HELP! cant figure this one out

Hey all,
I have an 86 Comanche 2.5L 4SPD. This thing will not start on it's own when it is cold. In the summer it isn't so bad, it will at least start and I can keep it running, but not in this cold winter weather. If I put gas down the TB it will fire right up and run till that gas is gone. After a few times of doing this I can keep it running by feathering the gas pedal till it warms up. Once it's warm it runs fine all day till it cools off. Passed Ohio E check with flying colors. I have replaced the CTS and did a complete tune up. I have tested all the sensors by the book and they all seem to check out to specs. All the grounds I could find are good. I also replaced the processor with a known good one and it does the same thing. Can someone please point me in the right direction, I really need to get this thing running. Thanks for any help you can provide

Did you check the ground in your drivers side tail light bucket?

On your MJ the fuel pump shares that ground. Pop off your tail light and check that ground, sounds like a fuel problem and could be caused by a shaky connection there.

No I haven't looked there. The injector is squirting even when it won't start but it seems that it isn't enough fuel to fire the cold engine. One it warms up it runs and drives all day long without a problem. Wouldn't a bad ground to the fuel pump cause it to not pump at all? Or at least cause it to cut out intermittently? I will check anyways, I'm open to any suggestions at this point. I'm to the point now of pulling the wiring harness to the processor and going through each wire individually to maybe find a bad one.

I would check the trottle body paying carefull attention to the IAC. It may be advatageous to remove and clean it as well as the cavity in which it sits. You could try to sustitute a know good IAC while you are at it.

The IAC takes the place of the strangler flap in carbeurettors. It closes and opens an air passage in the trottle body to allow the engine to richen up when the engine is cold then lean out when the engine warm up.

dgates0202 said:

Wouldn't a bad ground to the fuel pump cause it to not pump at all? Or at least cause it to cut out intermittently?

Click to expand...

Maybe...just something else to check...cleaning IAC sounds like a good idea too.

...and, I said a "shaky" ground, not NO ground.

techno1154 said:

I would check the trottle body paying carefull attention to the IAC. It may be advatageous to remove and clean it as well as the cavity in which it sits. You could try to sustitute a know good IAC while you are at it.

The IAC takes the place of the strangler flap in carbeurettors. It closes and opens an air passage in the trottle body to allow the engine to richen up when the engine is cold then lean out when the engine warm up.

Click to expand...

This system doesnt have that type of IAC, like fords and gm's. It has and Idle Speed solenoid Not an idle air control, two different things. It doesnt have a cavity, it is totally external. And I did clean the TB and the solenoid is working properly. I checked the ground to the pump just a bit ago and it is good.

dgates0202 said:

This system doesnt have that type of IAC, like fords and gm's. It has and Idle Speed solenoid Not an idle air control, two different things. It doesnt have a cavity, it is totally external. And I did clean the TB and the solenoid is working properly. I checked the ground to the pump just a bit ago and it is good.

Click to expand...

If you do not have an IAC then I would assume you have a carbeuretored engine thus a solonoid to kick up the idle when the engine is cold. That means it should have a strangler flat, ie. the top butterfly in the carbeurettor. Check the linkages on it to see if it closes when the engine is cold. Clean and lubricate if the parts are in good condition. Repair or replace bad or worn parts and lubricate as needed.

I may be way off here since I have never seen a carbeuretored XJ. I know they exsist. I am just reaching back into my memory of cars from the 60's and 70's Someone who is familiar with these would give you more help than I can.

techno1154 said:

If you do not have an IAC then I would assume you have a carbeuretored engine thus a solonoid to kick up the idle when the engine is cold. That means it should have a strangler flat, ie. the top butterfly in the carbeurettor. Check the linkages on it to see if it closes when the engine is cold. Clean and lubricate if the parts are in good condition. Repair or replace bad or worn parts and lubricate as needed.

I may be way off here since I have never seen a carbeuretored XJ. I know they exsist. I am just reaching back into my memory of cars from the 60's and 70's Someone who is familiar with these would give you more help than I can.

Click to expand...

No this is a throttle body injection, hence I stated TBI, and yes I know the difference. It does NOT have an IAC it has an idle speed solenoid. Fuel injection does not use a choke as you described. It uses input from the CTS and other sensors to meter the fuel delivery. As far as I know 1986 was the first year MJ Comanche and they were all injected, The earlier XJ Cherokee's were carb but all were injected after 1986. This is a very simple system which is why it is so frustrating that I cant figure this out. I was just hoping someone with experience in these Renix FI systems would have an idea, something odd they may have run across in the past. Everything so far has tested within specs and I even tested the wiring harnes, in and out of the truck, nothing wrong there either. It acts like it isnt getting a signal from the cts to the processor but it is. Again this is only a cold start problem, it runs perfect and starts everytime when it is warm. Anyways i do know for a fact it has no carb or choke or iac. But thanks for trying

Well, if the CTS was bad and telling the ECU the engine is hot then it would be a "B" to start in cold weather.

Other things in cold weather: Things contract. So, grounds that haven't been "renewed"--taken down to bare metal, cleaned, treated with an anti-corrosive, and then tightened, will end up making lousy contact when cold. Did you "renew" all of the grounds, or just "check" them?

Not that familiar with the TBI and 2.5 in the early XJ. Do you have the FSM for your year? Does your XJ utilize a crank position sensor and/or a B Latch relay?

joe_peters said:

Other things in cold weather: Things contract. So, grounds that haven't been "renewed"--taken down to bare metal, cleaned, treated with an anti-corrosive, and then tightened, will end up making lousy contact when cold. Did you "renew" all of the grounds, or just "check" them?

Not that familiar with the TBI and 2.5 in the early XJ. Do you have the FSM for your year? Does your XJ utilize a crank position sensor and/or a B Latch relay?

Click to expand...

x2 on all this.



edit****
"if I put gas down the TB it will fire right up and run till that gas is gone. After a few times of doing this I can keep it running by feathering the gas pedal till it warms up. Once it's warm it runs fine all day till it cools off."

sounds like a fuel issue. Like Joe stated, I myself am not that familiar with the TBI xjs. DO you have one or two injectors? Have you ever had them cleaned with an injector cleaning machine? Have you checked fuel pressure when the no start condition exists? Before you pour gas down the TB.

Taken from the FSM.
"Closed Throttle (Idle) Switch
This switch is integral with the idle speed actuator (ISA)
motor. The switch provides a voltage signal to the ECU, which
increases or decreases the throttle stop angle in response to engine
operating conditions."
I'd look into this if I were you

"The fuel pump is controlled by the ECU. A ballast resistor attached to the right side of the plenum chamber,
reduces fuel pump speed after engine is running. The resistor is
by-passed in the "Start" position."
Maybe its not by-passing the ballast resistor?

"fuel pressure of 17.3 psi"
There your spec for fuel pressure if you check it

ENGINE START-UP MODEWhen the starter motor is engaged, the ECU receives inputs
from the CTS and speed sensors, the starter motor relay, and the wide
open throttle switch. The fuel pump is activated by the ECU and
voltage is applied to the injector, with the ECU controlling
injection time.
The ECU determines proper ignition timing from the speed
sensor input. If the wide open throttle switch is engaged, the ECU
will deactivate the injector to prevent flooding.

ENGINE WARM-UP MODE
The ECU receives inputs from the CTS, MAT, MAP, speed, and
knock sensors. It also is informed of throttle, gear (automatic
transaxle models) and A/C control position.
The ECU provides a ground for the injector, precisely
controlling fuel delivery to the engine. The ECU also controls
ignition timing, engine idle speed and throttle stop angle. On
vehicles with manual transmissions, the up-shift indicator lamp is
controlled according to engine speed and load.




Diagnosis
CLOSED THROTTLE SWITCH
NOTE: It is important that all testing be done with the idle speed
actuator (ISA) motor plunger in the fully extended position
(as it would be after a normal engine shut down). If it is
necessary to extend the motor plunger to test the switch, an
ISA motor failure can be suspected. Refer to ISA motor test.
1) With ignition on, connect voltmeter positive lead to pin
13 of diagnostic connector D2. Attach negative lead to pin 7. Voltage
should be close to zero at closed throttle and greater than 2 volts
at any position other than closed throttle.
2) If the voltage is always zero, test for a short circuit
to ground in the wiring harness or switch. Test for an open circuit
between pin 25 of ECU connector and throttle switch.
3) If voltage is always more than 2 volts, test for an open
circuit in the wiring harness between the ECU and switch connector.
Also check for open circuit between the switch connector and ground.
Repair or replace wiring harness as needed.


**EDIT**


I found a link that has all of this in it. Read the diagnosis part and do the Pin tests.

http://jeepgarage.free.fr/OWN/2.5l%20cec%20system.pdf