main engine ground was in the wrong place and its connection to the terminal was crummy.

It now starts super fast and the problem is fixed.

The moral of this story: check your grounds!!! Take an ohmmeter and check resistance between battery negative and many points on the block, head, intake, body and look for negligible resistance. I had about 2 ohms of resistance and it caused this issue and sluggish starting.

Thanks for the help everyone.

 

Those pesky bad grounds strike again. Glad it's back running good.

 

That would be plenty to cause your problems.

Your advice to check resistance from the battery negative to various points is especially good. More effective than "check your grounds" ... for what?

 

Also a big thank you to superbleeder for his comprehensive writeup on the location of 22RE engine grounds. It's a great reference. "Gotta check 'em all!"