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ctxj93

88 comanche hard start or no start when cold

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Hi Everyone,

I'm having problems with cold starts on my 88 MJ. So far I've:

-Tested and refreshed the grounds

-Adjusted TPS to spec 

-Swapped in a known good IAC,  

- Checked the cps when cranking (I have .498V AC) 

- Made sure the Coolant temp and intake air temp sensors are working as they should. 

- Checked fuel pressure- I have 39 psi that holds steady 

-Checked timing and made sure distributor was installed correctly

-Checked for o2 sensor heater voltage 

-swapped relays around 

-EGR is blocked off

-Checked for vaccuum leaks 

-swapped known good Coil and ICM

-swapped known good ECU

 

When the truck does start, usually after several extended cranks,  it doesn't start like any other renix I've owned. Instead of revving up to somewhere over 1k and coming back down to ~750,  it sort of stumbles to life and comes up to the 750 mark.  All of this only happens if the truck has been sitting for a while. Once I've had it running, it still stumbles to life, but it will always start. 

 

Once it's running, it idles nice and smooth and revs through the rpms with no backfires or hiccups. 

 

I'm wondering if this could have something to do with the B+ latch relay? Maybe the IAC isn't returning to the correct position on shutdown? 

 

I also noticed that on the green to 3 red wire fusible link coming off of the starter solenoid, one of the red wires just deads ends. There also is an additional red wire running from the ring connector at the solenoid that runs all the way across the back of the motor and through the firewall on the driver's side.  Is it possible the previous owner hacked some additional wiring in here that bypasses the B+ latch relay?  

 

Any help would be appreciated. I've done my best to research people having similar issues, but haven't found any solution yet. I'm starting to lose my mind. 

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23 minutes ago, ctxj93 said:

I'm wondering if this could have something to do with the B+ latch relay?

Check B+ Latch Relay. Connect DVOM or testlight to D2-5. When KEY is cycled ON should have B+. When KEY is cycled OFF, should hold B+ for a few seconds afterwards.

D1_D2.jpg.8c829f66c33f4f335bc80fc6b2d2baea.jpg

 

24 minutes ago, ctxj93 said:

Checked fuel pressure- I have 39 psi that holds steady

Does fuel pressure drop to 31psi at idle?

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3 minutes ago, Ωhm said:

Check B+ Latch Relay. Connect DVOM or testlight to D2-5. When KEY is cycled ON should have B+. When KEY is cycled OFF, should hold B+ for a few seconds afterwards.

D1_D2.jpg.8c829f66c33f4f335bc80fc6b2d2baea.jpg

 

Does fuel pressure drop to 31psi at idle?

Yes sir, fuel pressure drops to 31 at idle.  Thank you for the B+ diag info, I'll have to test it tomorrow. 

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Ok, just ran out and checked it in the dark, D2-5 has 11v with key on, key off it starts dropping down over a few seconds eventually getting to <0.2v

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4 minutes ago, Ωhm said:

Check out Cruisers Tips 11 & 14.

http://cruiser54.com/

I cleaned the Throttle body really well, and the whole intake and all sensors came off of my other MJ which ran and started perfectly. I will check the butterfly adjustment just to be sure.  Thanks!

 

This comanche I'm working on now had an HO swapped in, and the PO tried to just wire the new style sensors to the renix harness. It did not go well. I reverted everything back to renix. 

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Original or HO injectors?

 

Best to use are the Volvo injectors refurbished. jhc7399 on Cherokee forum rebuilds them. 

Vacuum leak where intake manifold meets head by chance?

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10 hours ago, cruiser54 said:

Original or HO injectors?

 

Best to use are the Volvo injectors refurbished. jhc7399 on Cherokee forum rebuilds them. 

Vacuum leak where intake manifold meets head by chance?

19lb mustang injectors, also came off a running MJ. 

 

I checked around with carb clean pretty thoroughly, I've had vaccum leaks at the manifold on another jeep and it resulted in a noticeably high idle and whistling sound from that area of the motor.  I'm using the renix intake and exhaust manifolds on the HO block.

 

This truck has been hard to start ever since I've owned it.  I figured it was due to the butchered sensor set up that it had when I first got it, but even now with all the right parts it's still giving me problems! 

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Did you use the Renix intake gasket?

 

You have ALL Renix sensors now, right? 

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3 hours ago, cruiser54 said:

Did you use the Renix intake gasket?

 

You have ALL Renix sensors now, right? 

Yep Renix intake gasket and all sensors.  It's weird sometimes I get 3 or 4 normal sounding 4.0L starts, and then it's back to the lumpy starts without the normal rev up over 1k

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On ‎10‎/‎14‎/‎2019 at 7:21 PM, ctxj93 said:

Hi Everyone,

I'm having problems with cold starts on my 88 MJ. So far I've:

-Tested and refreshed the grounds

-Adjusted TPS to spec 

-Swapped in a known good IAC,  

- Checked the cps when cranking (I have .498V AC) 

- Made sure the Coolant temp and intake air temp sensors are working as they should. 

- Checked fuel pressure- I have 39 psi that holds steady 

-Checked timing and made sure distributor was installed correctly

-Checked for o2 sensor heater voltage 

-swapped relays around 

-EGR is blocked off

-Checked for vaccuum leaks 

-swapped known good Coil and ICM

-swapped known good ECU

 

When the truck does start, usually after several extended cranks,  it doesn't start like any other renix I've owned. Instead of revving up to somewhere over 1k and coming back down to ~750,  it sort of stumbles to life and comes up to the 750 mark.  All of this only happens if the truck has been sitting for a while. Once I've had it running, it still stumbles to life, but it will always start. 

 

Once it's running, it idles nice and smooth and revs through the rpms with no backfires or hiccups. 

 

I'm wondering if this could have something to do with the B+ latch relay? Maybe the IAC isn't returning to the correct position on shutdown? 

 

I also noticed that on the green to 3 red wire fusible link coming off of the starter solenoid, one of the red wires just deads ends. There also is an additional red wire running from the ring connector at the solenoid that runs all the way across the back of the motor and through the firewall on the driver's side.  Is it possible the previous owner hacked some additional wiring in here that bypasses the B+ latch relay?  

 

Any help would be appreciated. I've done my best to research people having similar issues, but haven't found any solution yet. I'm starting to lose my mind. 

Could weather be playing a part in this problem? Have you inspected dist. cap button to rotor contact, tracking inside cap, sometimes a spray bottle of water and misting around ing. cap and wires will show arcing best seen at night or low light, a lot of times wet engine will act like this. I ask this after seeing you are in CT. and your XJ pic shows snow. How long has this been gong on?

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41 minutes ago, Warren Mohler said:

Could weather be playing a part in this problem? Have you inspected dist. cap button to rotor contact, tracking inside cap, sometimes a spray bottle of water and misting around ing. cap and wires will show arcing best seen at night or low light, a lot of times wet engine will act like this. I ask this after seeing you are in CT. and your XJ pic shows snow. How long has this been gong on?

I've owned this MJ for a little over a year.  I noticed the extended crank right off the bat before purchasing the truck. It currently has the dizzy off my old comanche, a brand new cap, rotor and wires.  Everything is dry under the hood, i didnt notice any tracking inside the cap, and weather doesnt seem to make a difference, it has this problem year round. 

 

Pic attached purely because I'm super excited to drive this thing (if I can ever get it running right) 

20190928_210834.jpg

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14 minutes ago, ctxj93 said:

I've owned this MJ for a little over a year.  I noticed the extended crank right off the bat before purchasing the truck. It currently has the dizzy off my old comanche, a brand new cap, rotor and wires.  Everything is dry under the hood, i didnt notice any tracking inside the cap, and weather doesnt seem to make a difference, it has this problem year round. 

 

Pic attached purely because I'm super excited to drive this thing (if I can ever get it running right) 

20190928_210834.jpg

I had hot starting problems do to fuel leaking through pressure reg. Several other members found same problem. I am waiting to hear from them if replacing reg. cured their problems as well. Depending on amount of fuel leaking into intake could also cause cold problems. All of us with this leak had good pressure that seemed to hold, worth a check

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Make sure your intake manifold bolts are not loose.

 

THROTTLE BODY TO MAP SENSOR HOSE FIX

The Renix throttle bodies have a strange and failure prone connector on the side where the MAP supply originates and then runs up to the MAP sensor located on the firewall. This hose/pipe assembly is no longer available for purchase.

The real kicker here is how critical this line is in supplying the correct vacuum signal to the MAP, the most relied upon sensor for the ECU to read regarding air/fuel ratio. Any cracks, melted spots, or loose rubber connectors can cause major starting and driveability issues.

There’s a simple fix though. All that’s required is a 1/8” NPT tap, a new throttle body gasket ( Napa FPG 60742 ), a vacuum fitting (Napa 05703-B102), two vacuum elbows (Napa CRB2670), and a length of new plastic piping (Napa CRB2672).

1-20160126_155433

Remove the throttle body and take it to the workbench.

Using an oiled tap along with a driver, carefully thread the lower of the 2 holes of the throttle body where the old fitting was plugged in. Don’t go too deep. These are pipe threads.

Flush the hole with carb cleaner and inspect for any left over cuttings.
This is an excellent time to do a complete throttle body and IAC cleaning.  See Tip 11.
Take the vacuum fitting (05703-B102 ) and apply a LITTLE bit of thread sealer on the threads only. I prefer Permatex #2 but almost anything is fine.

.1-TB to MAP hose-001

Carefully screw the fitting in until snug.

Install one of the vacuum elbows on the MAP sensor so it points toward the throttle body, and the other vacuum elbow on your new throttle body fitting so it points up to the MAP sensor.
Cut a length of the new plastic tubing (approximately 13 inches) to fit between the vacuum elbows and install it making sure there is enough slack for some engine movement. Route it according to the photo. We don’t want any rubbing or chafing with engine movement.  Not a bad idea to use some contact cement or Gasga-Cinch sparingly on the tubing to elbow connectors.

1-TB to MAP hose

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On 10/16/2019 at 10:08 AM, cruiser54 said:

Have you actually indexed the distributor? 

The previous owner cut the locating tab off the distributor to make it adjustable. I messed with this adjustment a little bit and decided I should eliminate this variable. I swapped in a distributor off my other truck and followed the instructions for indexing. I checked the timing with a light and it was within spec. 

 

I swapped in a new IAC, although I'm not sure was really the correct one for the truck even though it was listed as such. It doesn't seem to make a difference in  idle plugged in vs unplugged.  I also checked the short section of rubber fuel line on the fuel pump to make sure it wasn't deteriorated.  It looked fine.  The truck starts pretty much everytime but I'm still not happy with the crank time and stumbling to life.  

 

When I was checking relays last month, it seemed like if I unplugged a relay and plugged it back in I would get a few good starts and then it would revert back to stumble city.  Pretty frustrating! 

 

My MAP line seems to be fine, it also came off a running truck but I will fix it as you described and report back. 

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Good plan. The MAP line needs a thorough inspection. Long crank time is pretty standard.

 

I'm concerned with your dizzy indexing still. Timing light has no bearing on this. 

It must be done only according to the instructions using a cut-away cap. 

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Interested to see if a solution to this problem can be found, I have the same issue with a 88 4.0l renix MJ. On cold starts the engine turns over for probably about 6 seconds before starting and does not rev up to 1k and come back down to around 750, instead it stumbles to life and idles around 150 rpm and after a minute or two it adjusts to 750 rpm. Sometimes I have to give it a little throttle or it will stall before the idle comes up. About 40 percent of the time the truck will continue to idle too low after stumbling to life and never idle at the correct speed. Rarely when it gets warm it will idle too high(1200 rpm). This problem seems to be intermittent, If the engine is warm and the idle is too low(300-400 rpm) and i shut it off and restart the engine the truck fires right up to 1000 rpm and comes down to around 750 and idles normal. Also it should be noted, Other than the strange idle the truck runs fine, No miss fire, or skipping, or loss of power, runs down the road fine. 

 

-NEW IAC

-NEW  TPS, adjusted correctly

-Perfectly clean Throttle body

-NEW MAP, with new map vacuum line

-NEW Plugs, wires, cap, rotor

-IAT Checks out

-CTS Checks out

-CPS Checks out

-EGR is deleted

-02 sensor checks out

-C101 is deleted

-All grounds have been cleaned and refreshed

-Fuel Pressure is good

-Swapped all the relays out, no change

-NEW intake manifold gasket and the bolts are torqued to spec

-Previous owner redid most of the vacuum lines, can't find a leak

-Has a REMAN BENDIX ECU that was installed back in 2002

 

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Just away out there thought.....Both say that you have new plugs and wires

Just old school curious......what color is your spark?

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42 minutes ago, yxmj said:

Just old school curious......what color is your spark?

how are the plugs? are they black? does it blow black smoke when it does start?

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My plugs still look new, and it doesn't smoke at all.  Went to the boneyard and picked up another ecu. Swapped it and haven't had any issues for the past two days. Starts and idles perfect. Guess my problem was the ecu. 

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