Starting Trouble

[Hudy]

I had posted about this some time ago, but I’m starting a new thread as that one evolved into a fuel pressure issue.

5 years with this truck, and this is still a mystery. Now I’m determined to get this solved. 

 

If my MJ is HOT, that’s to say I’ve driven it and brought it up to temp, it doesn’t like to restart. I’ll have to give it 3 or 4 cranking attempts before it will start. By this I mean I’ll crank the starter for 3 or 4 seconds, stop and repeat this 3 or 4 times before it starts. 

 

If I allow the truck to cool all the way down, or if it’s a morning start, it fires right up. Every time. 

 

1. I have great fuel pressure and it holds fuel pressure. 

2. I have spark during this no-start period. I’m determining that with an in-line spark tester. 

3. I would THINK the injectors are working as I can smell fuel when the truck finally starts up. 

4. CPS values are where they should be determined by cruiser54’s guide. (Right around .7 ACV)

5. I’ve added multiple additional ground points. OHMs from the TPS to battery are around .05

6. Coil and relay contacts were cleaned. 

 

I have not tested compression but if this was an issue, I’d think id have this symptom all the time. 

 

Am I missing something? Is it possible I have spark but it’s not sufficient for running conditions? And if so why would heat affect this? Do sensor values control fuel in some way versus spark?

 

 

[cruiser54]

Have you tested the CPS output when hot?

[Hudy]

48 minutes ago, cruiser54 said:

Have you tested the CPS output when hot?

 

Yes. The .7 ACV is when hot. 

[cruiser54]

You could test it at the ECU. Maybe something is getting lost in the wiring. 

 

 

[Hudy]

On 9/20/2019 at 10:16 AM, cruiser54 said:

You could test it at the ECU. Maybe something is getting lost in the wiring. 

 

 

 

Which connector would you recommend probing? 

[cruiser54]

Probe C1 And D1 just like you would test the cPS in the engine bay.

[Hudy]

1 hour ago, cruiser54 said:

Probe C1 And D1 just like you would test the cPS in the engine bay.

 

Same readings. 

 

I did “refresh” the connectors while it’s out. 

Also cleaned grounds in the engine bay. In my case, I have both ground terminals from the cab AND the (-) battery terminal all grounding at the dip stick stud.

 

I do have extra ground wires at the rear of the intake manifold and also at the battery. 

[Hudy]

Another point to add: the gauge cluster voltmeter has always read low. Typically around 13 when running, and sometimes as low as 12 with the headlights on and fans on high. Voltage at the battery remains at ~14. 

[Ωhm]

Check for ≈6 ohms across the O2 Heater Circuit. Measure between D2-9 and D1-3.

 

 

[Hudy]

2 hours ago, Ωhm said:

Check for ≈6 ohms across the O2 Heater Circuit. Measure between D2-9 and D1-3.

 

 

OHM reading is 2.4

 

[fiatslug87]

Check the resistance of the O2 sensor itself between terminals A&B, should be between 5-7 ohms. Just to make sure it's not just the wiring.

[Hudy]

23 hours ago, fiatslug87 said:

Check the resistance of the O2 sensor itself between terminals A&B, should be between 5-7 ohms. Just to make sure it's not just the wiring.

with the truck completely cold, OHM at the sensor is 4 and at the diagnostic port 1.3.

 

Also tested the IAT today which was faulty; reading significantly LOW based on temp and not climbing normally.

[Ωhm]

Generally speaking, O2S heater circuit goes OPEN. Good find on the IAT. Check ECT, also a known problem for hot starting issues.

[Hudy]

14 hours ago, Ωhm said:

Generally speaking, O2S heater circuit goes OPEN. Good find on the IAT. Check ECT, also a known problem for hot starting issues.

I have a spare ECT that tested as good, I’ll install that today. 
 

Still have the hot start trouble today (x3) with the IAT replaced, although it is definitely starting sooner. 

[coolwind57]

EXACT issues here, Hudy so I feel your pain.  I'd posted about it in the past too.  Delayed starting after excessive cranks with significant gas smell when it does come to life.  I've been dealing with it for the last year or two.  I've replaced nearly every component with an abbreviation plus many more parts involving the starting and general operation of the engine.

 

Reading with great interest.  Dying to find a culprit.

[Hudy]

Can anyone chime in with a list of what’s needed from start to finish for start? For instance;

Key To Start

Starter must reach 300rpm

CPS send signal to ECU

ECU sends power to ICM for spark

ECU determines fuel ratio based on:

A. CTS reading

B. manifold temp reading

 

etc etc etc...

 

 

[Hudy]

On 9/24/2019 at 10:03 AM, coolwind57 said:

EXACT issues here, Hudy so I feel your pain.  I'd posted about it in the past too.  Delayed starting after excessive cranks with significant gas smell when it does come to life.  I've been dealing with it for the last year or two.  I've replaced nearly every component with an abbreviation plus many more parts involving the starting and general operation of the engine.

 

Reading with great interest.  Dying to find a culprit.

There absolutely has to be a cause. I’m determined to figure this out. 

[eaglescout526]

Ok, after a couple years of perusing the forum in my boredom I came across a post. Some one said that the coil with age is prone to getting hot and causing start issues. How old is the coil? Is it the factory one?

[Ωhm]

For your reading enjoyment. Modes of Operations start on pg76.

Jeep FI Manual

 

For real time data, checkout Renix Engine Moniitor (REM).

R.E.M.

 

I'll take it that the ECT sensor didn't help your HOT START issues.

 

[Hudy]

1 hour ago, eaglescout526 said:

Ok, after a couple years of perusing the forum in my boredom I came across a post. Some one said that the coil with age is prone to getting hot and causing start issues. How old is the coil? Is it the factory one?

Looks to be the factory coil. Interesting point as I have a friend who’s metropolitan ran into the same issue, except in his situation it wouldn’t start at all, in fact it would die while running. In my case I can run hot all day. And after a few starting attempts, it does start and runs fine. So would repeated start attempts revive a tired coil? Could be the cause, but this just seems to be a sensor issue to me. 

[Hudy]

58 minutes ago, Ωhm said:

For your reading enjoyment. Modes of Operations start on pg76.

Jeep FI Manual

 

For real time data, checkout Renix Engine Moniitor (REM).

R.E.M.

 

I'll take it that the ECT sensor didn't help your HOT START issues.

 

helpful info, thanks! Haven’t swapped the sensor yet, busy chasing the kid around the house the past few days. Hoping for time this weekend. I’ll read these documents tomorrow.

[eaglescout526]

1 minute ago, Hudy said:

Looks to be the factory coil. Interesting point as I have a friend who’s metropolitan ran into the same issue, except in his situation it wouldn’t start at all, in fact it would die while running. In my case I can run hot all day. And after a few starting attempts, it does start and runs fine. So would repeated start attempts revive a tired coil? Could be the cause, but this just seems to be a sensor issue to me. 

Well lets think about it a second. Sometimes sitting and looking at the engine bay helps(with me at least). So how does she run? Idle? Under load? If everything is smooth and as it should be like she left the factory and just trying to start up again is a drag, I would look at the coil. Buy a cheap one and throw it in there and give a whirl. If it solves your hot start then you got it. If not then you are back to a sensor problem like you are saying.

[coolwind57]

I've got a new ignition coil that should arrive today, but I won't get an opportunity to install it till tomorrow.  This has been a slow and steady parts-cannon approach for me, as I've replaced and properly tuned/adjusted nearly everything possibly associated with this issue.  I'll let you know what happens.

 

Only two other things I can think of that I hadn't yet done:  a new fuel pump and Cruiser54's injector harness crimp repairs, both of which I'd deemed least likely a cause.  

.

 

 

[coolwind57]

ok new coil installed.  Honestly, I have my doubts but I found an extra 20-bucks and bought this part so why not try.  Will report back in a couple of days with results or disappointments.  Here's a comparison between the old and new:

 

The NGK is a bit thinner, but has all copper contacts.  The stock one has copper contacts below, but a silver-colored contact where the coil wire fits.  NGK cover completely surrounds the stacked plates, where the old stock one surrounds 3 sides only. 

 

There were several other aftermarket brands available that were cheaper, but opted for the NGK due to brand recognition and reputation.  

 

 

[Hudy]

Coolwind, I'm excited to see how that might help. 

 

Interesting update on my end: I had the truck running from job to job yesterday and it was starting great. I couldn't believe it. Then I noticed that the truck wasn't getting to temperature, instead it was floating around 175*. Verified the temp with a heat gun on the themostat housing. So, I'm assuming the thermostat is stuck open and I ordered a replacement. 

This now brings me to this: could it be that the computer doesn't know what to do, or perhaps grossly miscalculates the values when it sees an open loop reading from the CTS? 

 

Also found a friend with an MT2500 that ill be borrowing for a few days so I can see what the sensor readings are when this tough start issue presents itself.