Off Roading Forums banner
1 - 10 of 10 Posts

·
Registered
Joined
·
829 Posts
Discussion Starter · #1 ·
Hi there,

Well, I was talking with my mechanic a bit today who has my 85 CJ7 with the 258 in it...

It's been causing me problems...gun shots coming out the exhaust at various times...

He said carbs dumping too much fuel...you need to rebuild it or something...I don't work on carbs...so I thought...great opportunity to "upgrade" from the carter to something better...chose a MC2100...

Got it on...still getting some backfiring...he had timed it a little funny to get it to run with the carter on it so i thought, no biggie, just take it back and have him time it up correctly...which he said he'd do for nothing...

Well, I went and now he says he hears what he thinks is valve noise...and there's less than 100 lbs compression in 5 and 6...

I don't think he's making stuff up trying to get my money as he's just pretty much doing diagnostic work for me and then I take it back and fix what needs fixing...

So, i guess, I don't know what to do next...a 20+ year old engine with lots of miles on it...odometer says 96K but it's not accurate due to bigger tires...

So in your best LEVE style...give me some options/ideas/routes to take...

-Valve job...does this motor have adjustable valves? cost? DIY vs Have someone else do it?
-Rebuild engine? cost? DYI vs someone else?
-Buy a rebuilt engine? cost? dyi vs someone else?
-Swap in a 4.0 with 70-80K miles and FI? cost? dyi vs someone else?
-Mechanic's a quack and doesn't know nuthin?
-Other ideas?

I had thought maybe the misfiring/loud noises were due to the ignition system giving up so I was gearing up for the TeamRush upgrade but now...?

Could the exhaust explosions cuased something to come loose or destroy something inside there?

One plus in my situation...if I feel as though I don't want to do something for whatever reason (time, expertise, etc...) I can have some kids at the high school I teach at work on it...they are always looking for projects...they do a great job...shop teacher checks everything...besides...most of the kids know way more than I do anyway...and they work for the cost of parts...

So frustrating...

Thanks
Patrick
 
G

·
If he is doing the compression test correctly, it does not lie....

Yea...you've got problems....

95K seems low to start having these problems....now, if it was 195K, then I would believe it....

It could be several things...burned intake or exhaust, broken piston ring, flat log on the cam....regardless, it sounds like the head needs to come off in order to figure out what the problem is....

As for options....unless you can get by with just a head job (pun not intended), you are looing at $1100 or more for a rebuid...and thats doing a lot of it yourself....

My first instent is to slap in a v6 or v8 FI engine....but, not a project of the faint of heart....ask me and Pnut.....

If you have to spend some money, go FI...doing the 4.0 swap is not hard....mechanically, everything will bolt right up...biggest issue is the CPS...on the 4.0 it is mounted on the bellhousing...but there is a kit to move it to the harmonic balancer.....and the wiring is actually less complicated than the computer wiring you have now....and it has been done a LOT...
 

·
Registered
Joined
·
1,748 Posts
Before we go and take on a major project, let's find out what's wrong with it first.

"It had to be timed funny."

What condition is the timing chain in? 95K is low for a 258, the thing should run forever given even marginal maintenance. Mine ran great even though it had blowby to beat the band. Timing chain on a 258 is a pretty typicl thing to go bad. If your timing chain has jumped a tooth, or maybe even if it's just sloppy, I would think this could effect your compression numbers also - valves and cylinders wouldn't be in the proper time.

Take the valve cover off and see what is going on with the valve train. Do all the valves move the same amount - is everything moving properly, any bent pushrods, any broken rocker arms, anything look not right, etc?

"Carb is dumping fuel."

Fix the carb. Get a rebuild kit. Learn to rebuild a carb. They're not that complicated, and it could just be a bad needle and seat, or a sticking float. IF you're dumping gas, that could be your backfire problem also.

Just my $0.02. These things won't cost you much $, and then you'll know more, and can make a more informed decision.

And just because you can push it in gear, doesn't mean it's hopeless. Sure, your compression might not be 100%, but maybe the rings are gummed up too. She could still run ok.

Good luck
Pete
 

·
Registered
Joined
·
10,815 Posts
"timed funny"
"lower compression in 5 and 6"
"backfiring out the back"

Uh, a shot in the dark - try it -
swap the plug wires going to 5 and 6. They may have been inadvertantly switched.

Pull those two plugs - oily? Super clean looking? Burned looking? Tell us.

I'm wondering if it's a simple remedy.


Define what he meant by "timed funny" - that could be a very significant clue right there!!!!!!!!

Timing it way off normal spec does not compensate for a rich or flooding carb, it indicates something else.

The low compression on 5 and 6, both at the rear of the engine. If it was flooding over with the new carb, it may have washed the oil off the rings on those two - the engine is tilted, liquid will drain to the rear.

Try another compression check on those two - this time add 1 tablespoon of 30 wt oil down through the plug hole, crank it over 4 or 5 times to distribute the oil, do the compression test again. Get "before" and "after" readings, post here.
 

·
Registered
Joined
·
829 Posts
Discussion Starter · #6 ·
95K is the minimum mileage...it is off due to at least bigger tires and perhaps other issues as well...maybe it is 195K...I'm not sure...

Timed funny = 10 degrees advanced vs spec of 5.

I'll see if I can get the wet and dry compression tests done...
 

·
Registered
Joined
·
10,815 Posts
10 vs 5 - no biggie -- unless he was trying to compensate for something. Being flooded, he may have liked how it started easier at 10. Did he say "why" he did it?

5 degrees more advanced would not help at all if the chain had jumped.

I was afraid he timed it waaaay advanced, like 25 or 30 - indicating another problem.

How many miles on it since swapping the carb?

Do the wet and dry compression tests before condeming anything. That should tell quite a bit. And tell us the color/condition of those 2 plugs, especially compared to the rest.
 

·
Registered
Joined
·
11,504 Posts
Regarding the carb, another common culprit it a defective float. Some are a brass or plastic tank which can develop a leak. Others are made of a black plastic foam which in time can absorb gasoline. There will be a weight spec in the rebuild kit. Don't neglect to check that.
 

·
Registered
Joined
·
829 Posts
Discussion Starter · #9 ·
He said he timed it to 10 because it idled better vs 5 degrees advanced...

There's about 5 miles on the jeep since the carb swap...

Before I swapped the carb the plugs in the back, 5 and 6...were "fouled." All oil-y and stuff...4 was a little...others didn't look bad...

I'll try to get those compression tests done...

Thanks for the help!
 

·
Registered
Joined
·
10,815 Posts
When plugs are badly fouled it often invalidates compression tests. The yukky stuff on the plugs is all inside the combustion chamber, sometimes holding a valve open a little during the test, sometimes making the rings not seal properly. (unless it's fairly clean oil, then there's other troubles.

Many engines have been rebuilt that didn't need it from that very thing.

5 miles isn't enough to clear out the yuk left over from the flooding carb. Now that you have the MC2100 it may eventually clear up.

What I'd do is dump 2 bottles of Techron Fuel Injection Cleaner in it - propably the best "safe" carbon and "yuk" cleaner around. And I'd temporarily put in one or two clicks hotter plugs in those two cylinders. Then put about 100 miles on it.
Then another compression test and put the correct plugs back in.

It takes some miles - freeway miles, not city stop and go - to get the crud out of it.

You may have already cured it by replacing the carb.

Initial Timing - leave it there at 10.

Let us know haw it fares.

BTW - make sure the PCV Valve is free, and the vent to let incoming fresh air into the engine is free as well.
 
1 - 10 of 10 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top