'86 MJ 2.5L ECM....good?

[SoCalManche]

2 minutes ago, eaglescout526 said:

Lol no worries. We will find it. We will just keep running down the diag list until we get somewhere.

Well I truly appreciate it, so thank you.

[Ωhm]

All RENIX systems need a heartbeat. Check CPS using a voltmeter set to VAC lowest range available. Disconnect CPS, connect DVOM across component side connector (polarity doesn't matter). Looking for ≈2.5vac while CRANKING the engine.

[SoCalManche]

2 hours ago, Ωhm said:

All RENIX systems need a heartbeat. Check CPS using a voltmeter set to VAC lowest range available. Disconnect CPS, connect DVOM across component side connector (polarity doesn't matter). Looking for ≈2.5vac while CRANKING the engine.

Are you meaning disconnect it from the flywheel?

[eaglescout526]

No, he means you can unplug the sensor from the harness and test for Volts AC while cranking. I think he wants to make sure the CPS is sending out the proper signal.

 

here's the 86 engine and fuel management diagram.

[SoCalManche]

I unplugged the CPS from the harness and tried both back-probing and directly sticking the leads into the plug of the harness. I got 0V when cranking. This is with the fuel pump relay in the socket.

[eaglescout526]

Well that's odd seeing how with the relay in you get spark and engine fires when pouring fuel down the throttle body. The volt meter is on the Volts AC setting right? This is the only component that requires the VAC setting.

[SoCalManche]

11 minutes ago, eaglescout526 said:

Well that's odd seeing how with the relay in you get spark and engine fires when pouring fuel down the throttle body. The volt meter is on the Volts AC setting right? This is the only component that requires the VAC setting.

Initially, you caught my mistake. I was on DCV because I didn't see Ohm say "vac." I switched it to ACV and same thing; 0V. 

[SoCalManche]

3 minutes ago, SoCalManche said:

Initially, you caught my mistake. I was on DCV because I didn't see Ohm say "vac." I switched it to ACV and same thing; 0V. 

Dumb question; am I supposed to check the CPS side? I have been checking the engine harness connector, not the unplugged CPS sensor. I checked the CPS and it showed .32V on crank.

[eaglescout526]

What kind of MJ rabbit hole have we plunged into? Hopefully this won't be like the one where the hood lamp wire was plugged into the coil, but this is confusing to say the least.

 

Yes check the CPS side. I think .3 is a good number. I know Ohm said 2.5VAC .

 

Ok here is tip No.7 from cruisers website:

"Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS itself as shown in Figure 2 as Connector A, crank the engine over. It won’t start with the CPS disconnected.

You should get a reading of .5 AC volts."

"If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from NAPA or the dealer."

.32VAC is getting on the low end for the CPS output.

[SoCalManche]

2 minutes ago, eaglescout526 said:

What kind of MJ rabbit hole have we plunged into? Hopefully this won't be like the one where the hood lamp wire was plugged into the coil, but this is confusing to say the least.

 

Yes check the CPS side. I think .3 is a good number. I know Ohm said 2.5VAC .

 

Ok here is tip No.7 from cruisers website:

"Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS itself as shown in Figure 2 as Connector A, crank the engine over. It won’t start with the CPS disconnected.

You should get a reading of .5 AC volts."

"If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from NAPA or the dealer."

.32VAC is getting on the low end for the CPS output.

So should I buy a new CPS? Or would the low voltage be a byproduct of the resistance in my grounds?

[eaglescout526]

Me, I wouldn't rush out and get one just yet. We know the ECU will receive the voltage signal and tell the coil to spark which we can confirm by pouring fuel down the TB. So the CPS is not the entirety of the issue. We need to figure out why the pump won't turn on for one second and during crank/run. Has the pump been confirmed good before?  

[SoCalManche]

Define confirmation that it's good? I did a bench test on it via direct battery hook up, plus jumpering the relay circuit engages the pump too. I initially bought a new pump when the issue first started, and hooking it up showed the same symptoms as the other pump.

[eaglescout526]

Good as in the pump turns on and runs. But you say you don't hear it for that one second with and without relay correct?

[SoCalManche]

1 minute ago, eaglescout526 said:

Good as in the pump turns on and runs. But you say you don't hear it for that one second with and without relay correct?

As far as the way it is suppose to operate when you turn the key to ON, no it does not prime. However, when you throw a jumper wire in the relay socket, it will continuously pump until you pull said wire.

[Ωhm]

Sorry for the confusion. Yes CPS installed using the CPS connector.

Thanks for the correction. 0.5vac, not 2.5vac.

 

One more checkpoint here. Connect CPS back to harness. Disconnect ECU connector, using pins 11 & 28 on the ECU connector, check VAC again while engine is CRANKING.

[SoCalManche]

5 minutes ago, Ωhm said:

Sorry for the confusion. Yes CPS installed using the CPS connector.

Thanks for the correction. 0.5vac, not 2.5vac.

 

One more checkpoint here. Connect CPS back to harness. Disconnect ECU connector, using pins 11 & 28 on the ECU connector, check VAC again while engine is CRANKING.

With CPS plugged back in, same reading shows for pins 11 & 28 that showed for the disconnected CPS = .32-.35VAC.

[Ωhm]

That's kinda low borderline, but should be enough for a heartbeat. Is your vehicle a manual trans?

[SoCalManche]

Just now, Ωhm said:

That's kinda low borderline, but should be enough for a heartbeat. Is your vehicle a manual trans?

Yes.

[Ωhm]

Clutch stuff sometimes gets on the tip of the CPS. Only way to check this is to yank it. Not a easy task. Maybe put on hold until other things have checked out.

[SoCalManche]

Just now, Ωhm said:

Clutch stuff sometimes gets on the tip of the CPS. Only way to check this is to yank it. Not a easy task. Maybe put on hold until other things have checked out.

I unbolted the CPS from the flywheel the other day and cleaned it off, including its mounting points, because I know the CPS is a rather vital component for START.

[Ωhm]

CPS seem good. I might be barking up the wrong tree.

[SoCalManche]

1 minute ago, Ωhm said:

CPS seem good. I might be barking up the wrong tree.

I don't think any tree is wrong to bark up at this point because this gremlin continues to allude just about anyone that has an idea to what it could be.

[eaglescout526]

Ok so here's a couple troubles from the TBI book

 

Engine starts but won't idle: Fuel pump inoperative or ignition system malfunction.

Check fuel pump. 

Check the ign system. Repair as necessary. Check the start signal after engaging the starter motor. Voltmeter from D1 pin4 to D1 Pin3 should indicate zero volts.

Repair harness as necessary. Check MAP sensor. Repair as necessary. 

 

Engine will not start:

Defective Wide Open Throttle swtich(you might have this if theres no pressure switch on any of your power steering lines.)

Low Bat voltage

Fuel supply low

Low fuel pressure

Fuel pump inoperative

Defective secondary ignition circuit

Primary ignition input to the ECU defective

No bat voltage applied to the injector(12V from one pin top chasis ground)

Injector Ohm resistance too high(less than 10 Ohms)

ECU is not switching the injector

Leaking injector

No start signal voltage

ISA motor plunger not extended

Coolant temp sensor inoperative.

 

These are the possible causes the book lists. 

[SoCalManche]

5 minutes ago, eaglescout526 said:

Ok so here's a couple troubles from the TBI book

 

Engine starts but won't idle: Fuel pump inoperative or ignition system malfunction.

Check fuel pump. 

Check the ign system. Repair as necessary. Check the start signal after engaging the starter motor. Voltmeter from D1 pin4 to D1 Pin3 should indicate zero volts.

Repair harness as necessary. Check MAP sensor. Repair as necessary. 

 

Engine will not start:

Defective Wide Open Throttle swtich(you might have this if theres no pressure switch on any of your power steering lines.)

Low Bat voltage

Fuel supply low

Low fuel pressure

Fuel pump inoperative

Defective secondary ignition circuit

Primary ignition input to the ECU defective

No bat voltage applied to the injector(12V from one pin top chasis ground)

Injector Ohm resistance too high(less than 10 Ohms)

ECU is not switching the injector

Leaking injector

No start signal voltage

ISA motor plunger not extended

Coolant temp sensor inoperative.

 

These are the possible causes the book lists. 

So definitely not low bat voltage; pushing 12.5 and it's brand new.

I have plenty of fuel, it just won't push through.

 

Is there something, besides the grounds at the dipstick tube, that connects the fuel injector with the fuel pump? I still need to go get a test light, which I will do, but I just feel like the injector is also not properly working. But I believe it also needs to build proper pressure before it sprays? Or how does that work exactly?

 

[SoCalManche]

Also, for the ignition test, is it VDC or VAC? And do I record the reading during crank or after crank stops?