1989 4.0 Cherokee starting slow
11-16-2011, 07:53 PM
#1
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Year: 1989
Model: Cherokee
Engine: 4.0
1989 4.0 Cherokee starting slow
I've owned 3 cherokees, and all of them started very fast. a few cranks, or even 1 1/2 a crank, and fired right up. However, this 1989 Cherokee seems to crank over too many times before firing. I bought it with a bad fuel pump, replaced it, and it's run fine ever since, except for the slow to start issue. I don't mean that the battery turns the engine over slowly, because it doesn't. Engine turns over quickly. the fuel pump I can hear charging up, and everything is a go. The previous owner said it always fired up quickly. I've checked the plugs, and cap and rotor, so that part looks fine. What's next? fuel rail pressure and/or bleed down? I just am not sure.
11-16-2011, 07:56 PM
#2
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Year: 1996
Model: Cherokee
Engine: 4.0
I was under the impression that the Renix engines were all slow to start. Were the other cherokees you owned a little bit newer without the renix?
11-16-2011, 07:59 PM
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Year: 1989
Model: Cherokee
Engine: 4.0
actually, 1 was also an 89. But yeah, the other ones were newer. The other 89 fired right up similar to the newer ones though. I thought about that renix issue, but compared to my other one, was kinda confused.
11-16-2011, 08:29 PM
#4
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5-10 seconds to start is normal for a renix, they have a couple more things they look for before they start, unlike the HOs.
My old 89, 24*:
My new 89, ~60*:
My old 89, 24*:
Last edited by 89Laredo; 11-16-2011 at 09:02 PM.
11-16-2011, 08:57 PM
#5
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Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Check your CPS output voltage. It might be low.
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.
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 3.5 range 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 it’s mounting holes with the first drill bit that just won’t fit through the original holes. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.
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.
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 3.5 range 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 it’s mounting holes with the first drill bit that just won’t fit through the original holes. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.
11-16-2011, 10:19 PM
#6
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Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
Great info guys. Mine too takes a few revs to fire. Cruiser, you gave me a chance to post this nifty pic of where the harness to my CPS sort of dissolved some. Here I've cut away gummy swollen "stuff". I slathered this in RTV before the manifolds when back on.
11-17-2011, 04:53 AM
#7
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Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Just so you all don't get your hopes up I thought I'd let you know that this long cranking time will never be eliminated, only improved. It's the nature of the beast.
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11-17-2011, 07:21 AM
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Year: 1989
Model: Cherokee
Engine: 4.0 liter 6 cylinder
that answers alot about my 89, thats the first thing i noticed when i got it, it takes about 8 to10 seconds to fire up, but runs good so i deal with it.
11-17-2011, 09:24 AM
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Year: 90,84
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John, that's sort of long. Try turning the ign on for a few secs then of and on again a few times, then start it. You might have a bad check valve or fuel getting past an injector or somewhere else. If it starts quicker that might tell you.
11-17-2011, 08:11 PM
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Year: 1989
Model: Cherokee
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thanks for all the info! I'm going to check into the things mentioned. Love the jeep, but was just a little worried about the 'slow' start...
11-17-2011, 08:13 PM
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Year: 1990
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11-17-2011, 08:39 PM
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Year: 1989
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11-17-2011, 09:10 PM
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Year: 1990
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