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  #1  
Old February 5th, 2020, 05:33
szachmat szachmat is offline
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Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

Hello,


I'm Mat, im from Poland and I have a problem with my Jeep Cherokee XJ 4.0 1990, renix.

It's on 31 inch tires and 3 inch lift and i have like 16 seconds for 0-60mph, it's hard to pass 75mph, and 85 mph is impossible to reach, and with normal driving on the streets i get about ~7 mpg. Highway cruising gives me 9mpg.






I have replaced O2 sensor, TPS sensor, MAP sensor, engine timing chain and sprockets, distributor cap, spark plugs, wires, ignition coil (all brand new), and i tried new ignition module (got used one from an old renault).

I have checked temperature sensors (engine coolant and air temperature), and CPS they are fine.


I have checked my timing with a strobe lamp (with regulation) and its about 52 degrees advanced. No matter what i do with a distributor, or any other thing its always on 52~degrees. I tried to set a distributor in other position but it doesnt change anything, jeep starts but its still about 50 degrees advanced.


I order complete new distributor and CPS sensor but i need to wait 2 to 4 weeks till it will arrive from US, because its impossible to get one in Poland, but im not sure if it can help....


Im running out of ideas and my jeep still isn't working as i would like.
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  #2  
Old February 5th, 2020, 05:45
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old_man old_man is offline
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

Timing is regulated by the ECU (computer) and the CPS (crank shaft position sensor)

Unless the transmission has been off and the flywheel/flexplate installed wrong (hard to do due to bolt spacing) I would say the problem has to be the ECU.

The CPS either reads the notches on the flywheel or doesn't. It either runs or it doesn't. The notches are in a particular order and the computer looks for this order before supplying the spark. The odds of the CPS causing this are one in a million.
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  #3  
Old February 5th, 2020, 05:50
CJR CJR is offline
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

My suggestion to you is first visit Cruiser54's website and read what he has written. Randomly throwing parts at your Renix XJ is not going to solve your problem.

Best regards,

CJR
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  #4  
Old February 5th, 2020, 05:52
szachmat szachmat is offline
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

Thank you for fast replay!


You are talking about ECU under main console inside car?
I always heared that its regulated by ignition module (the one with coil on it)
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  #5  
Old February 5th, 2020, 06:13
szachmat szachmat is offline
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

@CJR, thanks for tip, but i have changed all those parts because my jeep had other problems too, it eliminated most of them.
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  #6  
Old February 5th, 2020, 07:15
RCP Phx RCP Phx is offline
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

Quote:
Originally Posted by szachmat View Post
I have checked my timing with a strobe lamp (with regulation) and its about 52 degrees advanced. No matter what i do with a distributor, or any other thing its always on 52~degrees. I tried to set a distributor in other position but it doesn't change anything, jeep starts but its still about 50 degrees advanced.
This makes no sense, as in it's basically impossible!
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  #7  
Old February 5th, 2020, 09:38
Black1990jeep Black1990jeep is offline
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

I too have a 1990, sluggish performance, finally figured it out, the catalyst was breaking down and clogging. Test by removing the cat. or put a vacuum gage on the intake and see what you get. I had to diagnois mine on a road trip, so I had no vacuum gage, so I unbolted the cat. , a vacuum gage will also give clues to valve operation problems. also check for intake leaks, that is a quick and easy test, and will eliminate leaks as a problem if it passes.
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  #8  
Old February 5th, 2020, 09:45
szachmat szachmat is offline
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

Cat is cut out
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  #9  
Old February 6th, 2020, 05:19
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

www.cruiser54.com

Tips 1,3,4, and 5. Then do the distributor indexing.
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  #10  
Old February 7th, 2020, 23:37
szachmat szachmat is offline
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

Guys, yesterday i tried to clean some grounds, connectors and tried few things, and now i', totaly confused....

So i unplugged spark plug on a 1st cylinder, to check if TDC really matches with a mark on vibration damper, and.... COMPLETELY NOT.
So i put engine on tdc on 1st cylinder, and re indexed distributor so now it maches #1 tdc as it should, and it changed nothing. Power is still the same ~15-16 sec 0-60mph.
But i found another funny thing. Accidently i didnt plug in my distributor sensor, and jeep started normally. I tried to unplug the distributor on running engine and it makes no changes. It completely doesn't matter if its plugged or not. Then i checked the voltage on connector. According to renix manual i have found it should be ~5 volts. I have 2.91volts. I tried to take new ground from a chassis, and when i do it's then 7.91volts....
Does that mean i need to look for a damaged cables in my instalation?
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  #11  
Old February 8th, 2020, 06:22
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

It is not uncommon on the older vehicles that the rubber in the harmonic balancer degrades and the pulley slips. While that will not really cause the timing to be off, it will make it look like it is.

The old school method to find the real TDC is to put a rod down in the cylinder through the spark plug hole. SLOWLY rotate the crank with a wrench until the piston softly contacts the rod. Then mark a spot on the harmonic damper. Then rotate the crank the other direction until the piston once again hits the rod. Mark that spot on the harmonic balancer. True TDC should be half way between the two marks.
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Last edited by old_man; February 8th, 2020 at 06:25.
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  #12  
Old February 8th, 2020, 07:13
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

Quote:
Originally Posted by old_man View Post
It is not uncommon on the older vehicles that the rubber in the harmonic balancer degrades and the pulley slips. While that will not really cause the timing to be off, it will make it look like it is.

The old school method to find the real TDC is to put a rod down in the cylinder through the spark plug hole. SLOWLY rotate the crank with a wrench until the piston softly contacts the rod. Then mark a spot on the harmonic damper. Then rotate the crank the other direction until the piston once again hits the rod. Mark that spot on the harmonic balancer. True TDC should be half way between the two marks.
You beat me to it!!!
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  #13  
Old February 8th, 2020, 09:39
szachmat szachmat is offline
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

That's how i did it.
But still i don't know what to think about my dristributor and it's voltage.
And why i have so bad mpg and low power.
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  #14  
Old February 8th, 2020, 09:45
lawsoncl lawsoncl is offline
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

Quote:
Originally Posted by szachmat View Post
But i found another funny thing. Accidently i didnt plug in my distributor sensor, and jeep started normally. I tried to unplug the distributor on running engine and it makes no changes.

On the Renix, the distributor sensor is only used to determine which stroke it's on because it can't know that by just looking at the crank sensor. If there is no dist sensor input when it first cranks, the ECU will take a 50-50 guess. I don't think it should have 5-volts to the sensor, but not sure. I doubt the ECM is the issue.



Spitballing a bit... How did the old plugs look? All similar, one significantly cleaner or darker than the rest? I'm just wondering if you've got a leaking or failed injector throwing the O2 sensor off and making all the other cylinder run rich. Does the exhaust smell rich? A set of refurbished 4-hole Bosch sensors are relatively cheap, btw. Do you have power to the O2 sensor heating element? Is it the correct O2 sensor, as the Renix used a different type than HO? Is the vacuum line to the fuel pressure regulator intact, and does the fuel pressure look correct at idle and hold when the ignition is turned off? Pull off the vac line to the fuel regulator and make sure it's not leaking gas into the vac line. Compression numbers look good?



Definitely visit Cruisers site and start walking through all the tips.
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  #15  
Old February 8th, 2020, 09:56
lawsoncl lawsoncl is offline
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Re: Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing

Check the knock sensor too, btw.
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