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  #1  
Old November 27th, 2017, 23:03
camojeep88 camojeep88 is offline
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88 rough idle and no power

i have an 88 xj with 4.0. I've replaced pretty much everything and still no luck. new cap, rotor,distributor, cps, tps, cat, plugs, wires, coil, icm, injectors, fpr, cleaned throttle body, iac, grounds, I added a ground from battery to body. fuel pressure is 31 at idle and 39 with no vacuum, did vacuum test and at idle is at 16. I'm lost as to what is wrong. it is misfiring on cylinder 6 and when cold I get no throttle response and very poor power. it's hard to get it to 55 and usually takes me holding the pedal to the floor. sometimes it idles great but most the time it just runs rough. some please help
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Old November 28th, 2017, 06:07
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Re: 88 rough idle and no power

16 is low vacuum for sea level. Perhaps your EGR valve is sticking open.
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Old November 28th, 2017, 06:42
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Re: 88 rough idle and no power

double check cylinder compression too. have you owned this before it was doing this? or did you just get it?
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Old November 28th, 2017, 12:52
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Re: 88 rough idle and no power

Not positive of desired fuel pressure (don't have manual with me), but I believe pressure should be mid-upper 40's.
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Old November 28th, 2017, 17:46
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Re: 88 rough idle and no power

Verify distributor indexing, spark plug wiring, vacuum leaks, clogged air filter.
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Old November 28th, 2017, 20:41
camojeep88 camojeep88 is offline
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Re: 88 rough idle and no power

I've owned it for a while now but compression is my next rest just gotta find the time to do it. as far as vacuum goes I thought it was low too but I sprayed carb and choke cleaner all over and it doesn't phase it at all
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Old November 28th, 2017, 20:43
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Re: 88 rough idle and no power

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Originally Posted by camojeep88 View Post
I've owned it for a while now but compression is my next rest just gotta find the time to do it. as far as vacuum goes I thought it was low too but I sprayed carb and choke cleaner all over and it doesn't phase it at all
Low vacuum can be caused by many more things than a vacuum leak.............
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Old November 28th, 2017, 20:48
camojeep88 camojeep88 is offline
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Re: 88 rough idle and no power

and from what I remember the fuel pressure on the 80s is 31 at idle and 39 with no vacuum check distributor and it seems ok when it's at tdc the rotor is pointing at the number 1
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Old November 30th, 2017, 22:42
camojeep88 camojeep88 is offline
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Re: 88 rough idle and no power

turns out cylinders 1,3,4 have 100psi of compression and 2,5,6 habe closer to 75. looks like I'm up a creek without a paddle
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Old November 30th, 2017, 23:55
lawsoncl lawsoncl is offline
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Re: 88 rough idle and no power

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Originally Posted by cruiser54 View Post
Low vacuum can be caused by many more things than a vacuum leak.............

Timing chain jump a tooth?
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  #11  
Old December 1st, 2017, 05:45
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Re: 88 rough idle and no power

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Timing chain jump a tooth?

I'm thinking bad compression rings.
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  #12  
Old December 1st, 2017, 10:39
camojeep88 camojeep88 is offline
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Re: 88 rough idle and no power

a friend told me his buddy had a low compression issue and it was a matter of head bolts coming loose just enough for it to cause issues so I figure it's worth having a look but for the most part I'm thinking it's done. no time like the present to start a striker install 🤗
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Old December 1st, 2017, 14:08
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Re: 88 rough idle and no power

Quote:
Originally Posted by camojeep88 View Post
i have an 88 xj with 4.0. I've replaced pretty much everything and still no luck. new cap, rotor,distributor, cps, tps, cat, plugs, wires, coil, icm, injectors, fpr, cleaned throttle body, iac, grounds, I added a ground from battery to body. fuel pressure is 31 at idle and 39 with no vacuum, did vacuum test and at idle is at 16. I'm lost as to what is wrong. it is misfiring on cylinder 6 and when cold I get no throttle response and very poor power. it's hard to get it to 55 and usually takes me holding the pedal to the floor. sometimes it idles great but most the time it just runs rough. some please help
When I had those problems over the years, it was either a loose helical gear on the distributor shaft, a Bad TPS (unusual as it tested good using FSM tests), A bent throttle body actuator rod, A dying ICM under the HV coil, leaking FPR, leaking into the vacuum line, and one you should still check is the Vac line from the throttle body to the MAP sensor, Pull it out and examine every micro inch of it for bad spots!!! Those are most of them LOL. I had one that ran like crap at idle and great at 2000-3000 rpm that had 45 psi in Cyls 3 and 4. The supper thin head gasket between the cylinders was burned through by carbon deposits there that got red hot running lean.

I would recheck the compression, and make sure you had the good o'ring seals on the tester hose threads, and use an air compressor to blow sand out of the spark plug area before removing the plugs. I use brake solvent to dissolve any oil, then blow it out (wear eye protection) so you know the o'ring sealing are is clean!!!! Then re-run the compression tests, also add some oil top side of the pistons first, about a tea spoon.

If the low compression is still there, pull the head to see if the valves, and or head gasket are bad, as that is an easy fix. 16" of vacuum is not the end of the world at sea level. 17" is better.
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Old December 1st, 2017, 14:09
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Re: 88 rough idle and no power

Is the Distributor properly indexed????

Also make sure you have the spark plug wires on the correct cylinders, same for the injectors. Way too easy to swap them to the wrong ones, do not ask me how I know, LOL.

I seriously doubt it is head bolts being loose, burned out head gasket from running too lean with past carbon fouling is very possible.

But it is way too easy to get bad test data by not getting a good seal on the SP threads!!!! Retest and verify!!!
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34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091

Last edited by Ecomike; December 1st, 2017 at 14:15.
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Old December 3rd, 2017, 11:11
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Re: 88 rough idle and no power

Quote:
Originally Posted by Ecomike View Post
Is the Distributor properly indexed????

Also make sure you have the spark plug wires on the correct cylinders, same for the injectors. Way too easy to swap them to the wrong ones, do not ask me how I know, LOL.

I seriously doubt it is head bolts being loose, burned out head gasket from running too lean with past carbon fouling is very possible.

But it is way too easy to get bad test data by not getting a good seal on the SP threads!!!! Retest and verify!!!
X2 on everything.
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