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Renix no spark after blown radiator hose - Crowd Source Diagnosis

88trailcrawler

88trailcrawler

NAXJA Forum User
Location
OC SoCal
I am in research and testing mode. Thought I'd drop this here for some ideas.

1988 4.0 auto. Has been running pretty good lately. Blew an upper radiator hose on the last leg of a road trip. No issues during the trip. Pulled over, changed the hose, refilled coolant. Started right up, idled a bit low but was running. Went for a test run and it shut off within about a block then would crank but not start. Towed it home.

Oil and coolant look good. Would not fire with starter fluid and there is fuel at the shrader valve. Wiggles, unplugged and replugged MAP CPS ant TPS. No obvious damage. Pulled a plug, looks clean and confirmed no spark.

Coolant temp sensor (lower one in block on driver side) crumbled in my hand, but I don't think that would stop spark. All others appear secure and intact. None are very old.

I am going out to poke around - please drop ideas or links as I'll be checking back until I get it resolved.
 
Well, first, fuel at the test port is not a good indicator of proper fuel pressure. But doesn't sound like a fuel problem.

Did you overheat before you pulled over?

Check your ign coil and connections. Take your distributor cap off and check inside.

I have an '88 4.0 Auto too. If you need some pics or measurements, let me know.
 
I can check fuel pressure later. I have confirmed no spark by laying a connected spark plug on the aluminum valve cover with no spark at cranking.

Checked, cleaned, wiggled, cleaned again, unplugged and replugged MAP, TPS and CPS several times. Same with 2 connectors at the coil and the nearby relays for good measure. All appear to be in order and uneffected by the underhood coolant steam bath.

The only damaged thing I see is the lower block tempuature sensor. My understanding is that the tempuature sensor will NOT affect spark and that the ONLY sensors that will create a no spark are the MAP, TPS and CPS.

I can order these and swap them out (CPS is a bitch) but I always thought these things got kinda finicky before death, which is not my senario.

Going to research how to test the coil pack.
 
Not sure if the CTS is needed to start on Renix. I think it is an issue for newer rigs, but not sure.

But no spark is usually the CPS, Ignition coil or ICModule under the coil. Coolant is highly conductive to electricity and when dried up still attracts moisture from the air and can cause HV to leak to ground. I would check the Dist Cap and rotor, the HV Coil, ICM, Spark plug wires, CPS connectors, and the alternator and I would wash them with distilled water (grocery stores stock it) and or Trichlorethylene based brake cleaner (non flammable plastic and paint safe).
 
TPS is not needed on Renix to start the engine. I use to start mine in my idle tests with the TPS disconnected on a fresh start.

I do not think the MAP is needed either. O2 is not needed either. Forgot the relays, it would be good to clean them and the wiring to them/connections and wiring to remove any coolant remains.

88trailcrawler said:
I can check fuel pressure later. I have confirmed no spark by laying a connected spark plug on the aluminum valve cover with no spark at cranking.

Checked, cleaned, wiggled, cleaned again, unplugged and replugged MAP, TPS and CPS several times. Same with 2 connectors at the coil and the nearby relays for good measure. All appear to be in order and uneffected by the underhood coolant steam bath.

The only damaged thing I see is the lower block tempuature sensor. My understanding is that the tempuature sensor will NOT affect spark and that the ONLY sensors that will create a no spark are the MAP, TPS and CPS.

I can order these and swap them out (CPS is a bitch) but I always thought these things got kinda finicky before death, which is not my senario.

Going to research how to test the coil pack.
Click to expand...
 
Well I made no progress.

Disconnected and cleaned all things mentioned. Simply getting no spark.

Don't know my next step other than throwing parts at it. I really don't think it's CPS because it's not very old, appears to be unaffected by the hose burst and it seems kind of too coincidental.

In need of a Renix guru.
 
Renix: The cranking voltage at the battery posts while cranking must be at least 10.0 volts for the ECU to work and fire the coil, test it.

The CPS must be putting out at least 0.50 Volts while cranking or a no spark condition will be very common. At about 0.35 volts on the CPS it will never start.

There are some old posts (Threads) by 8Mud and me here (OEM forum) in chats with me about an old no start problem I had (and others), that has test data for the ICM wire inputs from the harness to the ICM you can test next, to see if the ICM/Coil is getting the right data. If it is, you have a bad Primary spark wire to the distributor, or a bad HV coil or a Bad ICM. My last encounter at that stage was a bad ICM, I could see the burned/overheated are on the internal ICM circuit board. The black potting material that covers and waterproofs the circuit was melted/fried.
 
88trailcrawler said:
Well I made no progress.

Disconnected and cleaned all things mentioned. Simply getting no spark.

Don't know my next step other than throwing parts at it. I really don't think it's CPS because it's not very old, appears to be unaffected by the hose burst and it seems kind of too coincidental.

In need of a Renix guru.
Click to expand...

Was the new CPS aftermarket? And did you modify the bolt holes in to move it closer to the flex-plate teeth to up the voltage output yet??? My new ones only put out .35 volts, had to do the 5-90/Cruiser54 Jeep factory mod to get the higher signal voltage to get rid of one my no spark problems.
 
Thanks Mike.

That's my plan, to work backwards from the spark plugs (no spark), then coil output (can that be tested with a spark plug?) then ICM input. Those are all nice and easy to reach.

I do need to read up on CPS testing. I wasn't able to get a voltage read during cranking - not 100% sure exactly how to test that (sensor pig tail? Plug at harness? Or while connected?)

Also wondering about ways to jump power to the coil or ICM to confirm distributor, plugs and wires are all good???
 
I'm thinking what happened is akin to giving your motor an unexpected bath driving through a big puddle.

First thing I'd check is the high voltage cable boots (spark plug.coil) etc. Spark may be finding it's way to ground before it reaches the plugs.

Second is open up the distributor, make sure the insides are clean. Think about what may be under the cam position sensor mounting plate.

Check voltage at the larger yellow wire going to the ignition module. Then do a voltage test at the coil test point. Both should have voltage with the key in the run position. Typically a volt or two lower than battery voltage, line loss.

Hot water is one of the few things that will successfully clean coolant off. Hot water and weak suds is even better. Coolant is like Honey or Coca Cola and sticky.

Like Mike mentioned coolant is actually worse than water, it conducts better and can cause serious shorts where plain water might not be a major issue.

I've fried a coolant soaked alternator before. Where plain old very hot water does little to no lasting damage.

If your high voltage wires and ignition circuit are OK, it is likely a sensor issue. Whether it is a connector issue or the sensor itself is anybodies guess. A coolant soaked connector can short a sensor feed.

Hot water is your friend when rinsing off coolant, brake cleaner, WD40 etc. not so much.

I use very hot water in a garden watering can in a pinch to rinse off the majority of the stuff.
 
88trailcrawler said:
Thanks Mike.

That's my plan, to work backwards from the spark plugs (no spark), then coil output (can that be tested with a spark plug?) then ICM input. Those are all nice and easy to reach.

I do need to read up on CPS testing. I wasn't able to get a voltage read during cranking - not 100% sure exactly how to test that (sensor pig tail? Plug at harness? Or while connected?)

Also wondering about ways to jump power to the coil or ICM to confirm distributor, plugs and wires are all good???
Click to expand...

Test the CPS cranking voltage with the CPS disconnected from the harness probing the 2 connectors on the CPS pigtail. May need to use the AC volts scale, I forget, but use the low range so you can read it. It puts out a pulsed DC signal.

I thought you had checked for spark already at a plug wire?

Coil can be tested with the primary plug wire (from the coil the dizzy cap) and use a spark plug yes.

No way to jump the ICM/Coil, it needs a trigger signal from the ECU to trigger the ICM to fire the coil.
 
I always use the brake cleaner solvent (chlorinated one) to dry out parts after using the water, on parts like a Dizzy cap on the inside, as pure water will short circuit a HV spark as I recall due to the high voltage and especially around sensors and their connectors.

Nice post!!!

8Mud said:
I'm thinking what happened is akin to giving your motor an unexpected bath driving through a big puddle.

First thing I'd check is the high voltage cable boots (spark plug.coil) etc. Spark may be finding it's way to ground before it reaches the plugs.

Second is open up the distributor, make sure the insides are clean. Think about what may be under the cam position sensor mounting plate.

Check voltage at the larger yellow wire going to the ignition module. Then do a voltage test at the coil test point. Both should have voltage with the key in the run position. Typically a volt or two lower than battery voltage, line loss.

Hot water is one of the few things that will successfully clean coolant off. Hot water and weak suds is even better. Coolant is like Honey or Coca Cola and sticky.

Like Mike mentioned coolant is actually worse than water, it conducts better and can cause serious shorts where plain water might not be a major issue.

I've fried a coolant soaked alternator before. Where plain old very hot water does little to no lasting damage.

If your high voltage wires and ignition circuit are OK, it is likely a sensor issue. Whether it is a connector issue or the sensor itself is anybodies guess. A coolant soaked connector can short a sensor feed.

Hot water is your friend when rinsing off coolant, brake cleaner, WD40 etc. not so much.

I use very hot water in a garden watering can in a pinch to rinse off the majority of the stuff.
Click to expand...
 
Ecomike said:
I always use the brake cleaner solvent (chlorinated one) to dry out parts after using the water, on parts like a Dizzy cap on the inside, as pure water will short circuit a HV spark as I recall due to the high voltage and especially around sensors and their connectors.

Nice post!!!
Click to expand...

The thing about very hot water is it evaporates fast. Compressed air will help things along some. A hair drier will do in a pinch :) just don't let your wife see you.
 
One quick check you can do is to turn the key from off to run and listen for fuel rail prime. The fuel pump will run for a second or three.

This tells you the essential fusible links are likely still good.
 
X2 on cleaning out the inside of the distributor cap.
 
X2 on checking spark from the coil. Weird things happen. After changing out the water pump and running the XJ (95) for a couple 30 second periods to verify belt tension it wouldn't start after that. It turned out that the coil was dead. Go figure. It never got bumped, never got water anywhere near it. Definitely a WTF moment if there ever was one. Kind of like back in the day when I owned a couple of Triumph sports cars.


BTW old man, "they" know my name.
 
Some test data from this morning.

Battery: 12.55v and 10.96v at crank. A little weak, but should be sufficient.

CPS: only getting .18v while cranking on the ACV setting.

ICM: A to ground 10.4v cranking
ICM: B to ground <.5 ohms.
ICM: seperate yellow wire. 6-7v cranking.

Confirmed no spark coming out of the coil with an adjustable ignition testing tool. (Eliminated distributor/wires/plugs for now).

I guess that data indicates a CPS issue. Still hard to believe unless there is some logical contributing factor that connects that to the hose blow out (either before or after).

Big question for me is how to CONFIRM that the coil and ICM are good. Given the proximity to the hose blow out these make the most sense to me. Plus I am dreading trying to reach that damn CPS.
 
I can hear the pump prime. Haven't put a pressure gauge on it, but all indicators suggest fuel delivery. Plus I've confirmed no spark at the plugs and coil.

Do you know how to confirm ICM and Coil?

8Mud said:
One quick check you can do is to turn the key from off to run and listen for fuel rail prime. The fuel pump will run for a second or three.

This tells you the essential fusible links are likely still good.
Click to expand...
 
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