Doesn't Want To Start

[MJCARENA]

Hello my 1988 4.0 auto Comanche is being stubborn. Started her up and pulled it out of the garage so I could clean up the garage. Ran a little rough, I just figured it was cold. At the end of the day I go to pull it back in and it just cranks. No start and doesn't sound like it wants to. I checked the fuel pressure and have 32 psi. Checked for spark and have it at the coil and at the plugs. The exhaust smells like gas so I assumed it was flooded. Pulled the plugs out and they looked good, not wet or fouled, Put a new set in just to be sure. Still just cranks. Listened to the injectors while cranking and can hear them working. I have eliminated the 101 connector by passing it about 5 months ago. Redid my grounds and did the ground upgrade including soldering the splices then also. A fellow worker suggested to try starting fluid to see if it will try to run. I did this and it starts and runs fine, but when I turn it off it will not start again without starting fluid.Very strange. The fuel pressure is 32 psi when it is running and 40 when I pull the vaccum line of the regulator. So I assume my pump is good, Can also hear the pump run when you turn the key on. Any advice would be greatly welcomed.

[cruiser54]

So it runs and DRIVES fine after using starting fluid to get it going?

[boman40]

Change the fuel filter and check fuel pressure again, if the same as before, change the fuel regulator and check your air filter.

[MJCARENA]

So it runs and DRIVES fine after using starting fluid to get it going?

 

I have not driven it. Just idle and rev the engine in park and idle in gear. Will take it out for a drive tomorrow.

[MJ_Milam]

here is some info from alldata you can try and see if it helps

1. Connect a 0-689 kPa (0-100 psi) pressure gauge to the the test port (schrader valve) on the fuel rail.
    
   
2. START the engine and allow it to idle, then note the fuel pressure. If the pressure is within specification, proceed to step 3. If the pressure is above or below specification, proceed to FUEL SYSTEM DIAGNOSIS for further testing.
    
   
3. STOP the engine, noting the gauge reading. Allow the engine to sit, with key OFF for 30 minutes, then recheck the fuel pressure gauge. A pressure drop of 0-138 kPa (20 psi) from the specified operating pressure is normal, and no further fuel pump testing is necessary. If the fuel pressure drop is greater than that specified, proceed to step 4.
    
   
4. START the engine and allow it to idle. Simultaneously pinch the fuel return hose, and STOP the engine. Note the fuel pressure reading. Allow the engine to sit for 30 minutes, with the fuel return line pinched, and recheck the pressure reading. If the pressure has dropped 0-138 kPa (20 psi) or less, replace the fuel pressure regulator. If the pressure drop still exceeds the specified amount, the fuel pump check valve is leaking, and the pump will need to be replaced.
   

engine at curb idle

 

vacuum hose connected: 31 psi

 

vacuum hose disconnected: 39 psi

[MJCARENA]

My fuel pressure drops to 18 overnight, so I think my check valve and regulator are good.

[1989 Eliminator]

I had the same issue as you and it is very possible it is your CPS sensor. (crankcase position sensor) Give me a few and ill find the fourm page about this. :thumbsup:

[1989 Eliminator]

This website helps:

 

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

 

This is the fourm I was talking about:

 

Test the CPS first.

 

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

 

. :MJ 1: .

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[1989 Eliminator]

http://comancheclub.com/topic/34942-1989-renix-no-start-condition-issue/

 

This was my fourm about the same topic

 

Good luck.

[MJCARENA]

Tried to start her when I got home and would not start. Measured my CPS by backprobing while cranking it .39 volts ac. I don't see that as a problem since I do have spark. Checked the adjustment of the TPS and it is good. Used starting fluid and it started right up. My CPS is putting out 1.25 volts ac at idle. Drove it around for about 15 minutes. Drives normal, accelerates good.At idle in gear it feels like a very small miss. Idle is around 600 rpm in gear. Turned on the ac and it maintained 600 rpm, but still just a little rough idle. Got home and since it is up to operating temp it starts every time. Waited about an hour and it still starts. My CPS still measured .39 volt ac when cranking. Will try again in the morning when it has cooled down. Going to change my fuel filter tomorrow also, since I don't remember ever changing it. The air filter is clean looking, blew it out anyways.

[cruiser54]

CPS should be checked unplugged. Which side of the TPS did you check?

[MJCARENA]

CPS should be checked unplugged. Which side of the TPS did you check?

 

My CPS has the factory mod done to it, eliminated the connector and replaced the wires/pins going to the ECU. I would have to undo the soldered splice to disconnect the TPS to measure it. Will do this tomorrow and get a reading on it.

I did the square plug for automatics. Measured D to A (4.65) and D to B (3.85) then did the math and came out to .827 My book says it should be .83

[cruiser54]

My CPS has the factory mod done to it, eliminated the connector and replaced the wires/pins going to the ECU. I would have to undo the soldered splice to disconnect the TPS to measure it. Will do this tomorrow and get a reading on it.

I did the square plug for automatics. Measured D to A (4.65) and D to B (3.85) then did the math and came out to .827 My book says it should be .83

 

The factory mod should still have a plug. Maybe it's a dealer mod?

 

For driveability issues, the flat 3 wire connector should be used. There are 2 separate units in that TPS. Checking the trans side doesn't mean the engine side is good.

 

 

RENIX TPS ADJUSTMENT

Before attempting to adjust your TPS be sure the throttle body has been recently cleaned. It's especially important that the edges of the throttle butterfly are free of any carbon build-up.

IMPORTANT NOTE: With the Key OFF, and 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 parallels the valve cover and also over near the MAP sensor on the firewall. If you see more than 1 ohm of resistance, or fluctuation in your ohms reading, some modifications to the sensor ground harness will be necessary. The harness repair must be performed before proceeding. I can provide an instruction sheet for that if needed.

MANUAL TRANSMISSION:

RENIX manual transmission equipped XJs have only a flat three-wire TPS mounted on the throttle body and it provides data input to the ECU. It has three wires in the connector and they're clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors. Note the voltage reading--this is your REFERENCE voltage. Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For example: 4.82 volts X .17=.82 volts. Loosen both T-20 Torx screws attaching the TPS to the throttle body and rotate the TPS until you

have achieved your desired output voltage. Tighten the screws carefully while watching to see that your output voltage remains where it is supposed to be. If you can't achieve the correct output voltage, replace the TPS and start over.

Sometimes, after adjusting your TPS the way outlined above, you may experience a high idle upon starting. If that happens, shut the engine off and reconnect your probes to B and C. Start the engine and while watching your meter, turn the TPS clockwise until the idle drops to normal and then rotate it back counterclockwise to your desired output voltage.

AUTOMATIC TRANSMISSION: RENIX automatic transmission equipped XJs have a TPS with two connectors. There is a flat three-wire connector, same as the manual transmission vehicles have, and it is tested the same as the manual transmission equipped vehicles, as outlined above—FOR ALL ENGINE MANAGEMENT RELATED ISSUES.

However, the automatic TPS also has a square four-wire connector, clearly embossed with the letters A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module. THIS SQUARE FOUR WIRE CONNECTOR IS USED FOR TRANSMISSION/SHIFTING RELATED ISSUES ONLY. Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your REFERENCE voltage. Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage. For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage. If you can't, replace the TPS and start over. So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and the other side feeds the TCU.

FOR AUTOMATIC TRANSMISSION RELATED ISSUES: Check the square four-wire connector side of the TPS.

If you have ENGINE ISSUES check the flat three-wire connector side of the TPS.

For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.

Revised 09-22-2012

[MJCARENA]

I will check out the flat connector, and yes it is the dealer mod on the CPS.

[MJCARENA]

Measured my CPS again with it disconnected and got .30 volts. So I will try to get it higher by slotting it or get another one. Would not start today with the engine cold. Going to work on it tomorrow.

[cruiser54]

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 to 3/8” from the stock 5/16”, 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 01-26-2013

[MJCARENA]

Worked on it this morning. Slotted my CPS and now have .55 volts from it disconnected, Reconnected it and still won't start. Measured and adjusted my TPS using the flat connector. Still no start. Changed out my fuel filter, no help. Swapped computers from my 1989 XJ. The XJ starts with the Comanche computer, but the Comanche doesn't start with the XJ computer. Unplugged and replugged just about every connector under the hood,no help. Plugged in my spare Coolant Temp Sensor, just left it hanging, and she starts, tried it about ten times and she started every time. Going to let it sit for a couple of hours and check again. Hope this was it.

[MJCARENA]

Tried it again and it starts, going for a ride. Still not sure this was it, will give it a few days before I have confidence in it again.

[cruiser54]

Tried it again and it starts, going for a ride. Still not sure this was it, will give a few days before I have confidence in it again.

 

Interesting...

[MJCARENA]

Tried it this morning and just now, she started right up both times, looking good. I still have to mount the sensor.

[cruiser54]

When you bypassed the C101, did you solder or use butt connectors?

[MJCARENA]

When you bypassed the C101, did you solder or use butt connectors?

 

I soldered them and used heat shrink.

 

 

[cruiser54]

Good.

 

Have you tried wiggling the harnesses under the hood when the problem occurs?

[MJCARENA]

Yes I moved the wire harness when cranking. I have done the sensor ground test and upgrade when I did the C101 bypass. I did have bad crimps in the harness, soldered the splices and the ground test was good after that. I have read your tips and applied most of them. Started right up this morning and drove it to work. Ran smooth.

[MJCARENA]

So far it has started every time. I would like to thank all of you for your help and advice.