I have an 85 chrysler fith avenue with the 318 in it and a 2 bbl carb. It has 86000 miles on it. When i first got it it seemed like it was firing wierd in the number 4 cylinder. i changed all of the plugs and found this one to be rather black compared to the other ones. then about a week later it started again. i was told it was probably the lean burn so i got an electronic ignition kit from summitracing. this didnt seem to help it even with the timing set correctly, new plugs,new wires, and a new coil. it didnt seem to be that much of a problem so i went ahead and put my headers on. now it is very noticible. it seems like the one cylinder isnt firing right. when i let off the throttle it backfires horribly out the one side, when i give it light throttle it hesitates and is very sluggish and sometimes stalls. please help me.

 

Have you done a compression test ?

 

Welcome to the forum.

If you have a spark tester install that between your wire and spark plug. Start up the motor and see how bright the light is. Turn off the vehicle and install the spark tester on another cylinder. Repeat the process.

If there is no difference in brightness, remove the plug from cylinder 4 and do a compression check. While you are at it, swap that plug with on on the other side, maybe 5 or 7, start up the vehicle and see if the problem goes to that cylinder. If it does, then its probably just the plug. If you have bad compression, you'll have to find out why.

Hope this helps some.

 

No i have not checked the compression yet. i was hoping that wasnt the case as i dont want to rebuild or change the motor right now. i did find a 360 with a trans and a transfer case for 200 bucks with 70000 miles on it i may just get that and put it in. any idea if i would have to change anything. i know i need to use the torque converter from the 360 but im not sure if i can use it on the stock chassis. im assuming that the tranny out of the jeep probly isnt geared that great.

 

you have a two drive car and that is a 4wd drivetrain. That motor is probably a magnum and you have a non-magnum motor. Look to see what is going on with your motor first. It may be a simple fix or a lot less costly repair than buying a motor ans swapping it in.

 

Its not a magnum motor its from a 73 jeep pickup probably the j10 im not exactly sure what the tranny is yet but i have to check it out

 

Hopefully you did not buy that motor. The V8 motors in the FSJs (Full Size Jeep) are not Mopars, they are AMC, completely different motor and will not just bolt right in.

Tranny will probably be a TH400 and the t-case will most likely be a D20 as the QT t-cases didn't come out til 74.

 

no i didnt thanks for the info

 

call around to some scrap yards, you'll want a 91 and older 318 or 360. Those will be the LA, non-magnum motors, if you need a motor that is.

 

i did a compression test and i have approximately 120lbs in all 8 cylinders witha 5 lb deviation range. so i do not believe i need the motor. Im starting to think its the valves or the cam or something

 

if it was the valves or cam then you would have a pressure deveation of a lot more than 5. Move the spark plug from that problem cylinder to another and see if the problem goes with it. Are you sure that you are getting good spark? Can you see down into the chamber?

It could be the lean burn system that is the problem.

 

Are you familiar with a " leak-down " test ? Thats cheap and dirty to do and can tell ya lots.

 

I put brand new plugs in it already after it happened. everything in the ignition system is brand new coil, wires, distributor, cap and rotor, plugs, wiring, ecu. its sparking fine it just still backfires out the one side.

 

I removed the lean burn system a while ago as i thought that it ws the culprit. didnt help the backfiring. just gave it about 5 more mpg and a bunch more power.

 

What is a leak down test?

 

A leakdown test is when you put say 110 psi in each cylinder with an air compressor. The hole you are testing must be on a compression stroke with both valves closed. ( engine is not running ). Once that cyl. is pressurized I take a short length of fuel line and I listen with it like a stethoscope. First I listen to the carb,inside the bore. If you hear alot of air you know you have intake valve probs. Than i listen to the dipstick tube and the oil filler cap, If you hear alot of air there you know you have ring probs. Than I listen to the exhaust pipe/s. If you hear alot of air there, exhaust valve problems.
I made my air fitting from an old spark plug that fits the engine you are working on, just knock off the ceramic and get a hole through the old plug so air will flow and put a airline fitting on it. Thats the broad strokes on a leak down test.

 

when i replaced the ignition i used the electronic ignition conversion from summit. it came with the ecu, and the vaccum advance distributor but every piece of the ignition system is brand new and i had it checked out by a few people to make sure it was done right.

 

Summit Racing is usually pretty good with doing their homework when it comes to making parts, at least as of late they have been.

 

summit is probably the best company to get parts from
the best part is that you get the parts quickly

 

Thats true. I ordered a set of headers for a friend yesterday and they will be here tomorrow with regular ground. Can't beat that.

 

Firing order..

 

i know they are in the right order i have a haynes manual and the ignition instructions from summit

 

pull the valve covers. check all the rockers. chances are you have a push rod threw one. it mite be a back one, on exoust side. if thats the case put new push rods, cam and lifters. i just had the same thing happen to my 88.