Renix Problems & cylinder not powering

Ive got a 88 Xj with 260K on it. It just started to "unfire" on the #2 cylinder
and Im pulling my hair out trying to fix this proble.

A week or so ago I change oil and filter, air filter...ya da ya da. I also degreased and washed down the engine as I have for many many years , of course covering the vitals. The Xj has run like a top for the 20+ years Ive owned it. Took it out for a spin after doing the above stated work noticed that I had a cylinder not firing...not a misfire...a cylinder not firing. The last time I had a issue that closely ressemble this issue it turned out to be the 15+ year coil going bad and after I change the coil out the Xj ran great.

SOoooo. I exchanged the coil and....still had the non firing cylinder.

I put a induction timing light on each of the plug wires and the light flashed on each and all wires. This led me to think that ALL plugs were getting spark. Ive sinced pulled all the plugs and they look great. not wet/oily etc. i also did a compression check and the lowest cylinder was 124 the others were 135 or better. Ive also installed my vacuum gage and the vacuum runs steady as a rock at idle and in a straight and level 60 mph cruise.

I then started to pull the FI connectors to each FI and noticed that when I did the rpm would drop....untill I pulled the connector off the #2 cylinder...no rpm drop.

I then took the #1 FI lead off the #1 FI and got a rpm drop but when I placed it on the #2 FI the rpm picked up. THis led me to think that the #2 FI is working correctly. Ive since changed the Renix FI to Ford FI thinking that perhaps the Renix FI had fouled internally and would not let gas pass thru it. Really this didnt fix anything. All in all this leads me to think that the #2 FI is working correctly when I place the #1 FI connector onto the #2 FI. Wired this way (#1connector onto #2 FI) is not "firing" at the correct time but the cylinder is still getting fuel and "running" this way

Ive checked voltage at the #2 FI connector and only get approx .8 of a volt on my cheapo anolog meter which is about the same for the other cylinder FIs that I also checked.

I also wired the #2 FI directly to the battery to see if there would be a rpm increase with the FI open all the time but there was not noticable rpm change...

Yet...As I said before if I take #1 FI connector off, the rpm drops but when I put #1 FI connector on #2 FI the rpm increases. Again I think the #2 FI is working injecting fuel into the #2 cylinder although at the "wrong" time but the #2 cylinder still get fuel.

Ive got the OEM factory manual and found that the #2 FI has a green power wire that come from the Renix computer A3 terminal....

BUT when I look at the Renix Service Manual schematic the #2 FI goes to Renix computer terminal B3. Matter of fact the XJ Factory Manual schematic and Renix Service manual have conflicting wiring/terminal info onto the computer

Cylinder Factory Manual Renix Service Manual
#1 B1 B+ (?)
#2 A3 B3
#3 A1 A1
#4 A4 A3
#5 B2 A2
#6 A2 B2

Any ideas? I would think that if I powered the #2 FI directly to the battery it would open and dump anough fuel into the #2 cylinder and I'ld get a rpm increase...but I dont.

HELP please Im going bald.

I would try replacing the # 2 spark plug, perhaps with a known working plug from another cylinder.

Then try swapping the #1 and # 2 injectors, if spark plug is not the problem. Note that the plug could be shorted internally, grounding out with no proper spark at the tip.

IF those 2 fail you may be one of the few with a bad firing circuit in the Renix computer. WE know of 2 or 3 priors. One was from eastern Europe earlier this year, and he fixed his with a $1 chip. Details are in this forum.
Lastly it could be a bad wire, lead from the ECU to the FI.

Ecomike said:

I would try replacing the # 2 spark plug, perhaps with a known working plug from another cylinder.

Then try swapping the #1 and # 2 injectors, if spark plug is not the problem. Note that the plug could be shorted internally, grounding out with no proper spark at the tip.

IF those 2 fail you may be one of the few with a bad firing circuit in the Renix computer. WE know of 2 or 3 priors. One was from eastern Europe earlier this year, and he fixed his with a $1 chip. Details are in this forum.
Lastly it could be a bad wire, lead from the ECU to the FI.

Click to expand...

The fix was posted, as I recall, by Mr_W from Czechoslovakia. That may help with your searching.

Just to verify, have you checked the #2 injector signal using a "noid light?" You should be able to pick one up for a few bucks at any well-stocked local.

Thanks fellows for the quick replies.

I previously swapped #2 and #3 spark plug...made no difference.

Using my meter I checked continuity for the #2 FI connector (just the green wire) to the ECU and got continuity. I also checked continuity of the green wire to ground and (for a short) and got no reading on the meter...no short. I checked the large conector on the firewall. Its contacts are clean.

What about the difference I listed in the wiring contacts between the Factory Manual Wiring schematic and the Renix Service Wiring Schematic?

Could I get someone with a Renix engine to check what color "power" wire goes to each of their FIs?

Thanks again. I'll look up Mr_W

PTF18,

I assume you checked the FI wire colors to make sure the FI are firing in the proper sequence?

Best regards,

CJR

CJR; My #2 FI has a green wire and a black wire going to it. THis matches my Factory Manual schematic BUT the Renix Service Manual (Im at work and dont have it in front of me) shows a couple cylinders going to different contacts on the ECU

The Renix Schematic is a pdf and is hard to see so maybe Im misreading it.

5-90: I read Mr_W post.......gee you guys lost me....well sort of..... It sounds like the problem I have though. He apparently had a cylinder (#4) that wasnt "firing" its FI.

Im confused by what voltage the FIs need to "fire". 12 VDC I think is correct. If so why dont I "hear" a rpm change when I "hot wire" the #2 FI itself to my 12 VDC battery?

Again if I pull the #1 FI connector off #1 I get (hear) a rpm drop (as I would expect)....and if I place the #1 FI connector onto the #2 FI I get a rpm increase which again leads me to believe that the #2 cylinder is working correctly but its not getting any fuel from the non "firing" #2 FI electrical circuit.

Thanks for the help.....Now I found out My banks ATM machine sucked up my paycheck and then broke down.....cant wait till Friday.

I don't think it's as complicated as it seems. Swap the offending injector and see if the problem persists at the new location - or the same hole keeps it up. You have then isolated the problem - its the injector itself, the wiring, or the computer.

Until you isolate the offender, you haven't finished diagnosis.

It could simply be the wiring, or the injector is either gunked up or weak and won't flow sufficient fuel - which could explain the rpm differences.

TiRod: Did the swap thing already. I took the #1 FI wiring connector off #1 FI. The rpm dropped. I took the #2 FI wiring connecto off #2 FI . No rpm drop. I placed the #1 FI wiring onto the #2 FI. Had a rpm inrease. Put the #2 FI wiring connector on the #1 FI. No rpm inrease. Leads me to believe that the #2 FI electrical system is a issue.

For 87-90 4.0L engines, the color code for the wiring to the fuel injectors is as follows:

#1: Light Blue./Black
#2: Light Green/Black
#3: Tan/Black
#4: Yellow/Black
#5: White./Black
#6: Brown/Black

Hope this helps.

Best regards,

CJR

CJR: Thank you

Somebody correct me if I'm wrong, but I recall warnings against hooking up an injector directly to 12V. Can burn them out. You are going the right way by checking the wires for continuity to the ECU. You could also check for that same 0.8V at the ECU that you got at the injectors.

Located a set of NOID LIGHTs at a local auto parts store to rent. Got home. pulled the #2 FI electrical connector off the #2 FI and installed the Noid light. Started up the engine and.....NO FLASHING NOID LIGHT!!!!

Tried the remaining cylinders and they ALL flashed.

Something is amiss with the #2 FI electical system.

Ideas? I've check the wiring till Im scraped, burned and twisted around in different positions......I dont think its a wiring issue.
Could it be what Mr_W found ???? inside the ECU?

ptf18 said:

Located a set of NOID LIGHTs at a local auto parts store to rent. Got home. pulled the #2 FI electrical connector off the #2 FI and installed the Noid light. Started up the engine and.....NO FLASHING NOID LIGHT!!!!

Tried the remaining cylinders and they ALL flashed.

Something is amiss with the #2 FI electical system.

Ideas? I've check the wiring till Im scraped, burned and twisted around in different positions......I dont think its a wiring issue.
Could it be what Mr_W found ???? inside the ECU?

Click to expand...

Check your PM box...

It's either the wiring or the ECU. It sounds like you traced all the wiring and checked continuity.

I have the EXACT problem on my 96 with cyl #1 Its driving me crazy too
idles like crap but off of idle it runs great.
But on mine the noid light blinks just fine on all cylinders
I did the same Ford FI swap thinking a few injectors could be junk. NO fix either
Im right there with you on pulling your hair out

Bobby: I beleive that your FI system is the OBD 1 type. Whatever that worth.

ptf18 said:

Bobby: I beleive that your FI system is the OBD 1 type. Whatever that worth.

Click to expand...

No its OBD2. its a 96 and everything 96 and up is standardized to OBD2

ptf18,
Sounds like the ground wire (Ground is black I think?), at FI#@ is bad. Try hot wiring the ground.
BUT,

I am not sure if the FI is fired by grounding the FI or by feeding a 12 ( 12V-?) volt pulse to the injector. 5-90 might recall.

The thread by the Chec guy does discuss the ground and voltage!

I have tested FI's with a 9 volt battery a number of times with no problem.

Bobby@Bullydog said:

I have the EXACT problem on my 96 with cyl #1 Its driving me crazy too
idles like crap but off of idle it runs great.
But on mine the noid light blinks just fine on all cylinders
I did the same Ford FI swap thinking a few injectors could be junk. NO fix either
Im right there with you on pulling your hair out

Click to expand...

Have you check compression on that cyl, and the spark and spark plug?