Died while driving, won't start

[CO MJ]

I've been having a misfire problem while taking sharp slow turns and sometimes while going uphill, but it's always gone away quickly, sometimes letting off or giving more throttle will fix it. Today it started on the freeway and while playing with the throttle to get it to go away, the engine stopped running, coasted to a side street, and now it will turn over but it will not fire.

 

I checked spark from the coil and from the distributor with a light and I am getting spark. I didn't have anything to measure fuel pressure, but it came out of the valve on the rail pretty good.

 

I am going to go back in the morning after things have cooled off and see if it'll start. I am suspicious of the CPS. Maybe bring a can of starting fluid and see if it'll hit. Something to check timing (chain potentially slipped?) 

 

Any other tricks I can try before I pay someone to tow me a whopping two miles?

[eaglescout526]

TPS can be known to do funny things when it is heat soaked but don’t count on it. Multimeter will tell you if the CPS is good in the AC position on the meter. 

[CO MJ]

20 hours ago, eaglescout526 said:

TPS can be known to do funny things when it is heat soaked but don’t count on it. Multimeter will tell you if the CPS is good in the AC position on the meter. 

TPS wouldn't cause a no start though right?


Update; fuel pressure is great, tested the CPS again and got a strong .5 AC, replaced with new anyways and same result.

I can't find my test light, but I'm not reading a signal on the injectors with my meter. Possibly my meter is just too slow to see it, but I'm suspicious the injectors are not firing.

Based on the wiring, I would think if the ECU is telling the ignition module to fire, it's probably also telling the injectors to fire, and the signal isn't making it. I'll check the ECU to make sure it's powered on, and check continuity to the injectors.

 

Is anyone aware of any other sensor/input/whatever that would prevent the ECU from sending signal to the injectors?

[CO MJ]

Update

ECU has power from battery and ignition, continuity to injectors, but I am not seeing a signal to the injectors at the injector or straight off the ECU pin.

[eaglescout526]

Noid light will help tell if the injector circuit is working. A failed injector would cause a no start. 

[CO MJ]

55 minutes ago, eaglescout526 said:

Noid light will help tell if the injector circuit is working. A failed injector would cause a no start. 

How does the ECU know if the injector is bad? I would think even if I unplugged them all I should still see the signal on the wires

[eaglescout526]

It wouldn’t know if it’s bad at all. It just runs the ROM and it pulses the injector. You won’t see a signal on a VOM, hence why noid lights exist for this reason. 

[gogmorgo]

Injection timing signal is controlled the sync sensor in the distributor. Sometimes called the cam position sensor. I've had a bad signal cause a no-start in my HO, not sure about Renix. In my case had radial play in the distributor shaft cause problems.

I think it's highly unlikely all six injectors would fail at once. It would at least splutter if fuel is making it out of some of the injectors. Probably run with only four injectors, maybe even three. But a noid light is definitely the way to check for signal.

[CO MJ]

On 8/4/2023 at 6:02 PM, eaglescout526 said:

It wouldn’t know if it’s bad at all. It just runs the ROM and it pulses the injector. You won’t see a signal on a VOM, hence why noid lights exist for this reason. 

 

8 minutes ago, gogmorgo said:

Injection timing signal is controlled the sync sensor in the distributor. Sometimes called the cam position sensor. I've had a bad signal cause a no-start in my HO, not sure about Renix. In my case had radial play in the distributor shaft cause problems.

I think it's highly unlikely all six injectors would fail at once. It would at least splutter if fuel is making it out of some of the injectors. Probably run with only four injectors, maybe even three. But a noid light is definitely the way to check for signal.

 

Looks like no signal to the injectors. Would a bad sync sensor prevent the ECU from trying to fire the injectors at all, or just throw off the timing? I think that is the only sensor I haven't verified recently. I think next I will check all the ECU power and ground connections to make sure it's running, it was pretty hot to the touch I noticed which makes me thing maybe the ECU is fried

[CO MJ]

Checked all sensors again, everything seems to be behaving as expected, still no signal to the injectors. I think next step is to check all inputs at the ECU connectors and hope something is missing, and if everything is there, and ECU has all the expected power and grounds, then I must assume the ECU is shot?

I also got the advice to check the resistance of the injectors to see if any were shorted internally and they all read good. 

[CO MJ]

I have now checked everything I know how to check at the ECU connector as well.

Neutral safety switch pin is grounded

Injector wires have appropriate resistance

Fuel pump relay is energized and injector feed pins on the ECU are receiving power

CPS reads .5v

Latch relay has power

Start signal from the starter relay has power

TPS reads the correct range

Map sensor reads ~5v and drops with vacuum applied

Battery pin has power

Grounds all have continuity to the negative battery terminal

It seems to me like the ECU has everything it needs, but still no signal to the injectors. I believe the ECU is on because it does output a signal to the latch relay, fuel pump, 5v to some sensors, oxygen heater relay, etc. but I don't see any definitive test to check if the ECU is working. No blown fuses, but I don't think there's any that could be bad with these symptoms. Unless the portion of the ECU that controls the injectors has melted a transistor or something, I'm absolutely stumped. None of the yards around me have a renix jeep, and I'm hesitant to buy one online just to find out it doesn't work either and no ability to return it.

 

Can anyone confirm which sensors the ECU absolutely requires to power the injectors? I believe the sync sensor and maybe the egr and  temp sensors will not prevent the ECU from starting the engine, but the map and cps sensors will, but I can't find any confirmation.

 

Also if anyone has a renix code reader in texas, please DM :)

[Ωhm]

2 hours ago, CO MJ said:

Latch relay has power

 

Just what does this mean?

 

I've now learned that B+Latch Relay is more than just for resetting the IDLE motor (4.0L) at ENGINE OFF, it can also cause a ENGING CRANKS, NO START condition.

 

@GrandBoost98

@Glenn Bint

[CO MJ]

Just now, Ωhm said:

 

Just what does this mean?

 

I've now learned that B+Latch Relay is more than just for resetting the IDLE motor (4.0L) at ENGINE OFF, it can also cause a ENGING CRANKS, NO START condition.

 

@GrandBoost98

@Glenn Bint

ECU is sending a signal to the latch relay coil, and battery voltage is coming through the relay to the ECU as expected, and the signal to the relay goes away a few seconds after turning the ignition off as expected

[Ωhm]

That sound good, acting as designed. So, shooting starter fluid down the throat and cranking engine still give nothing? No kicking. No bucking.

[CO MJ]

49 minutes ago, Ωhm said:

That sound good, acting as designed. So, shooting starter fluid down the throat and cranking engine still give nothing? No kicking. No bucking.

It will fire on starter fluid, it has spark on all cylinders. Something is either causing the ECU not to fire the injectors, or the entire ECU or the portion that modulates the injectors is shot. The only things I see that explicitly will cause the ECU not to fire the injectors in the fuel injection manual is no cps signal, no throttle at high rpm (so heavy deceleration, but my throttle signal is fine and I'm not sure this condition applies the the ECU crank mode), 

[Ωhm]

KEY OFF. Check for continuity between:

 

∙D1_3 and D2_7

∙D1_3 and Battery Negative terminal

∙D2_7 and Battery Negative terminal

 

Looking for continuity. (≈0Ω)

 

 

[CO MJ]

1 hour ago, Ωhm said:

KEY OFF. Check for continuity between:

 

∙D1_3 and D2_7

∙D1_3 and Battery Negative terminal

∙D2_7 and Battery Negative terminal

 

Looking for continuity. (≈0Ω)

 

 

 

Diagnostic connectors checked out too. Opened up the ECU, nothing obviously burnt, but the big heatsink with all the power transistors was a little hotter than I would have expected, will try to see if I can find any info on the ECU internals tomorrow.

I think I'm going to go ahead and order a replacement ECU as well. Hopefully I don't fry it too :|

[Ωhm]

FYI stuff. Hope it helps.

 

Bosch PFI Noid Light OTC 7188

 

Found this some time ago and YES injector drivers get HOT, that why they mount them on HEAT SINKS.

 

[CO MJ]

13 minutes ago, Ωhm said:

FYI stuff. Hope it helps.

 

Bosch PFI Noid Light OTC 7188

 

Found this some time ago and YES injector drivers get HOT, that why they mount them on HEAT SINKS.

 

Fantastic!

Looks like it is the 5v regulator that is getting the hottest, I didnt notice any of the ones labeled as injectors heating at all, but the one labeled in series with injectors seems suspicious to me. I can't imagine all 6 injector transistors failing at once but if that one effects them all, maybe that's the culprit

[CO MJ]

Put in a new map sensor just for giggles this morning, no dice. Also tried manually pulling a vacuum on the sensor in case maybe the outlet on the throttle body was clogged, still nothing. Tried disconnecting the TPU in case the ecu was maybe detecting WOP and looking for a higher rpm from the CPS, still nothing.

 

Going to try to put together nicks engine monitor and see if I can get some kind of data out of the ECU. Maybe look more into the injector driver and see if that one transistor is blown. New ECU should be in tomorrow as well.

[CO MJ]

I ended up pulling the engine control harness to remove the spaghetti mess the PO created while converting to an automatic transmission. Repinned a few things on a junkyard harness, still nothing. Checked all the ECU pins again, all looks as expected. Swapped the ECU with a reman unit, fired right up. 

 

Anything I should be looking out for that may have fried the original ECU? I checked all the pins at the ECU connector for shorts to ground, and nothing looked like it was getting voltage that shouldn't. All injectors have good resistance.

[Ωhm]

9 minutes ago, CO MJ said:

Swapped the ECU with a reman unit, fired right up.

 

 

10 minutes ago, CO MJ said:

Anything I should be looking out for that may have fried the original ECU?

Spaghetti wiring mess. 

 

[CO MJ]

34 minutes ago, Ωhm said:

 

 

Spaghetti wiring mess. 

 

Removed! Looks like the PO Tried splicing in the TCU bits of another harness into the original manual harness instead of replacing it with the correct harness for whatever reason. Just need to go back and wire up the c115 connector to the dash (fingers crossed the manual came with that connector and I don't have to make my own harness)