post #1 of Old 07-11-2007, 07:27 AM Thread Starter
smsdway
Registered User
1989 YJ Wrangler 
 
Join Date: Jul 2007
Location: maine
Posts: 5
89 wrangler 4.2 misfire/backfire help

Hopefully someone can help me diagnose this problem:

I have an 89 wrangler 4.2 standard xmission.

It starts OK, but seems to misfire occasionally at idle and sometimes the rpm's will drop to 0 and it will almost stall out. After it warms up and while driving it, the rpm's exhibit the same symptom and it will start backfiring through the exhaust. Sometimes I'll just be cruising along and the power will just drop out like the vehicle has stalled out and this is when the backfiring starts to occur.

Anyone have any ideas? I've browsed through the forums and many seem to point to causes that I do not believe are my problem.

I have replaced the distributor, wires and plugs last year. The plugs still look acceptable.
I tried bypassing the egr valve and that seemed to make it worse. (running rougher at idle)
Looked inside the cat and its not clogged; there was no honeycomb, just some fins attached to the air intake on the side.

Recently put on a new O2 sensor.

Any help would be greatly appreciated. I'm afraid if I take this to the mechanic there gonna start hipshooting this one.

smsdway is offline  
post #2 of Old 07-11-2007, 08:54 AM
Ares
Registered User
 
Ares's Avatar
1988 YJ Wrangler 
 
Join Date: Jun 2006
Location: Ellensburg/Redmond, WA
Posts: 1,363
Check your PCV valve along with the lines attached to it, make sure they are clean. Double check all the vacuum lines on the carb too. Could be a vacuum problem
Ares is offline  
post #3 of Old 07-11-2007, 10:05 AM
giggityjeeper
Registered User
1990 YJ Wrangler 
 
Join Date: May 2007
Location: British Columbia
Posts: 4,022
everyone will tell you to check for vac leaks and yoiu should, this is pretty common cause of problems, chek all vac lines, when you capped off you EGR is it selaed tight, I used a seal and an aluminium plate to cover mine,

while troubleshooting mine I had to chage the dist, that was the major problem, Also I changed my wires only 1 year ago but they were toast already so they needed replaced as well, the cause ofthe missfire and and backfire for me was a bad ECM and number 5 cylinder was not firing even with new wires...

Started with some rust repairs ended in a SOA...

http://www.jeepforum.com/forum/f12/h...-jeep-1050879/

family roll bar swap/upgrade..

http://www.jeepforum.com/forum/f12/f...grade-1054753/

1990 YJ. SOA, OME 36R 3.5" lift springs, OME 5/8 greasable shackles, OTT high steer, Custom cage, team Rush, Posi, 33 TSL swampers
giggityjeeper is offline  
post #4 of Old 07-11-2007, 10:07 AM
giggityjeeper
Registered User
1990 YJ Wrangler 
 
Join Date: May 2007
Location: British Columbia
Posts: 4,022
Quote:
Originally Posted by smsdway
.

It starts OK, but seems to misfire occasionally at idle and sometimes the rpm's will drop to 0 and it will almost stall out. After it warms up and while driving it, the rpm's exhibit the same symptom and it will start backfiring through the exhaust. Sometimes I'll just be cruising along and the power will just drop out like the vehicle has stalled out and this is when the backfiring starts to occur.

.
check the ECM and couble check your wires, the misfirea and backfire on mine changed our thinking to electrical and that is what it was, not a fuel problem or vac leak...

My Ecm was cracked and grounding out on bumps causeing it to miss and backfire...

Started with some rust repairs ended in a SOA...

http://www.jeepforum.com/forum/f12/h...-jeep-1050879/

family roll bar swap/upgrade..

http://www.jeepforum.com/forum/f12/f...grade-1054753/

1990 YJ. SOA, OME 36R 3.5" lift springs, OME 5/8 greasable shackles, OTT high steer, Custom cage, team Rush, Posi, 33 TSL swampers
giggityjeeper is offline  
post #5 of Old 07-11-2007, 04:10 PM
Burnerman
Registered User
 
Burnerman's Avatar
1996 ZJ 
 
Join Date: Oct 2006
Location: Vernon, NJ
Posts: 4,758
http://home.sprynet.com/~dale02/list.htm
It won't solve your trouble but it helped me 100%

96 ZJ.
05' Grand Cherokee Limited, 2"OME lift
Burnerman is offline  
post #6 of Old 07-11-2007, 06:07 PM
JJorda
Jeep. Jeep? Jeep! Jeep.
 
JJorda's Avatar
1989 YJ Wrangler 
 
Join Date: Jun 2004
Location: North Caldwell, NJ
Posts: 504
I had very similar symptoms, turned out to be an ignition module on the way out. I'd carry a spare in the glovebox/console just in case. Never fun when those go out on the road.

1989 Jeep Wrangler - Daily Driver and project - Red Jeep Club #216, NRA Jeep Club #5
1967 Chevelle SS396 - Main Project <--454, TH400, 4.10's, FAST
1982 Caprice Classic - Another project <-- 350/700R4, 4 wheel discs
1979 Honda Civic CVCC - Yet another project <--goal of 60 mpg
JJorda is offline  
post #7 of Old 07-15-2007, 02:21 PM Thread Starter
smsdway
Registered User
1989 YJ Wrangler 
 
Join Date: Jul 2007
Location: maine
Posts: 5
Thank you all for your help!!

I replaced the wires, plugs, pcv valve and the ignition control module (for reference, this was $71 at Carquest and $140 at Napa), needless to say, I bought it from Carquest.

Also found out that the module is loctaed under he coolant overfow bottle, NOT NEXT TO THE BATTERY WHICH IS WHERE THE CHILTON MANUAL SAYS IT IS.

Anyway, I think the backfiring and loss of RPM problem is now fixed. Took it for a 10 mile run and it ran fine. But ......

A idle it still seems to misfire. It idles at about 800 rpm and quite freqeuntly will shutter a little and the rpms will drop about 100 and then recover. I'm assuming this is a misfire, but maybe I'm not diagnosing correctly.

Any ideas on what this is or if I should even be concerned and how to fix it?
smsdway is offline  
post #8 of Old 07-15-2007, 03:17 PM
Burnerman
Registered User
 
Burnerman's Avatar
1996 ZJ 
 
Join Date: Oct 2006
Location: Vernon, NJ
Posts: 4,758
Are you still running the Carter? You need to fill out what you're running in your profile. On that link I posted above there's a fix for the carter idle problems. The idle tubes may be clogged and loading up a cylinder.

96 ZJ.
05' Grand Cherokee Limited, 2"OME lift
Burnerman is offline  
post #9 of Old 07-15-2007, 05:05 PM
giggityjeeper
Registered User
1990 YJ Wrangler 
 
Join Date: May 2007
Location: British Columbia
Posts: 4,022
Quote:
Originally Posted by smsdway
Thank you all for your help!!

I replaced the wires, plugs, pcv valve and the ignition control module (for reference, this was $71 at Carquest and $140 at Napa), needless to say, I bought it from Carquest.

Also found out that the module is loctaed under he coolant overfow bottle, NOT NEXT TO THE BATTERY WHICH IS WHERE THE CHILTON MANUAL SAYS IT IS.

Anyway, I think the backfiring and loss of RPM problem is now fixed. Took it for a 10 mile run and it ran fine. But ......

A idle it still seems to misfire. It idles at about 800 rpm and quite freqeuntly will shutter a little and the rpms will drop about 100 and then recover. I'm assuming this is a misfire, but maybe I'm not diagnosing correctly.

Any ideas on what this is or if I should even be concerned and how to fix it?
now it sounds like a vac leak or fuel problem....the ECM and wires was prolly the backfire and misfire problem, the ECM is under the collant bottle, the computer is under the pass side dash, I had to do both.....if your running the carter still consider using it for a weight for fishing or something and get somethihg else dont try and fix the carter in my opinion it is a waste of time...I tried for over a year, rebuilt it twice blah blah kept crapping out..weber......holly.....MC2100...I got hte weber about a 3 hour bolt on application and down to 4 vac lines...

only other thing maybe is the dist...with mine while under idle it wuold die and sputter but when on the highway with RPM it was fine, miss a bit but barely noticeable, if you did everything else change that as well...when I took mine off little pieces fell out of the dist, it was toaste as well....

Started with some rust repairs ended in a SOA...

http://www.jeepforum.com/forum/f12/h...-jeep-1050879/

family roll bar swap/upgrade..

http://www.jeepforum.com/forum/f12/f...grade-1054753/

1990 YJ. SOA, OME 36R 3.5" lift springs, OME 5/8 greasable shackles, OTT high steer, Custom cage, team Rush, Posi, 33 TSL swampers
giggityjeeper is offline  
post #10 of Old 07-16-2007, 07:18 AM Thread Starter
smsdway
Registered User
1989 YJ Wrangler 
 
Join Date: Jul 2007
Location: maine
Posts: 5
The Jeep is all stock, which I guess means it has the Carter Carb. I updated my profile with all te info I knew - thanks for the advice Burnerman.

I cleaned out the idle tubes in the carb as they were clogged, but still had the misfire at idle. It seems to get more pronounced as it warms up.

I don't have a vacuum gauge, but will probably pick one up soon. Can I deduce anything from pulling a line and feeling for a vacuum? For instance, I can pull the pcv valve out and block it wiht my thumb. The idle drops a bit and when I release it, there is definitely a vacuum present. Does that tell me anything?

I will try to pick up a fuel filter today just in case. But I changed the filter last year and only put about 4k on the Jeep since then. It does sit all winter in Maine though.

The fuel pump was put in about 2 years ago. I don't think that should be an issue?

If I did have a fuel pressure problem, wouldn't it be present under other conditions as well, specifically during acceleration? I do not feel any hesitation when accelerating.

What am I looking at for a new Weber Carb?

My concern is that te misfire will cause engine damage at some point or throw other systems off. If it wants to idle rough without te possibility of further damage than I can live with that.
smsdway is offline  
post #11 of Old 07-16-2007, 07:34 AM
giggityjeeper
Registered User
1990 YJ Wrangler 
 
Join Date: May 2007
Location: British Columbia
Posts: 4,022
use carb cleaner to chekc for vac leaks around the carb itself it will idle different when carb cleaner hits a vac leak...

I dont think you have a fuel problem anymore, my Weber ran me 364 Canadian shipping and all, and about 3 hours to install, and man best 365 I ever spent..

did you change your Dist yet...if not try this, mine was doing similar and would run under RPM fine but on idle would stumble,

Started with some rust repairs ended in a SOA...

http://www.jeepforum.com/forum/f12/h...-jeep-1050879/

family roll bar swap/upgrade..

http://www.jeepforum.com/forum/f12/f...grade-1054753/

1990 YJ. SOA, OME 36R 3.5" lift springs, OME 5/8 greasable shackles, OTT high steer, Custom cage, team Rush, Posi, 33 TSL swampers
giggityjeeper is offline  
post #12 of Old 07-18-2007, 05:42 AM Thread Starter
smsdway
Registered User
1989 YJ Wrangler 
 
Join Date: Jul 2007
Location: maine
Posts: 5
I just performed the "Nutter" yesterday and that fixed the misfire at idle, in addition to giving the Jeep a lot more power. I used to have to downshift on some hills from losing power and speed, but that problem appears to be gone now.

Does anyone know exactly how far out the stepper motor pins go? I got them out to where the plate (holding the pins) was about a 1/2" outside of the housing on the unit. Just want to double check.
smsdway is offline  
post #13 of Old 09-11-2015, 11:43 PM
treuss3
Registered User
 
Join Date: Sep 2015
Location: Foxboro
Posts: 3
Hopefully someone can help I have 89 wrangler yj 5 speed I have replaced throttle position sensor,ignition coil, new fuel pump sending unit and tank rotor plugs wires it stalled when warm but started right back up thought it could be fuel pressure regulator and now when I put vehicle in gear and give it gas it stalls immediately please any input is welcome thank you
treuss3 is offline  
post #14 of Old 09-12-2015, 06:40 AM
Mike Romain
Registered User
1986 CJ7 
 
Join Date: Nov 2007
Location: Off the Grid in Chester Grant
Posts: 18,090
Quote:
Originally Posted by treuss3 View Post
Hopefully someone can help I have 89 wrangler yj 5 speed I have replaced throttle position sensor,ignition coil, new fuel pump sending unit and tank rotor plugs wires it stalled when warm but started right back up thought it could be fuel pressure regulator and now when I put vehicle in gear and give it gas it stalls immediately please any input is welcome thank you
You really need your own thread. This one was for a carburetor engine, you seem to have fuel injection. When folks read to troubleshoot, they usually back up to see the original issue which isn't yours.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
Mike Romain is offline  
post #15 of Old 09-13-2015, 09:24 AM
treuss3
Registered User
 
Join Date: Sep 2015
Location: Foxboro
Posts: 3
Sorry didn't realize this forum page is kind of confusing but no need to be rude I just want a vehicle that runs
treuss3 is offline  
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Jeep Forums Replies Last Post
1990 YJ 2.5L misfire backfire under acceleration kech22 YJ Wrangler Technical Forum 5 07-07-2014 01:11 PM
Misfire 2004 Jeep Wrangler X 4.0 54urlcr TJ Wrangler Technical Forum 0 11-17-2008 08:10 PM
01 Wrangler Cylinder Misfire gotmule TJ Wrangler Technical Forum 6 11-05-2008 07:35 PM
misfire/backfire help!! tawdr77 YJ Wrangler Technical Forum 12 08-14-2008 11:31 PM
94 Wrangler 2.5 Backfire DavesMatthew YJ Wrangler Technical Forum 0 02-19-2004 09:10 AM

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome