1987 4runner SR5 5speed, truck is bone stock with little to no modifications, purchased non running a few years ago and finally getting to resolving its issues. Truck has not run since in my possession for it needed a short block. Spent thousands of dollars to finally button this truck up only to find out it has an injector pulse issue.
Issue: No fuel injector pulse. injectors not firing, confirmed with a noid light

Diagnostic: inspected the full wire harness for breaks or bad connections to terminals #10 and #20, tested voltage readings directly at the ecu to determine 12v on both of these terminals, ground should be applied by ecu when engine is cranking/ running.
also thoroughly inspected all engine grounds.
!To shorten this post!
I printed out 2 exact sheets of ecu pin outs and directly compared voltage readings from this non running truck, to a known good running and driving truck of exact year and exact part numbers. No major deviations between the two documented readings.

Parts with exact part numbers I had swapped between the known GOOD running truck, and this NON running truck. Disclaimer, both trucks are 87 4runners:
FULL ENGINE WIRE HARNESS
DISTRIBUTOR
ECU
IGNITER w IGNITION COIL
AFM
EFI MAIN RELAY
CIRCUIT OPENING RELAY
INSTALLED AND CALIBRATED NEW TPS
REPLACED 80 fusible link(didn’t need replacing, figured it wouldn’t hurt)
(May be forgetting some at the moment)
Grounds are good, no if ands or buts. not only tested for resistance values but can 100% confirm every ground on the ecu is good.
Can confirm voltage at terminals B1+B+ for the main relay
Can confirm Battery B+ voltage is good at 12v
To add:
Fuel pump runs unjumpered and jumpered
Fuel pressure is 38-42psi with new fuel pump and filter
Compression is good
Good healthy spark from ignition coil, and from distributor. Distributor is appropriately clocked and timed.
Cold start injector works
All essential connections on the engine wire harness are in good connection.
NO FUSES BLOWN this includes Engine, and EFI
Engine cranks, sparks, just no injector pulse
I get appropriate signals from IGF, NE, and IGT as well
And 5v reference to afm and to throttle position sensor
Resistance at distributor is within spec at 170ohms

Thank you for taking your time to read this post. I know injector pulse threads are dime a dozen, Ive owned 6 of these trucks now, and take extreme care and attention to detail with each and every one, i really look forward to having this truck back on the road

 

Wow! It sounds like you know your stuff.

How did you test the signals (IGF, NE, IGT, and injector pulse)? I have to use an oscilloscope to pick up IGF; if you used an oscilloscope on pins 10 and 20 I am convinced you have no pulse.

The only condition I know of that supresses the injector pulse is the lack of IGF, but that takes a few revolutions of the crank so it should not affect starting. (Of course, NE is essential.)

 

I have not tested with an oscilloscope yet, that was my very next step in all of this, Im going to try to find a decent one and check back. I work as a certified technician at Toyota, i was able to tow the truck to the shop to work on it in free time and pick the brains from the master techs that worked on these trucks when they were new and they well all stumped, kind of a bummer. Now i have the truck in front of my house making interchanging parts and research a lot easier to test. Ill try my best to get a oscilloscope and report back.

 

It’s been a few weeks since my original post, I’ve made a discovery that changes everything. I ran multiple tests and inspected just about everything once again, I then decided to unplug all four injector wires and test injector pulse with a noid light, I had injector pulse! Sweet! Then I proceeded to swap injectors from a known good, same year, truck and still nothing. Same issue, no injection pulse when testing with only one injector unplugged, injection pulse when all the injectors unplugged.
resistor swapped and tested good from a known good truck, grounds are tight with resistance checks within spec. I am lost.
still have yet to get my hands on a scope, with this new discovery I’m not sure how much a scope will tell me.

any help is greatly appreciated

 

Hey Trav. So what came of your issues? Any solutions?

 

A few months back I was stumped on injector pulse issue, I don’t exactly remember at what point I came to my resolution, but if I unplugged all four injector wires I did in fact have injection pulse on my noid light. Extremely dim but the pulse was there. Again not certain at what step of resolved my issue.

but I decided to try the basics one last time for perhaps I missed something upon initial testing. Sure enough the answer was right in front of me. I performed a leak down test to find out the exhaust valves in every cylinder were leaking, BAD. I just put that engine in. But was short sighted on ensuring the cylinder head I reused upon build may not have been on the best condition. Nevertheless I had a spare head laying around, lapped valves, cleaned the head and installed new valve seals. Boom started up flawlessly. The truck is now back on the road as desired.

I do feel somewhat uneasy with myself for I should have found this earlier.

there were many issues with the trucks wiring however, and all my testing verified the trucks electrical components are in good health.

moral of the story:
basics first

 

That leaves me a little confused. The injector pulse and valves were unrelated issues, correct?

 

Correct, my engine would not run due to valves not sealing.

at some point I did NOT have injection pulse, I’m not exactly sure at what point I fixed the issue. I did have an issue with the wiring between the 80a main and the battery. To remedy that I replaced the 80a fusible link, replaced the wire to the battery, and replaced the terminal to the battery. Again I’m unsure if this is what resolved my injection pulse issue, but around the time of the repair mentioned previously in this paragraph, my injection pulse was found and noted.

ive Definitely learned a ton in the months studying and researching injection pulse. If there’s anything I can help with please let me know and I’ll do my best to assist.

 

Thanks! That clears that up. I've just rebuilt the engine in an 86 4runner that say for 15 years or so and have a no start. Runs on the cold start injector a second and dies. I have it down to a weak pulse and am currently chasing allllll the crusty connections​​.
Funny you mentioned the 80amp fuse and link wire as I got my parts and was working on replacing those today(got chased inside...the open barn I'm working in was just too damn cold.) Hopefully I can finish up the connections and get it all back together for a test while I'm off for the holidays.
Thanks again for posting your process in this thread, replying back and offering up advice!
Cheers!

 

check for corrosion inside the harness: https://www.yotatech.com/forums/f116...t-help-303272/

my '86 had that problem, it was a nightmare to figure out

 

Oh yes! I've fought with the wiring harness years ago. Randomly would run like poop. Accidently found the issue poking around the intake and moved the harness. The single to double injector connection was hanging on by a couple strands.
I'm currently going through everything in the harness, fusible links, etc and just replacing them. Can't wait to put it all back together and give it go!!
Thanks for the link!