1990 Cherokee injectors not firing
It's an auto. Anybody heard of the TSB with the slotted CPS and new gasket? I'm sure I have the original gasket. Do you think this could be the problem? Here is the link http://autorepair.about.com/library/a/1h/bl557h.htm
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Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
It's an auto. Anybody heard of the TSB with the slotted CPS and new gasket? I'm sure I have the original gasket. Do you think this could be the problem? Here is the link http://autorepair.about.com/library/a/1h/bl557h.htm
So I tested the injectors and they have a good ground on one Leg. So I guess I'm back to the cps? How could two new cps be bad? Is there an adjustment to it that I'm getting wrong? Are there shims to keep it off the flywheel that I'm missing? Should I take the gasket out and try it without a gasket? I did test it and the ac volts were around .25 but I figured my meter was off because it's a cheap one.
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
So I tested the injectors and they have a good ground on one Leg. So I guess I'm back to the cps? How could two new cps be bad? Is there an adjustment to it that I'm getting wrong? Are there shims to keep it off the flywheel that I'm missing? Should I take the gasket out and try it without a gasket? I did test it and the ac volts were around .25 but I figured my meter was off because it's a cheap one.
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
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Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
So I've removed the cps gasket and drilled out the cps. I'm now getting 4-5 v ac from the cps. The fuel injectors are firing now but still won't start. Verified spark at plugs. Shot starting fluid down throttle body and it won't even pop. Verified 40 lbs fuel pressure. Please help.
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
So I've removed the cps gasket and drilled out the cps. I'm now getting 4-5 v ac from the cps. The fuel injectors are firing now but still won't start. Verified spark at plugs. Shot starting fluid down throttle body and it won't even pop. Verified 40 lbs fuel pressure. Please help.
It must b timing right? I retested the cps and it's back down to .3v AC. I keep coming back to the cps. I guess I'm going to get one from the dealer and see if it works. But the plugs are sparking and the noid light is blinking. But when I dump starting fluid into the intake it won't even hit.
Another weird thing is I get fumes and smoke out of the Crankcase vent in the top of the valve cover. I converted it to just a breather because I was getting oil in the air cleaner.
The thought crossed my mind that I had a clogged cat. I found that I could cover the exhaust pipe with my hand and it would never build up pressure. I could feel it coming out but not strong.
Another weird thing is I get fumes and smoke out of the Crankcase vent in the top of the valve cover. I converted it to just a breather because I was getting oil in the air cleaner.
The thought crossed my mind that I had a clogged cat. I found that I could cover the exhaust pipe with my hand and it would never build up pressure. I could feel it coming out but not strong.
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
It must b timing right? I retested the cps and it's back down to .3v AC. I keep coming back to the cps. I guess I'm going to get one from the dealer and see if it works. But the plugs are sparking and the noid light is blinking. But when I dump starting fluid into the intake it won't even hit.
Another weird thing is I get fumes and smoke out of the Crankcase vent in the top of the valve cover. I converted it to just a breather because I was getting oil in the air cleaner.
The thought crossed my mind that I had a clogged cat. I found that I could cover the exhaust pipe with my hand and it would never build up pressure. I could feel it coming out but not strong.
Another weird thing is I get fumes and smoke out of the Crankcase vent in the top of the valve cover. I converted it to just a breather because I was getting oil in the air cleaner.
The thought crossed my mind that I had a clogged cat. I found that I could cover the exhaust pipe with my hand and it would never build up pressure. I could feel it coming out but not strong.


