eaglescout526

Looking at the diagram I think you are just looking for to see if there is a break in the line between T6 and relay terminal 85. So once you get your probes in place, that's when you would do the key on test and see what the volt meter shows for voltage if any voltage goes to the relay.

So see where the relay is in the third pic of the second half? Looks like 86 jumps to 85 and goes into T6. I just realized I screwed up the pic alignment but where the relay goes down to the ECU in the diagram, it shows the EGR but it really goes to the area of the ECU diagram marked fuel pump relay which is T6.

I think that's why the book says to test T6 and the relay to make sure there is continuity there. T6 has the power to trigger the relay for that one second and then stop. While the relay itself waits for power from the start up procedure to run the pump. I only saw one associated with the fuel pump relay and a couple other things. Below is the top image split into four to see the words better. First half. Second half. This is from the PDF electrical manual. Hopefully this will help give an idea as to what we are looking at.

One would send power to the fuel pump and the other is the fuel gauge wire. I think the fuel gauge was C. Well I did some looking at the electrical book and saw a couple things. First I saw is there is a fusible link tied to the fuel relay harness. Second the connectors would be at the tank(1), second would probably go into the cab behind the kick panel then probably into the engine bay wiring harness that routes back to the ECU. Well I am learning more about the diagrams but ill admit the last two after the kick panel are a shot in the dark.

Yes and no. I am not sure if any one of the fusible links is even apart of the fuel pump harness, but i was just thinking about the contact tabs and such on the starter relay as those can corrode too and cause resistance or loss of power. Yes you can. No, I was thinking more using the connectors as breaks in the harness. Rather than getting really long leads and putting one in the relay harness and the other at the pump itself, I was thinking of using the connectors as testing sections so that way you aren't trying to dig into the entire harness when hunting down the problem. So that way when testing from one connector to the next and suddenly an open loop comes up in one section between two connectors, the problem could lie there. Ohm will probably correct my thinking if I'm wrong.

Lol fair enough. I just typed what the book has. But I am not great at explaining things to others in simple formalities but here goes. So when you turn the key, the pump comes on and primes. Common knowledge with Renix. Since its not coming on there probably an open circuit somewhere in the fuel harness between the pump itself, the ground and the relay to the ECU. Or possible corrosion of a contact or wire. So you already jumped the relay harness and still got nothing which means there is something going on in the harness. Which makes me wonder the condition of the starter relay connectors.(not entirely related but apart of the start up procedure per the ECU) Since the pump doesn't operate we can't check for voltage. Well you still could to see if there is any power at the relay contacts. Checking the continuity of the circuit to see if there is any power between the two ends. As for checking continuity between the pump and the relay, if I had the wiring diagram for the pump to relay, they probably mean for you to check each connection so like the fuel pump to its first harness connector, then from that connector to the next one until you reach the fault or relay contact. Then checking the ground circuit would be the same deal, making sure there are no breaks or corrosion between the connector and the ground behind the lamp. I think I explained it well enough. If not let me know.

That is correct! I forgot all about that. 80's to 90's GM coolant bottle caps do indeed fit. I know a guy who has a Fierro and he had that coolant cap and I tested it and sure enough it fit as it should.

Ok so the component diag section states this Fuel pump will not operate for one second with the ignition switch on Possible Cause: Open circuit or fuel pump ballast resistor defective, which Jeep didn't get the later till 87 from the factory. So you have already done the first part, connect a jumper wire across the fuel pump relay If the pump operates, check for battery voltage at the relay. Check the continuity betwenn the relay and Pin 6 at the ECU. Repair the wire harness as necessary. Replace fuel pump relay. Test ECU with MS-1700. Test for continuity between the fuel pump and relay contacts(long enough leads much?) Check the pump ground circuit. Repair the harness as necessary.

Well its doing something. But we couldn't get a clear picture on why the ground has an open circuit.

RPMs fluttering would be a possible MAP sensor issue or something with the EGR and its solenoid.

Ok so I'm sitting here watching the X-files again and in S1E10 theres an MJ with a camper shell parked in the motel parking lot. That one isn't recorded in the link above.

Hmmm. Something is funky with the wiring and I'm not sure what. Would an 86 have two of those five pin connectors by the relay center?

My block has a standard hex head. That’s why I find it odd. We will get this figured out. Know of any rodents that could’ve gotten in?

Oh ok I see what you’re saying now. Soldering them at the crimps will help. Nope none enter my mind unless changing where the sensors ground at but I’m sure somebody else would speak before telling you to change the ground for the sensors. Odd that you have a torx bolt for the dipstick.

I have no idea what the soldering would do. Probably would make it more challenging to replace the rings if they disintegrate.

here's a couple tests from the book Injector resistance is too high, Ohmmeter should indicate less than 10 Ohms. ECU is not switching the injector. Remove injector harness connector. Connect a test lamp to the connector. Engage starter the starter motor. The lamp should pulse dimly. These are the only tests I found for the injector.

Could be. You have verified that the pump does indeed work correct? Theres a few possible causes for engine not starting but most aren't the issue. But it seems fuel related as you said the engine fires when given fuel. But still that MAP circuit is concerning.

Huh interesting. So the MAP circuit and the fuel pump are affected. Hmmm let me see what the diag chart says.

Yes and if you did it right and according to the book O.L. indicates defective ground. Ok this is good, meaning the ECU isn't being fried by backfed 12V. So we can say there definitely is some sort of ground or wiring problem. So I know from goofing around the engine won't run without the MAP or the CPS(obviously the CPS). Theres something funky going on and you upgraded and cleaned the grounds per Cruisers tips. Did you by chance get the ground from the post to the alt bracket I believe? I know on my 88 the ground goes from the post to the alt bracket. And you have confirmed spark too right? Just engine won't run.

Yeah not like the 4.0L when I pulled an ECU for another member Lets do the last step and see what Ohm testing T17 and T2 gets. I want to ask, what kind of shape is the engine harness in in it entirety?

See if you can back probe the ECU connector. If you can I would plug the ECU back in and do some back probing. Oh wait never mind its a giant plastic plug that can't be back probed if I remember correctly.

That's fine, it will help for better grounding. Thinking to myself, you won't have the C101 cause its an 86 so no tar to clean out. Getting O.L. Ok I'm going to type verbatim what the books says. MAP Sensor test: Inspect the MAP sensor vacuum hose connections at the throttle body and sensor. Repair as necessary Test the MAP sensor output voltage at the MAP sensor connector terminal B(as marked on the sensor body) with the ignition on and the engine off Output voltage should be 4 - 5 volts. Note: The voltage should drop to 1.5 - 2.1 volts with a hot, neutral idle speed condition(not applicable cause you can't get the engine to run) Test ECU T33 for the same voltage described above to verify wire harness condition. Repair as necessary. Test the MAP sensor supply voltage at the sensor connector terminal C with the ignition ON. The voltage should be 5 volts(+or- 0.5V) Five volts should also be at T16 of the ECU wire harness connector. Repair or replace the wire harness as necessary. Test the ECU with diag tester MS-1700 if necessary.(Wish we could find one) Test the MAP sensor ground circuit at sensor connector terminal A and ECU connector T17. Repair the wire harness if necessary. Test the MAP sensor ground circuit at the ECU connector between T17 and T2 with an ohmmeter. If the Ohmmeter indicates an open circuit inspect for defective sensor ground connection on the flywheel/drive plate housing(bell house) near the starter. So the dipstick ground is what this is for us. Book covers three engines with the same TBI set up. If the ground connection is good, replace the ECU. If T17 has a short circuit to 12 volts correct this condition before replacing the ECU. So there's a little bit of resistance after all.

Youre doing it right. I just wanted to make sure that you have been testing with key on. I'm not sure how much of a diff the ECU unplugged or plugged in makes but it could help rule the ECU out. How does the dipstick ground look on the block? Clean and shiny? Most if not all the sensors ground out at that grounding point. Just for giggles ohm test the ground post to the engine ground strap on the fire wall and see if it will say O.L. I will admit it can be tricky to get good contact while back probing the connectors.

VDC DCV still DC voltage. Hmmm. This is interesting then. Try A to the Neg battery post and see what Ohms we get. We shouldn't get an open loop between A and T17 but we should be getting something at C+T16. Now we do have the key on engine off when testing right?

And you're using VDC right? Test Grounds by using Ohms, we don't need to see voltage on ground circuits just resistance and open circuits. Buuuuuuttttt if we see voltage on any of the grounds then we have a problem.