No injector pulse no start

I have a 90 cherokee. I just swapped in a motor from a 92 and got it running. I drove it around my property (5 acres) a bunch starting turning it off multiple times. I then got on the highway and only made it 2 miles from home and the engine died and I coasted to a stop. I couldn't get it back into park for a bit because something on the new steering column I put in was blocking it from shifting, but after a little under dash wire wiggling it went back into park.

Since then I have checked everything trying to get it started. I fresheners up the dipstick ground, put in a new duralast distributor, checked I was getting the correct resistance on the crank sensor and was getting a propper AC voltage from it when cranking, checked continuity on the wires from the cam sensor in the distributor to the ECU as well as the wiring from the crank sensor to the ECU and the same from the injectors too. I have 35 lbs of fuel pressure. The map sensor checked ok but I don't have a vacuum gauge to check that part. The TPS measured 5 volts where it was supposed to but practically 0 volts where it was to measure .8 when closed so i adjusted it to measure the .8 volts. The fuel pump ballast resistor measured like 4-5 ohms. The engine will run if I spray cleaner in the air intake while cranking, and I have good consistent spark with the new distributor.

So I thought it had to be the ECU, a co-worker thought so too as did Cal. So I got an 89 ECU from a wrecking yard and tried cranking it over and still no starting...

I don't think its the NSS as it will crank, and I'm not sure if there is an ASD on the renix system but I didnt see one. What else could it be?

Interesting problem. Based on what you have done so far, buy or borrow a NOID light and see if the wiring harness connectors are getting the firing signal to the injectors.

http://www.naxja.org/forum/showthread.php?t=1092737

If the injectors are not firing that narrows it WAY down.

If they are firing, then you are getting too little fuel (recheck pressure while cranking) or too much air to get lift off, ignition, and thus there may be a huge vacuum leak or IAC valve stuck too far open, throttle body gasket leak or B+ relay issue.

RE-check all or most of your prior tests to make sure they are repeatable.

I recently read a post here by 8MUD on the fuel pump power routing in run/pre crank, then in Crank, then in running mode and there are three different power paths for the fuel at those three stages, so check the fuel pressure while cranking with your gauge and make sure the pressure stays in the 29-39 PSI range while cranking.

Does it fire while cranking then die immediately in run, or only fires while cranking with cleaner spray into the intake?

Does it run in run mode with cleaner sprayed into the intake?

Does the CPS put out at least 0.50 Volts AC while cranking?

I borrowed noid lights from my co-worker (races poor boys cherokee in ultra 4) and there was no injector pulse. Since I replaced ECU I havent tried the noid lights as I returned them.

The fuel gauge showed 35 lbs of pressure after I stopped cranking until I released it. Didnt check it while cranking.

I only tried spraying while cranking, didnt keep spraying long enough to keep it running in the run position. I also swapped out ignition switches to see if it was the problem with no improvement.

I planned on rechecking sensors this afternoon when I get the running around done

I may have the answer for you, according to an old post by 8mud

"The *Renix* pulses on the plus side and all the injectors have a common ground. Maybe ohm test the ground at injector 1, that ground circuit goes through a bunch of splices. It is my understanding all the injectors have separate drivers, all failing is unlikely. They all do share a common ground."

The sensor and injector and IAC control grounds in the harness to the sensors and injectors piggy back on each other with 25 year old crimps that wiggle loose with age. Cruiser54 has a website and Renix fix pages up here and there on the internet and in many posts here that cover opening up the harness and soldering those crimps to fix the ground issues. I just by passed my bad ones with a direct run to the battery. Mine were on the TPS.

Your earlier issue with the TPS 0-volts at idle, may have been the first sign that the injector ground is your issue.

The same thread I got the 8mud comments form also later says

"What I do not have is fuel pressure while the jeep is cranking! With the key in the run position I have pressure on the rail but as soon as I crank it I lose pressure."

So check that too. But money is on a bad injector ground now.

I did check injector ground with other side of ohmmeter on the battery ground terminal and only had .1 ohm. I did pull apart the wiring harness to the crimp and checked ground there too. It was good, but tried to solder them all together but my iron wouldn't get hot enough to do a good job with all that mass. I do plan on checking tps again but still running around. I have a better "Weller" soldering iron but need to buy new tip.

ECU injector feed runs to pins D10 and c11 at the ECU. That feed comes from terminal 87 of the fuel pump relay.

http://i1354.photobucket.com/albums/q690/cruiser54/Jeep Tech Photos/renixrelaycenter.jpg

If the common stuff (grounds) doesn't work out for you, take a look at the MAP. I bent a MAP pin and my injectors shut down. Straightened the pin up and all was well.

Read someplace that if the MAP doesn't get a reference signal (barometric pressure) the ECU will shut down the injectors.

Or like Cruiser said you may have a power in issue or even a MAP wiring issue?

It was suggested I try starting the jeep with the map and tps unplugged so they wouldn't give the ECU a signal like the throttle was fully open and turn off the injectors. Well it didn't work but I'm not sure if it would start without those sensors giving a signal in the first place.

GroversXJ said:

It was suggested I try starting the jeep with the map and tps unplugged so they wouldn't give the ECU a signal like the throttle was fully open and turn off the injectors. Well it didn't work but I'm not sure if it would start without those sensors giving a signal in the first place.

Click to expand...

IIRC they will not start with out a MAP reading. TPS, O2 sensor are not needed to start. CPS must work and work right to start. This is true on Renix, not sure about HOs.

It looks like my map sensor has 5 volts on terminal c which is reference, but on terminal b there is no voltage at all. This it with the key on but engine not running (by back probing the connector). So I believe that means I need a new map sensor right?

Never mind, I tried again and got 4.39 volts.
Must not have been making contact.
I connected a syringe to the vaccume port on the map and was able to get the output voltage to change from the 4.39 down to 3.6 volts as I pulled more vaccume and then return to reference when I let off the vaccume. So it should be good.

would the ecu still give out spark if the sensors are bad? i think its a ground issue on the injectors. unplug one of the injectors and check for ground that way.

90xj06 said:

would the ecu still give out spark if the sensors are bad? i think its a ground issue on the injectors. unplug one of the injectors and check for ground that way.

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The only critical parts for spark, sensor wise are the CPS and the MAP on the Renix, I think the HO also needs the Dizzy Cam sensor working.

But if he has spark and no injector pulse, it must be the ECU or wiring to the injectors including the ground I think.

As I said before, you must be missing a good ground to the Renix Injectors, either loos crimp inside the harness (know to happen, even considered common), or you missed something at the dip stick ground that needs fixing again.

From an old 8MUD post here:
""The *Renix* pulses on the plus side and all the injectors have a common ground. Maybe ohm test the ground at injector 1, that ground circuit goes through a bunch of splices. It is my understanding all the injectors have separate drivers, all failing is unlikely. They all do share a common ground."

You could run a test ground to one GROUND injector wire. Since it is common ground, that should make it run if we are right. Make damn sure you ground the right wire before you fry the ECU.

also fuel injectors get there power from the fuel pump relay. is your fuel pump running at all? and then that gets its power from the starter relay post.

90xj06 said:

also fuel injectors get there power from the fuel pump relay. is your fuel pump running at all? and then that gets its power from the starter relay post.

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Not on a Renix Jeep they don't. The power to the injectors is +DC pulse from the ECU. The fuel pump power comes from the battery through different paths, one for the run spot with engine not running yet (A timed primer) one for cranking, and one for running that goes through a ballast resistor. Re-read the posts, he has fuel and proper pressure and the noid light test showed no pulse (bad ground).

i only say this because the 90 fsm lists pin c11 and d10 as injector feed it is an orange wire that feeds the fuel pump and the oxygen sensor.

cruiser54 said:

ECU injector feed runs to pins D10 and c11 at the ECU. That feed comes from terminal 87 of the fuel pump relay.

http://i1354.photobucket.com/albums/q690/cruiser54/Jeep Tech Photos/renixrelaycenter.jpg

Click to expand...

I assume you mean I should get continuity between 87 and D10 by saying this right?

So I tried a continuity check between the 87 terminal of the fuel pump relay socket (relay out) to the D10 and C11 terminals on the ECU and didn't get any contact. I tried backprobing the ECU connectors (ECU was still connected to wire harness) and maybe they weren't getting good contact that way so I planned on trying it again with the connector unplugged from the ECU and see if I still have no continuity tonight after work.

also check if pin 30 has battery voltage.