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Renix issues: stumbling, misfiring....no fun.

Mr. Ninja

NAXJA Forum User
Location
Issaquah
The specs: 1990 XJ, Renix 4.0, 30k miles, manual.

The issue: While driving and NOT heavily accelerating, just cruising along maintaining speed, I've got a wicked misfire/stumble. Seems to do it at any RPM as long as there isn't alot of load on the motor. At Full throttle or even 3/4 throttle while accelerating it pulls fine. It idles fine. It accelerates fine if I'm really accelerating. If i'm just lightly accelerating or maintaing speed is when it stumbles/misfires.

What I know is good/replaced/etc:

O2 sensor is good/new
coil good/new
TPS tested perfect
CPS good/new
plugs good/new NGKs gapped properly
wires/cap/rotor new
fuel pump good/new
fuel filter good/new
fuel pressure reg good/new (pressure tests perfect to spec)
Vaccuum tests good at 16hg/in
Compression tests good at 135 +/- 1 psi all the way across (done with motor cold for about 5-7 cranks)
IAC cleaned, appears to be good
EGR moves smoothly with vac
ECU grounds look good (I also put a few extra 4guage grounds between the block, the frame and the battery)



Another issue JUST started happening while I was doing some diag early today, but it appears my coolant likes to come pissing out of my coolant bottle now with a little pressure(still old style cooling system). It is still a rusty-ish water color, doesn't look like oil or gas in it, smells like coolant. The exhaust has no hints of water/coolant. That combined with the consistant compression numbers makes me think its something other than a headgasket. Also, this could just be cause it was a hot day and I was dicking with it without really driving it around.

SOOOOO...?

Anything I should recheck? or Perhaps I'm not thinking to check?

hasta
 
Double check your EGR Solenoid, mine had a similar issue. When the motor was cold it would idle fine, at part throttle it would stumble until the MAP took over. I failed smog due to high NOX and we traced it down to the EGR Solenoid malfunctioning. It was allowing exhaust gases at the wrong time i.e. you do not want exhaust gas at idle at mid range throttle and you do want them at WOT.
 
Having a 90 you are blessed three times: EGR valve, EGR solenoid, and the Vacuum Transducer.

TEST:

Warm the engine to normal operating temperature.

Operate engine at idle speed.

Check vacuum at solenoid vacuum source.

Disconnect the hose and attach a vacuum gauge to it.

Vacuum should be at 15 inches.

If vacuum is low, check the line for kinks, twists, or a loose connection at vacuum connector on intake manifold.

If vacuum is ok, remove gauge, reconnect the line and proceed to next step.

Check vacuum at solenoid output port.

Disconnect the line and attach a vacuum gauge to output port. Vacuum reading should be 0 at this side of solenoid.

If vacuum reading is 0, leave the gauge connected and proceed to the next step. However, if vacuum is present check solenoid/ECU operation with the DRB-ii tester.

Disconnect electrical connector at solenoid and note vacuum at output port. Vacuum should now be present at output port.

If vacuum is present, proceed to EGR valve test. However, if vacuum is not present, replace the solenoid. Test the EGR valve as follows:

Leave solenoid electrical connector disconnected. Note the engines idle speed.

The engine should idle roughly or stall. If this occurs the valve is ok. If the idle does not change, proceed to next step.

Disconnect hose from the EGR valve and connect a hand vacuum pump to EGR nipple.

Apply a minimum of 12" of vacuum to the valve and note engine idle. If engine now idles rough inspect the vacuum line between the EGR valve and the solenoid.

If the idle did not change, remove the EGR valve and inspect the valve and the exhaust passage in the manifold for blockage, repair as necessary. If no blockage is present replace the EGR valve.

Vacuum Transducer Testing as follows:

Disconnect the transducer vacuum lines and back pressure line. Remove transducer.

Plug transducer output port. Apply 1-2 PSI air pressure to transducer back pressure port. Air pressure can be supplied with a hand operated air pump or compressed air (regulated to correct pressure). Apply a minimum of 12” of vacuum to the input port.

Replace transducer if it will not hold vacuum.
 
where are the transducer and solenoid?

is there a way to effectively just bypass this whole system? seems like alot of nonsense to me...
 
Replace your coolant bottle with one from a mid 90's Mopar, they are made of heavy nylon type plastic and have a real radiator pressure cap on them. On the stumble, check your Manifold air temp sensor, the sensor values are posted on this site somewhere. Worked on mine......
 
where are the transducer and solenoid?

is there a way to effectively just bypass this whole system? seems like alot of nonsense to me...

Place one hand upon the EGR valve.

Follow the vacuum line towards the front of the engine, no more than 4", probably a little less, and there is a round piece of plastic with three nipples, one right, one left, and one on the bottom--that is the vacuum transducer.

Follow the "in" vacuum line (line to EGR is the "out", the line on the bottom is backpressure) to the vacuum solenoid.

Can you bypass the system? Yes. Is it legal to bypass? No. Will it effect how the engine runs or pollute the earth? No. Low compression engines, like our beloved 4.0, really never needed it and the system was eliminated in later years.

My personal preference is to keep all emission components functioning. While the area I live in Oregon does not AT THIS TIME require smog or vehicles inspections, it really is just a matter of time considering that the earth fanatics are in political ascendancy right now.

Washington State (just as bad as California, with Oregon a close third) is trying to pass a "buy and crush" program for older vehicles that can't meet emissions standards. Here in Oregon if the governors of WA or CA stop moving, our beloved governor has to use toilet paper to clean the brown off his face.
 
ok, definately has nothing to do with the EGR system.

any other thoughts?

also, to add, during testing/etc today i took it on a bit of a drive and had no issues with the cooling system....
 
ok, definately has nothing to do with the EGR system.

any other thoughts?

also, to add, during testing/etc today i took it on a bit of a drive and had no issues with the cooling system....

Ok, you said the TPS passed. Did you do the throttle range of motion test for the TPS with an analog meter? You may have a dead spot somewhere in its range, and that could be your problem.

Did you check your cap on the turtle? I bought a chinese bottle with cap and the cap was a POS, bought a new cap at dealer no more problem.
 
TPS passed with a digi meter with a very quick refresh and i went slow, and it doesn't really appear that the issues crop up at a specific throttle position...

I think the cooling system is fine... it appeared to only act up when I had the vac hose going from the firewall side of the intake mani over to the pass side vac canister/4wd vac actuator unplugged for testing purposes....
 
TPS passed with a digi meter with a very quick refresh and i went slow, and it doesn't really appear that the issues crop up at a specific throttle position...

I think the cooling system is fine... it appeared to only act up when I had the vac hose going from the firewall side of the intake mani over to the pass side vac canister/4wd vac actuator unplugged for testing purposes....

did you plug the end of the vacuum line or just disconnected. if disconnected, a vacuum leak can cause problems as the map sensor and egr are both operating off of vacuum.
 
TPS passed with a digi meter with a very quick refresh and i went slow, and it doesn't really appear that the issues crop up at a specific throttle position...

I think the cooling system is fine... it appeared to only act up when I had the vac hose going from the firewall side of the intake mani over to the pass side vac canister/4wd vac actuator unplugged for testing purposes....

Yeah, the problem with the digital meter is the buffering, it will mask bad spots. A $4 analog is the only real check for dead spots. This has been covered many times on this forum.
 
retested with analog meter and there doesn't appear to be any bad spots in the TPS...

and yes, when i disco vac stuff to diag i always plug the van hole....

any other thoughts?
 
I have the same exact symptoms on my 96 and its driving me crazy.
There HAS to be someone thats had the same exact problem and knows the fix.

Lots of ideas...but nothing seems to work
 
I have the same exact symptoms on my 96 and its driving me crazy.
There HAS to be someone thats had the same exact problem and knows the fix.

Lots of ideas...but nothing seems to work

I think his problem is EGR related, but I think your 96 doesn't have an EGR system.
 
i already made a block off plate for the EGR when it was first mentioned and all the different things that could be wrong, figured easier to just build a block off plate.

its pretty frustrating cause i don't have much time to work on it right now, and everytime i go to work on it, i end up spending most of the time catching myself back up on all the things i've done so far....

:-/
 
i already made a block off plate for the EGR when it was first mentioned and all the different things that could be wrong, figured easier to just build a block off plate.

its pretty frustrating cause i don't have much time to work on it right now, and everytime i go to work on it, i end up spending most of the time catching myself back up on all the things i've done so far....

:-/

I'm stumped. You have tested/replaced most of the usual suspects.

Maybe you could take it on a part-throttle extended cruise so that the misfire/stumble is fairly steady, then pull over shut off the engine and pull plugs to try and isolate the problem to a particular cylinder(s). If all the plugs are the same then it is a rolling problem that effects all 6.

There is a good website with diagnostic info on sensors: http://www.lunghd.com/

I don't remember if you tested the MAT and MAP sensors, but not sure if they could give you the symptoms you have.
 
I'm stumped. You have tested/replaced most of the usual suspects.

There is a good website with diagnostic info on sensors: http://www.lunghd.com/

I don't remember if you tested the MAT and MAP sensors, but not sure if they could give you the symptoms you have.
^quoted for link and MAP suggestion^


Did you ever figure out the cause problem? I'm having the same issues

I don't know for sure if he ever solved it, but you will want to start with the same tests he performed- use the link provided and be sure you get good results for each before movin on. He never tested the MAP that I could tell, but it is definitely a possibility for"engine load related problems."
 
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