89 4.0 miss, runs rough, need ideas!

I need help diagnosing an engine miss, rough idle....

Ok I just test drove an 89 Renix, 2 WD, 112,000 original miles, that I am planning to buy tomorrow. It's a jewel! But the owner says the local shell gas station's greek mechanic checked it out and says the #5 cylinder is shot. I think blown was the word he used, but this is second hand, so who knows.

I test drove it, and I took it to WOT for a few seconds, from 5 mph to say 20 mph, with no problem!!!!!

At ilde, or cruising, It acts like its running on 4 or 5 cylinders. The Exhaust system Cat converter and muffler and exhaust pipe are already new.
The CCV system is working perfectly, air filter is new, I checked the rotor and cap, they were OK, the spark plugs are new, and were changed just 9,000 miles ago and again 10 miles ago.

The worst spark plug had a thick (1/8") light brown deposit on the electrode after 9,000 miles. The second worst looked OK to me, not great, but a thin layer of light brown deposit, not bad like the worst one. Unfortunately the owner did not mark or track the cylinder the plugs came out of. No oil on the plugs at all.

TPS responds OK from idle to WOT in first gear. I did not take it over 25 mph, and only drove it one block. Tranny feels solid. THis Jeep looks like it was parked in an air conditioned garage for 18 years, and barely driven. But I did see some signs of some sludge under the valve cover area. Oh, and it has no overheating problems, it still has the closed Renix cooling system with about 1-2 year old standard Renix poly bottle with cap, and the AC was working while I ran tests on the engine for about 15 minutes. I tried some obvious simple stuff like cleaning the battery cables while I was checking it out. I found a disconnected EGR vacuum line to the EGR solenoid, and reconnected it, but had no effect. The EGR looked new.

O2 sensor is reportedly the orignal. It just passed the fairly strict Houston, Tx emissions tests but only after getting the new muffler and new cat, and just before the rough idle, engine miss started up.

I am thinking it might be a leaking injector flooding #5. OH, I forgot to mention I could smell raw fuel out the exhaust the first few minutes he ran it. The miss settles down at high rpms, it is still there, but much less noticable at 3,000 rpm, and quite noticable at idle. None of the injectors are leaking externally at all! But, the body color was black on three injectors, and silver on the other three, telling me some of the injectors have been swapped out by the original owner at some point.

He is having dash gauge problems, in particular he said the digital clock has been rapidly fadding from brite to normal (night to day view) , since his engine problem started. I also noticed the Voltmeter was reading fairly low, like in the 8 to 10 volt range, but I did not have time to investigate that further. I should have thrown my volt meter on it, but the owner was short on time and running late for an apt. I also forgot to check the oil dipstick, but he said he had just changed the oil and filter.

Ideas???????

I think a dry/wet compression test, along with checking manifold vacuum will tell you more than anything.

Leak-down at the injector...I like that idea. Check the fuel pressure at the rail after shut-down. I think you should be holding around 20 lbs., but that was a different thread.

I would have expected to see black soot on the plug that was in the dead cyl.
If the injector is leaking down and causing it to drop a cyl. throughout the RPM, it should have carbon fouled the plug. I would look at an injector that's partially plugged up with varnish, as the tan/brownish deposits sound like a lean misfire. As for the gas smell, on cold start the Renix computer richens the mixture a bunch (almost twice the norm) to ensure enough fuel is available at start. It could be residual fuel from start up, or the O2 sensor could be reading the lean exhaust from the fouled injector and telling the ECU to extend the pulse width (time the injectors are open) to compensate for one bad injector. The result would be extra gas in the other 5 cyl.

It sounds as though you've found a nice toy at a great price-- I'd pay the man, drive it home and start tinkering-- it passed emissions recently, so whatever it is shouldn't be too horrible!

--Shorty

A good place to check voltage is at the large yellow wire at the ignition module. Check it both running an then again motor stopped with the ignition in run.
Other than the normal stuff, a couple of things that can cause a miss are a vacuum leak. Too much air on a cylinder or two can cause a miss or rough idle.
Like you mentioned low primary ignition voltage.
And the ignition coil to cap plug wire. Renix seems to be finicky about the ohm reading of the coil to cap wire. They can test good and still cause problems.
A lot of things can go wrong with plug wires, even new ones. They have a tendency not to seat all the way on the plug. The wire sometimes separates from the electrode when pulled by the cable instead of the boot. Excessive resistance is always a problem.
The cap is always something to look closely at, carbon dust causing periodic cross fires, usually in conjunction with high resistance plug wires.
Like mentioned a compression test is always smart. And a vacuum test, to check mostly for a gauge needle that wags excessively.

Fuel filter ;-)
Had the same problems with a 3.0 6-cyl Ford Sierra sedan.... and after swapping air, oil filters, plugs and plug wires, cap and rotor and condensor and coil (!) a very old and wise mechanic in England, set it straight. He changed it out right there on the road, and no furthe problem thereafter. About $10.00

From what I saw, I doubt this one is a fuel delivery problem or spark problem, but I will check the plug wires further.

It ran reasonably well at 3000 plus RPM and at WOT. Miss was most noticable at idle, seems to settle down a lot under heavy load.

I have not ruled out the EGR.

I have ruled out a major vacuum leak for now.

There was absolutely no sign of major crankase blow by, but I did only disconnected the small CCV line and the oil filler cap, not the larger air filter CCV line, so I need to retest that as that large line would have been sucking some air from the crancase with the other two openings open to atm.

Running a vacuum gauge test will be real easy and should be VERY revealing, so I will try that next.

I have an 87 Renix that ran extreemly rich for 2 years while I debugged it, so I am familiar with the rich exhaust fumes from a Renix that is running rich from not having a working O2 sensor. This one had 3 or 4 times more raw fuel in the exhaust, telling me one or more injectors had to be leaking the first few minutes. What was interesting is the odor abated after several minutes or so, I think, I did not time it, could have been just 30 to 60 seconds before the odor abated.

If it does have actual low compression on the #5 cyl. like 90 psi, but is not completely shot, like a bad valve in the head with no compression, I am planning to try the engine oil additive know as "Restore" which uses sub-micron colloidal silver/copper/lead particles in the formula that claim to plate out on the walls of low compression cylinders to "restore" compression to that cylinder. Will try it just out of curiousty, as the cost is under $10. I am hoping the cylinder, if that is the problem, has not been permanently worn out of tolerance, and just needs a new injector and oil on the cylider walls to get it back in service.

I do have a few questions!

1) If it is low compression on cyl #5, do these symptoms match, i.e. very rough idle that smooths out 95% at say 3000 rpm? The miss is not very noticable at 3000 rpm.

2) What does the thick dry brown deposit on the one spark plug mean?

3) What color is the spark plug deposit for very small coolant leaks into the combustion chamber.

Well I bought it, so whatever is wrong with it, it's my problem now.

I already found two spark plug wires that were not properly connected to the spark plug, the metal clip in the boot was not snapped on the end of the spark plug. I reconnected all the spark plug wires, and it helped the idle smooth some.

I took it up on the freeway, ran it up to 70 mph in third, and it ran pretty smooth, in fact if I had not been looking for signs of a miss, or bad cylinder, I would have said it was running normally at that point.

I think it is running smother at idle, and at low cruising rpms when it is hot, so I have the O2 sensor (internal O2 sensor heater) on my check list, but I know of 3 injectors that I can disconnect that seem to have little effect on the idle, while cylinder #2 when disconnected nearly kills the idle. #4 injector does not sound like its clicking (using a stethoscope) # 5 is getting spark, and the injector is clicking, but disconnecting the electric to the #5 injector just barely affects the idle, but not nearly as much #2 does.

TPS and TPS voltage are good, and in spec. Sensor and engine ground to the battery is 2.5 ohms, not perfect, but not bad enough to cause the engine miss. Battery voltage and alternator with AC on high and head lights on checks out OK so the battery and alternator are good. Unknown, Low voltage problem at the dash voltage gauge and radio, extent of problem unknown at this point, but AC fan works and ac works fine.

Starter makes a weird cranking sound. I get two normal sounds of cranking followed by a third rapid, long duration sounding whine, then the sound pattern repeats itself. I cranked it at WOT, to kill the fuel supply, and cranked it for 30 seconds, and the cranking sound pattern did not change. Not sure if it is the stater, the bendix/relay, battery, or the engine causing this odd sound, but multiple low compression cylinders, 2 good, one bad, 2 good, one bad, = 6 cyl, has been suggested by a daily auto mechanic friend of mine that heard it last night.

I discovered an unknown overheating problem driving it home last night in bumper to bumper, dead stopped traffic for 30 minutes. Fan Clutch is bad, and the electric fan did not run with the AC on, or with the high temperature coolant (radiator fan switch), so I pulled over cut the wires to the defective radiator fan switch, stripped the ends, twisted the bare ends together, and taped it up so the electric fan is on all the time as long as the ignition switch is on, now. Nice emergency, in the woods repair method that took only a knife and electrical tape to accomplish!

I am going to test and probably replace the 7 mm silicone HV wires. I plan to order a quality set of new flow matched, Five-O fuel injectors, (I am just not too crazy about messing with used injectors).

Oh, I ran a vacuum test yesterday before I found and fixed the 2 disconnected spark plug wires. I only got 16" of vacuum at idle, but the idle seemed very low, like 350 rpm maybe (No tach on the dash, so guessing by the sound as to rpm for now). It had about a l2" rapid oscilation in the vacuum at idle. Inceasing the RPM raised the vacuum to a max of 20" at about 3000 rpm, and rapid decel vacuum maxed out at only 22" of vacuum.

My mechanic friend confirmed what I thought I heard, a small exhaust leak, possibly at the manifold, so I have not ruled out an Intake manifold leak, yet (would be hard to hear due to the exhaust leak noise).

Oil pressure, (with fresh oil and filter using 10W30, done by prior owner at a jiffy lube, just days before he sold it to me) is 44 PSI at cold start, about 32 at cruising speed hot, and 21 psi minimum at hot idle.

O2 sensor may be the original, actual age unknown. Odometer says 125,000 miles, but car fax had it registered in 1996 with 112, 000 miles, so I have reason to suspect the dash gauge was swapped out with a low mileage dash, or else this jeep was stored indoors for nearly 10 years, which is possible considering the paint and interior fabric condition which are excellent, based on the age, it's an 89, Cherokee Pioneer. Oh, and it came with a cool front bumper guard, the $300 cattle guard kind.

Transmission seems to be fine. Seems to still have full throttle power which is encouraging.

Based on this data so far, what do you all think is the real problem?

Oh, the EGR looks new, and disconnecting the vacuum line to the EGR has no effect on the idle. I have not tried other EGR tests yet.

Also, the idle speed and miss did not change when I pulled vacuum line to the fuel pressure regulator on the fuel rail! As I recall it should affect the idle! Of course the injector problems could be masking it.

Also, I still smell excess fuel out the exhaust at idle, after a long hard drive, inspite of a new Cat and muffler just installed 12 weeks ago. It passed the Texas Emissions test in Harris county, Tx 12 weeks ago just after getting the new Cat and muffler. I am running fuel injector cleaner with the gas right now. I plan to test the O2 sensor to see what its doing soon. It should be interesting.

Don't know how much testing I will get done this weekend, if any. Getting ready for H. Dean now in case it comes for an uninvited visit next week.

So does part of this sound like burned or damaged valves, worn, gas washed cylinders from bad injectors, or an intake manifold leak maybe coupled to an exhaust manifold leak, or maybe even a bad EGR, or some combo of these. It does seem to have at least one non working (no clicking sound) injector, that could be stuck open!?????

I think if you had a bad injector, the miss would never really go away. You can, while idling, pull the connector off each injector (one at a time) and see if the miss worsens (it should). Then reconnect it and it should smooth out. If you find one that makes no difference, then there's something wrong with the injector, the connector or the signal to it.

My Bosch starter makes a whine whenever I start. After I return the key back to the run position and the bendix disengages, it sounds like my starter keeps freewheeling until it finally spins down.

Yeah, I am not sure what to make of the starter noise yet. I do plan to run a battery voltage test on the starter shortly to see if it is a bad battery as far as cranking amps are concerned.

I already ran the injector tests......One of the injectors (#4) does not make a clicking sound tested with a stethescope at idle, a noid light test confirmed the voltage signal to the suspect injectors, and the other suspect injector does click, but does not affect the idle much whether connected or not (almost imperceptable change on the clicking suspect injector, and no change on the non clicking injector). Injector # 3 makes a huge, noticable change in the idle when disconnected, in fact the engine nearly dies when I disconnect the #3 injector control signal wires.

I should add that it starts in under 5 seconds of cranking, but sounds like it is cranking slowly, slower than my other 4.0 cranks.

Saudade said:

I think if you had a bad injector, the miss would never really go away. You can, while idling, pull the connector off each injector (one at a time) and see if the miss worsens (it should). Then reconnect it and it should smooth out. If you find one that makes no difference, then there's something wrong with the injector, the connector or the signal to it.

My Bosch starter makes a whine whenever I start. After I return the key back to the run position and the bendix disengages, it sounds like my starter keeps freewheeling until it finally spins down.

Click to expand...

Battery is reading a steady, solid 10.64 volts during 20 seconds of starter cranking, and that is while the electric cooling fan is still running (due to yesterdays emergency bypass). So the battery is OK. I am hopping the starter noise is not from engine problems.

I have been reading my archives on engine vacuum tests and they sound encouraging. I retested all six fuel injectors. #1, #2, #3, and #6 injectors are obviously working from the test (Tested by pulling the injector wires off the injector, and reinstalling them to look for noticable idle changes). Injector #4 is not clicking and seems to be totally dead. Injector #5 had no effect on cold idle, though it had a very small, tiny effect at warm idle last night and it clicks, so it must be partly, or mostly clogged.

I runs pretty good for two bad injectors!

Also, I watched the EGR valve (shaft) movement at idle, at 2500 rpm and during rapid accel and decel, and it seems to working properly. So far the EGR does not seem to be part of the current problem.

What does a compression check indicate? You should know that injector connectors will cause intermittent miss conditions. In my 89 design the connectors hold water and corrode causing a bad electrical connection. Usually worse when cold and at idle.

Overheating - put a new radiator in there. Mileage doesn't matter as much as years when it comes to radiator capacity. I know you'll do the fan, clutch, thermostat, etc. When all that fails to control the heat, put a rad in or just do it from the start and save yourself a lot of grief.

Like I said in the beginning - do a compression check and leakdown test to qualify the engine mechanical condition.

Renix O2 is easy, just look for strong rapid switching voltage with a meter when hot.

What does the compression test show?

Have not not done a compression test yet, don't know when I will get around to that, but I have run an engine Vacuum test, which in my opinion (based on other write ups) can be, and in this case is even more revealing than a compression test would be. So far the engine Vacuum at the intake manifold test shows no loss of compression, shows no intake leaks and shows a possible bad injector, which I have confirmed with the 2 injector tests that show injector number 4 to be dead, and number 5 to be nearly dead, or severly clogged. Planning to run Seafoam in the gas tank and carburator aerosol cleaner through the throttle body and IAC port while I try to decide if I can rig up a way to test the 18 old injectors I have laying around (I know some of them leak externally through the case but I don't which ones are which, and do not know which ones might be partly clogged, so I need to come up with a diesel fuel pump and plumbing rig to test them under pressure so I can find 2 good working, non-leaking ones to replace #4 & 5 inectors for further tests while waiting on new injectors. With two bad injectors, it is no surprise that it has an idle miss and shake.

Not much sense in testing the O2 sensor output with 2 bad injectors at this point but I will probably test the O2 sensor heater and heater circuit voltage shortly. I am going to put new plug wires, cap and rotor, on it today.

I don't think the radiator on this one is bad yet. It takes a good while for it to overheat, and it stays pretty much at 210 F with the electric Fan on all the time and AC off in 95 Ambient, on the freeway and in stop & go traffic. The mechanical fan clutch free wheels at 210 F so it is shot, useless.

XJXJ said:

What does a compression check indicate? You should know that injector connectors will cause intermittent miss conditions. In my 89 design the connectors hold water and corrode causing a bad electrical connection. Usually worse when cold and at idle.

Overheating - put a new radiator in there. Mileage doesn't matter as much as years when it comes to radiator capacity. I know you'll do the fan, clutch, thermostat, etc. When all that fails to control the heat, put a rad in or just do it from the start and save yourself a lot of grief.

Like I said in the beginning - do a compression check and leakdown test to qualify the engine mechanical condition.

Renix O2 is easy, just look for strong rapid switching voltage with a meter when hot.

What does the compression test show?

Click to expand...

Update: I replaced the spark plug wires, but no joy. Still no power out of cylinders #4 & #5. So I tested the fuel injectors and #3,4 & 5 all ohmed out 17.6 ohms. So I pulled the fuel rail and injectors, then I turned on the ignition, but did not start the engine. I cycled it several times to make sure I had fuel pressure at the injectors (I had pulled injector #5 earlier to inspect it closer, and had drained the fuel rail in the process). All six injectors are totally leak free. No drips from the ends of any of them, which is GOOD news!

So I am hoping it is just stuck, junked up, trash in the injector tip, no gas getting through the injector problems with #4 & #5, and not a compression problem with those 2 cylinders.

Oh, and I drove it again earlier today, and it has one hell of lot of power for just a four banger!:roflmao:

Have you tried swapping injectors?

I do have a few questions!

1) If it is low compression on cyl #5, do these symptoms match, i.e. very rough idle that smooths out 95% at say 3000 rpm? The miss is not very noticable at 3000 rpm.

A: I suspect a mechanical failure. Your Vacuum from what you describe, seems it may be a valve spring. Just to verify the vac reading is erratic at idle and gets worse as you open the throttle? Depending exaclty what reading you get it just amy be that.

2) What does the thick dry brown deposit on the one spark plug mean?

A: The plugs that are in there now are too hot. Try switching to a cooler plug

3) What color is the spark plug deposit for very small coolant leaks into the combustion chamber.

A: Everytime I've torn down an engine which was ran with coolant in the combustion chamber the plugs look really clean as though the were steam cleaned

If you do a compression test and cylinder leakdown test and everything looks normal go after the valve springs. Especially if the leak down is OK. As long as the compresion in all holes is within 20% of eachother your compression is OK. Hope this helps. Is their any engine noise?

John

" I have two used injectors I am going to swap out for #4 & #5 next, which reminds me,

Does anyone recognise these numbers?

Tomco Inc., Rotary disk, 26, 3508, D38008A?

These injectors came off a Jeep 4.0 but I am wondering if they are the proper size?
They look fairly new."

Well I got an answer from Tomco:

"This s our #15505 and is rated 14-16 ohms, 18.13
pounds per hour at 36.25 PSI."

I am going to try them today, weather :sunshine: permitting.

Well it is starting to look discouraging. I swapped the injectors. The ones I pulled tested as OK. I used a 9 volt dc batery, and the injectors are opening and closing. I can blow through them (pushing a trace of remaining fuel out) with them powered open, and I could not blow through them when poered dwon (no power to them). So It looks like I had fuel and spark, put no power output, which means either valve, valve spring or cylinder compression (piston, piston ring, cylinder wall problems).

I will check the injector wires one last time tomarrow to make sure they were getting a signal to the #4 & #5 injectors.

Based on my last post(s) of test results, I am thinking the next thing I should do is to pull the valve cover and do a visual inspection of the springs, valves, etc. and hope the problem is on top before pulling the head?

Any suggestions out there 4.0 land?

I am leaning towards (praying for) a bad, weak, or damaged exhaust valve spring on #4 and #5. I have not doupt there is a compression problem in #4 and #5 now. It would explain all the test results and symptoms so far.

I did find a pair of custom vacuum pipe 'T's (1/4" ID) that tied the front valve cover vent fitting straight to the intake manifold with a 1/4" ID line, (that could have been added by the second prior owner reportedly a mechanic) (and I need to test this theory next) to increase the flow in the CCV vent line system to remove a large amount of blow by gasses and keep oil from getting blown into the air filter. The way it was plumbed might have reduced intake vacuum at idle a little too.

I have restored the OEM CCV vent line set up, so if it was there to remove a large amount of blow by gasses I might see the blow by at the valve cover in my next test. That would hint toward bad piston rings, cylinder wear, or a bad intake valves on #4 & #5 if there is a lot of blow by.

A friend of mine suggested to me the head gasket could be bad between the #4 & #5 cylinders! Which he says would fit the symptoms.:bawl:.

So my guestion is would that really fit the symptoms, and would'nt it cause intake & exhaust problems with the other 4 cylinders and keep the engine from running well at 3000 rpm? Also would'nt that cause a large vacuum drop or larger oscilation span than the 14.5 to 15.5 inches of vacuum, rapid oscilation that I have at idle?