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'88 Xj (Renix) - Crank, No Start

R

RAVC1

NAXJA Forum User
Location
Michigan
This is a discussed topic on NAXJA but, I did not locate much useful for my current conditions. These are:

1 - Driving Xj yesterday and the 4.0L stopped. A cloud of smoke (white) rose up from the hood. I assumed this was unburnt fuel traveling backward in the induction system. Starter continued to crank but, no start.

2 - My prior experience with Renix Xj no starts is that these are due to: 1) bad MAP, 2) bad CTS (near lower left engine mount) and, 3) bad CPS. Presumably, this is just the list of primary reasons for a no start.

3 - Replaced MAP with a used unit. No change; crank but, no start.

4 - Had Xj towed home so at least it's inside.

5 - Verified no spark on Cyl3 this morning.

6 - Performed dynamic CPS test. Measured just under 0.5 VAC when cranking. I concluded CPS is likely to be okay.

7 - FSM contains no indication of how to measure primary & secondary coil resistance. Anyone?

8 - How do we troubleshoot the Ignition Command Module? Check I/O with meter?

9 - What about an ignition relay? The FSM is lacking in this regard too.

10 - Obviously, I cannot rule out the ECM either (at this stage).

Any help is appreciated (especially today...).

Rick
 
Start out by checking the MAP vacuum hose at the throttle body to see if it blew off during the backfire.

Check for fuel at the fuel rail (pressure test if you have a gauge, and do a fuel pressure leak down test). Pull the spark plugs and inspect them, dry them if they are wet with fuel.

Is there spark at primary HV wire before the distributor (ICM coil output wire)? That wire should read about 1000 ohms, end to end on an ohm meter, test it too.

Pull the cap on the distributor and see if it rotates when the you crank the engine.

Check for dirty, dust, oil or damage, HV tracks inside the cap or damaged rotor.

Check the sensor net work ground with an ohm meter, sensor to the negative battery post, needs to be under 1 ohm.

Then try again. If it does not start in 4-5 seconds, press and hold the gas peddle to the floor, WOT and crank again, in 7 second bursts (let the battery and starter rest in between), that tells the ECU to shut off the injectors, and lets the engine dry out if it is flooded. If it is flooding check the vacuum line on the fuel pressure regulator on the fuel rail for gas. If there is gas there, the FPR is leaking, and is bad.

Try all that first. If not spark at a good primary HV wire, then I will dig up the old notes here in the old posts.

Note the ECU, MAP and ICM and HV coil on Renix rarely go bad.
 
Ecomike,

Good thoughts. My responses are:

My backfire was non-existent; only evidence up out of the engine bay. Nothing out of the tailpipe, no sound. However, I will check the MAP hose at the throttle body.

I doubt I have a fuel problem as significant as your are getting at but, I do not know. I hear the fuel pump (as I always do at Key ON) and a few consecutive attempts to start the engine gives rise to the aroma of fuel. I do not have a fuel gauge at this time.

You refer to the ICM input. This must be the signal from the Renix. If I knew a known safe method to measure this with key on or cranking I would attempt this measurement. Your comments here seem to refer to more than one issue. All my wires (Magnecor), rotor, cap, plugs were new in the late summer/early fall.

Two years ago I cut 2"-3" of wire off each of the sensor grounds and soldered new terminals on them and cleaned the stud at the oil dipstick. However, I should assume rust has not returned due to our excessively salted roads.

Thanks for the thoughts.

Rick
 
Well I have read stories of early failures of most sensors and rotors and caps, a lot more recently, so never assume any thing, even about new parts. If the distributor is not new, I had one piss oil all over the inside of the cap and rotor one day, LOL, and no external signs yet, but it would not start. The lower shaft seal oring had failed to seal.

Sounds like you have gas, so be sure to check the FPR on the fuel rail, at the vacuum line, takes all of 15 seconds!!!! If there is any sign of gasoline in that vacuum line it is flooding the engine, bypassing the fuel injectors.

If there is spark at the output coil, there is no need to check the ICM inputs.
 
Last edited:
White smoke under the hood really sounds like steam. I would focus on this. Your explaination for what caused it does not sound right. Did it overheat at all? Where was the smoke coming from? Steam can condense inside the distributor and short the spark to ground, causing no start. Clean inside of distributor cap. Look for evidence of coolant leak.

Also check for burned/melted wires. They can sometimes cause white smoke. Check the CPS wire against the header.
 
old_man said:
White smoke under the hood really sounds like steam. I would focus on this. Your explaination for what caused it does not sound right. Did it overheat at all? Where was the smoke coming from? Steam can condense inside the distributor and short the spark to ground, causing no start. Clean inside of distributor cap. Look for evidence of coolant leak.

Also check for burned/melted wires. They can sometimes cause white smoke. Check the CPS wire against the header.
Click to expand...

Hmm, I was thinking a poof out the intake, smoke, all at once out the MAP sensor connection on the side of the throttle body (I have seen that before) Did not think of steam. I would think steam would be obvious afterwards?

Burned wires sounds possible, good idea, also the O2 sensor wires, I smoked that run of wires real good once on my 87!!!! The wires got attacked by the front drive shaft, then the Ex-manifold, and the 12 V heater wire went right to ground and smoke the insulation real good.
 
Last edited:
FPR tested fine - no fuel in its vacuum line.

No spark is the primary condition I need to address, no others until my '88 Xj starts. This remains true after working this afternoon. Here is the summary from my first session today:

Known good CPS WITH drivability issues (i.e., can only use this for troubleshooting before I try to determine what is wrong with it...). This CPS also features the highest AC voltage but, by few millivolts above the initial CPS. Effectively, a control for better 'initial' conditions.

B(+): present on ICM-A. FSM does state ECU pin 27 input to ICM is a 5 VDC square wave. My DMM can read this so I must check this evening.

Sensor ground good: < 200 mV (- battery terminal to sensor ground by dipstick).

Coil lead to valve cover/bolt: no coil output. With all of this combined does this state the ECM is the reason for my no spark? I have B+, my sensor ground is okay so this must be okay at ICM too.

Distributor was checked yesterday. Cap removed and no signs of carbon in view of its short life in the car. Rotor moves with crank. No oil, water or moisture under cap. Can the 'Sync Pulse' result in a no spark condition if it is absent? I have not checked the distributor pigtail yet.

If ECM 5 VDC is sound, I will be forced to replace the ICM/coil assembly. I have removed this from the car but, as with most of my other sets I can only remove one of the coil securing screws.

Thanks,

Rick
 
Last edited:
See post #2 for the ICM input test data:

http://www.naxja.org/forum/showthread.php?t=1050783&page=11

I do not understand the CPS info you are trying to describe. Can you explain better?

Be sure to read that entire thread linked above, as I fought with a brand new Renix CPS for weeks before I could prove it was defective, intermittent.
 
Last edited:
I am still with old_man on sourcing the smoke you mentioned as possibly burned wires? And IIRC 200 MV is about 10 times too high for the sensor grounds, should be more like <20 MV IRRC. Or <1.0 ohms with power off.

With engine running the CPS voltage should be several volts AC, 3-4 V or more IIRC, not just barely over .50 V AC.

If the dizzy sync is bad it will still try to start, it will eventually spark, but may spark the wrong cylinder.

Be sure to remove the HV coil from the ICM base, and clean the 2 E-contact pins and clips!!!
 
Last edited:
Ecomike,

This problematic CPS is new (Echlin...Champlain on the wire shroud?). After I removed the AW4 and installed the AX-15 (2010) the car bucked like a wild bronco horse on the test drive home. I would describe this as a possible loss of electrical power. A few seconds later everything was fine. This repeated 2-3 times in a sequence then the behavior vanished. Drove the Xj with this CPS for months and the same problem arose, wild bucking bronco but, more severe. This continued at several week intervals before I installed the original CPS from the AW4 no issues since with the exception of my current situation. This occurred less than 6 times in just over a year of using this CPS.

Power was off when I tested the sensor ground between (-)Batt and engine block.

I have not located much on the CPS AC signal. Your values below will help me tomorrow. I have never checked the AC signal before this as I've never experienced these problems before.

I will probably break or, grind off the head of the bolt I cannot remove from the ICM base so I can make progress by exchanging ICM/coil pairs in an ordered fashion.

The puff of white smoke I alluded to was sparse, small and located to the left of the hood center line when it emerged from the engine bay. At the moment I think the unburnt fuel being forced up and out the induction system is the best interpretation in view of how my Xj is behaving. I am too busy troubleshooting my lack of spark to get serious regarding other issues. All wires in the vicinity of the ICM/coil and relay center are fine. I even pulled on the fusible links some this afternoon too see if they were still sound (they appear to be). I have a known coolant leak but, this requires small additions of coolant every month if I keep after it. My dipstick is clean so no blown head gasket...at least not yet. However, this would not prevent an engine start.

I'll read the posts you referred me to momentarily. More study tonight and work tomorrow.

Thanks again.

Rick
 
Renix CPS Testing and Adjusting
　
　
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
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, 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.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out the upper mounting hole, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.

　
　
Revised 07-30-2012
 
Be advised that a plethora of critical signals travel through the c101 connector-


Renix Jeep C101 Connector Refreshing
　
The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of almost 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before.

Almost every critical signal between the engine sensors, injectors, ECU, and some to the TCU, travel this path through the C101 connector.
The C101 connector is located on the driver’s side firewall above and behind the brake booster. It is held together with a single bolt in it’s center. To get the connectors apart, simply remove the bolt and pull the halves apart. You will find the connector is packed with a black tar like substance which has hardened over time.
Take a pocket screwdriver or the like and scrape out all the tar crap you can. Follow up by spraying out both connector halves with brake cleaner and then swabbing out the remainder of the tar. Repeat this procedure until the tar is totally removed. This may require 3 or more repetitions. Wipe out the connectors after spraying with a soft cloth.
If you have a small pick or dental tool, tweak the female connectors on the one side so they grab the pins on the opposite side a bit tighter before bolting both halves back together.
　
Revised 07-17-2012
 
Something else to eliminate as an issue:

Renix Jeep ICU/Coil contact refreshing
　
　
The contacts between the coil and the ICU on your Renix Jeep can become corroded and loose causing a complete or intermittent no-start condition. I recommend the following procedure as a maintenance precaution to insure this is eliminated as a possible cause now and in the future.
The coil is attached to the ICU by two T20 Torx bolts. Remove these two bolts and lift the coil up off the ICU. You will see 2 pins and 2 sets of contacts. Clean both the pins and springy contact pieces with a good electronics cleaner.
Squeeze the springy contacts closer together with some needlenose pliers. Apply some dielectric grease to the contacts and bolt the coil back on to the ICU.
While you’re right there unplug the connectors from the ICU and inspect the pins in the harness connector. Make sure the pins are not retracted into the connector. Spray out the connector and the receptacle of the ICU with the same good electronics cleaner you used earlier. Apply dielectric grease to the connectors and plug them back in.
I feel this procedure should be performed at least once in the lifetime of a Renix Jeep.
　
Revised 11-29-2011
 
FWIW, I dissected the new CPS that finally proved to be bad, and near as I could tell the problem was poor electrical contact between the angel fine hair of the magnetic coil wire, and the external sensor electrical contact wire, inside the sensor.

 
RAVC1 said:
Ecomike,


Power was off when I tested the sensor ground between (-)Batt and engine block.
Click to expand...

If you had 200 MV on the ground wire with power off, you have a real ground problem!!
 
Ecomike - The value you placed in your 5th post indicated <1.0 V w/power off for sensor ground. Now you have left me confused. Clearly, I can resolve this tomorrow.

The issues cruiser54 made regarding C101 are known to me and I confess I have never had this connector apart. I will state I prefer cutting 2"-3" off each side of C101 and soldering patches. It actually seems less time consuming too.

Yes, my CPS clearance holes will get larger tomorrow. Perhaps the upper one first or solo as one of my 'better' CPS features witness marks!
 
RAVC1 said:
Ecomike - The value you placed in your 5th post indicated <1.0 V w/power off for sensor ground. Now you have left me confused. Clearly, I can resolve this tomorrow.

The issues cruiser54 made regarding C101 are known to me and I confess I have never had this connector apart. I will state I prefer cutting 2"-3" off each side of C101 and soldering patches. It actually seems less time consuming too.

Yes, my CPS clearance holes will get larger tomorrow. Perhaps the upper one first or solo as one of my 'better' CPS features witness marks!
Click to expand...

Bypassing the C101 by SOLDERING the wires is a good idea. Below are a few things which should simplify your understanding and testing of your Renix system.
Renix CPS Testing and Adjusting
　
　
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
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, 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.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out the upper mounting hole, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.

　
　
Revised 07-30-2012
Cruiser’s Renix Sensor Ground Test
　
This sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate.
Set your meter to measure Ohms. Be sure the key is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.
You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.
Revised 06/12/2012
 
RAVC1 said:
Ecomike - The value you placed in your 5th post indicated <1.0 V w/power off for sensor ground. Now you have left me confused. Clearly, I can resolve this tomorrow.

The issues cruiser54 made regarding C101 are known to me and I confess I have never had this connector apart. I will state I prefer cutting 2"-3" off each side of C101 and soldering patches. It actually seems less time consuming too.

Yes, my CPS clearance holes will get larger tomorrow. Perhaps the upper one first or solo as one of my 'better' CPS features witness marks!
Click to expand...


No I indicated < 1.0 OHM, not < 1.0 V, with the engine and ignition switch off.
 
My B(-)/Sensor ground = 200 mOhms maximum with key off. I removed the bolt, all ring terminals and checked that the stud was shiny clean. None of these connections held soil of any type as a result of my refreshing them in 2010. The sensor grounds appear sound.

I filed the clearance holes in my initial CPS mounting bracket to the outer point of the witness marks of the star washer pattern. I pressed on the black body of the CPS as I tightened the shoulder bolts. Now I have ~3.3 VAC when cranking!

All good news but, still no engine start or spark.

I separated each ICM/coil pair this morning and all primary measurements are 0.8-1.0 Ohms. All my secondary coil measurements are 6.3 - 6.7 kOhm maximum. If anything is here it may be the secondary coil but, in much of the reading I have done in the past few days I do not see this as an obvious no start issue.

What next? Should I monitor ICM tach signal to assess ICM? Does anyone know if this can also indicate ICM sparking functions are okay? It would seem odd to me that tach indicates ICM output but, we do not have schematics for the ICM.

From what I just observed it seems like the Renix needs to be replaced or I need to work with C101.

Rick
 
I forgot to mention that I surveyed all of the engine area wiring. Nothing visibly burned or any loss of insulation that I found.
 
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