1987 4 cyl MJ Rough running condition

[jeepogeek]

Good news, for me anyway.  The MJ runs again, thanks to you guys.  But, you know, buying a vehicle on the side of the road...you solve one problem and discover another.  The engine runs, but not good at all.  it misses terribly  So I pulled the plugs and all of them are very sooty, or have carbon build up.  is this a typical symptom for these engines with 230k on the clock?    

[eaglescout526]

Could be. But there are other things that can cause the engine to run rough. Start with grounds and a tune up and we can move on from there. 

[jdog]

Could be, do cruisers tips, check the c101 connector for corrosion. Do a full tune up wires, plugs, cap and rotor

[jeepogeek]

Interesting.  Thanks!

 

So what I'm faced with now is pretty rough running motor and carbon coated plugs.  Exhaust seems to smell like rich mixture, but I don't know what to do about it.  Maybe a vacuum leak?  Any ideas?

[eaglescout526]

Pretty much its a start testing every sensor for proper operation and checking vacuum hoses.

[jdog]

Look into getting a REM it'll help in telling what sensors are doing what

[jeepogeek]

Thanks guys for the suggestions.  I guess I need a repair manual for the truck.  Can anyone tell me what manual they would recommend for this rich running situation that I have?

 

 

[jdog]

best manual is jeep manual, theres a downloadable link on here, i believe its in @Pete M signature

[eaglescout526]

AMC|Jeep TBI Book is a must for the mighty lil 2.5L.

[jeepogeek]

Thanks guys for the suggestions.  I guess I need a repair manual for the truck.  Can anyone tell me what manual they would recommend for this rich running situation that I have?

 

I found my Jeep manual M.R.244 that says it's revised July 1985.  I also found my Haynes 1984 thru 2000 repair manual.  I ordered from Ebay the TBI book and a similar Jeep 4cyl engine service manual.  I presume these manuals will help me with the 1987 MJ that I now own.

I'm also considering the REM as suggested here by jdog.  It makes sense to use a tool like this instead of chasing my tail trying to check these components without the electrical experience of some of the folks here.  Are there any other suggestions that could help me with the rough running sooty plug condition that my truch has.  Oh, by the way, I lost the connection to the fuel pump again.  Then it came back, and then I lost it again.  I guess I have a dead short somewhere.  And, the spark plugs in the truck are NGKIFR5G 11.  Ideas?

[eaglescout526]

TPS adjustment sounds to be in order. The TBI book will tell you how to do that and its specs on where you want it to be in terms of voltage output to the ECU. NGK plugs are fine. 

[jeepogeek]

Thanks guys for the suggestions.  I guess I need a repair manual for the truck.  Can anyone tell me what manual they would recommend for this rich running situation that I have?

 

Did I say something?  How do we know that theTPS is in good shape?

[eaglescout526]

Factory Service Manual is the way to go for all repairs. The TBI book I mentioned that you got will greatly help diag the rich situation as will an REM. The TPS can be out of wack and causing it to run rich. Check the vacuum lines to the MAP sensor on the firewall. If any of them are cracked or damaged, the MAP will feel the loss of vacuum power from the intake and dump fuel into the engine thinking it is starving for fuel. 

 

The TBI book will help you out greatly with the sensors and what their specs should be.

[jeepogeek]

 

Thanks guys for the suggestions.  I guess I need a repair manual for the truck.  Can anyone tell me what manual they would recommend for this rich running situation that I have?

 

Thank you very much for the explanation.   I won't be getting the TBI book for who knows how long since the mail seems to be screwed up sometimes lately.  But I'll look into it.  I just put new Champion plugs in to no avail but I didn't think they would cure the rough running.  I did notice the one's I removed were wet with fuel on one side of the base so I guess that confirms that the engine is receiving too much fuel.  Let me ask you, are these motors notorious for acting up this way?  Something I noticed too was this.  when I put the key to power on, the tach goes to 1000 rpm.  Then when I go to start the engine, the tach mic's out all the way to the right and the TEMP gauge wiggles crazy like all wacko.  Does that tell you anything?  I have no lamps on the dash lighting either.  

[derf]

I have a Haynes manual that helps with 80-90% of what I need.

 

Nothing really beats a factory service manual though.  There are plenty of places to download and/or buy print manuals out there.

[jeepogeek]

Thanks guys for the suggestions.  I guess I need a repair manual for the truck.  Can anyone tell me what manual they would recommend for this rich running situation that I have?

 

Thanks derf.  Yeah, I do have the factory manual too.  

[Ωhm]

Guy on here had a 2.5L running RICH. Had a bad fuel pressure regulator. His problem was spitting fuel out the hole shown in the photo when engine was running. Something to check for.

 

[eaglescout526]

When a sensor goes out of spec, the ECU will make the engine act up. Otherwise no these engines run really solid. 

[54bobby]

2 hours ago, Ωhm said:

Guy on here had a 2.5L running RICH. Had a bad fuel pressure regulator. His problem was spitting fuel out the hole shown in the photo when engine was running. Something to check for.

that guy was me and after pulling the tb and rebuilding the fpr along with a good cleaning my flooding out condition and the terrible ruff idle and stumbiling  was cured. you will need to both clean and readjust both iac valve and the tps, in that order i do believe.

 

[Ωhm]

10 minutes ago, 54bobby said:

that guy was me and after pulling the tb and rebuilding the fpr along with a good cleaning my flooding out condition and the terrible ruff idle and stumbiling  was cured. you will need to both clean and readjust both iac valve and the tps, in that order i do believe.

 

@54bobby. Thanks for the follow up.

[jeepogeek]

Thanks guys for the suggestions.  I guess I need a repair manual for the truck.  Can anyone tell me what manual they would recommend for this rich running situation that I have?

 

Wow!  Thank you very much for all this information.  As a mere fledgling mechanic with very little later model car experience it will be difficult to wade through this much material.  But I want to try to do it anyway.  The last bit of rebuilding I did was to rebuild a Rochester Quadrajet carburetor. which actually came out great.  But these engines with computers are intimidating to me.  I hope the TBI book goes into the fuel pressure regulator rebuild  and I don't have to have a bunch of specialized tools and knowledge.  I really appreciate all the advice.  I definitely need it.

[eaglescout526]

Actually the Fuel pressure regulator is the same concept as to what you would find on a carb regulator. No special tools are needed to rebuild the TBI's but special care is to be heavily noted with the injector retainer screws. 

 

So the regulator consists of the diaphragm, a spring, the housing and an adjustment bolt that is either plugged off or exposed. But hopefully you won't have to do a rebuild of the TBI but its still easy to rebuild.

 

 All you need for our Renix system is a good multimeter, some torx bits for the TPS, some books and the passion to fix the problem at hand. 

 

We are all here to help you out.

[jeepogeek]

Thanks for the vote of confidence.  I'll do my best to get this thing on the road again.  In regards to the parts for the fuel pressure regulator, the sensors, etc., what is the best source for that stuff? 

 

 

[eaglescout526]

OEM if possible. Otherwise its a crap shoot at your local parts store. Some brands like Napa are usually pretty good but autozone is usually avoided.  Depending on what you need I can look up parts and tell you whats available and whats not.

[jeepogeek]

Thank you .  At the moment I'm interested in the fuel pressure regulator since indications seem to be pointing to fuel delivery as the problem.  So where would you suggest I get those parts?