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Possible Misfire, please help-new here

3K views 28 replies 7 participants last post by  NAJ 
#1 · (Edited)
Hello. I am the new owner (2nd) of a 1989 Daytona Shelby. 43,000 original miles according to the mopar /dealer collector I bought this from.
It appear to have a slight misfire, erratic when idling. I can kind of hear it in the exhaust, like a smooth purr then randomly dudding sound. additionally, when slwoing down in gear there is backfiring somewhat. Not like a modded ricer but enough that it is annoying. Also, when i step hard on the throttle from idle, there is a cutout or hesitation. I checked the vacuum lines and compared to the diagram, which appear to be routed properly. I also did not find any leaks. I removed the MAP sensor as found in other threads and cleaned. I also cleaned the sensor in the intake manifold. Still no luck. Vacuum is reading 15 at idle. I doubt timing is off as the car drives very well. Or, should this thing be like a rocket at all RPM's? I put a can of seafoam in the gas and going to try 91 octane when I need fuel next. I dont know if anything has ever been changed on this. Guy claims its a 2.2L and all original. I pulled a plug and it was a little gray with two black streaks on the sides of the tip.I would really this thing to run impeccable. its in the best shape I have ever seen one of these that is all original. I am just more familiar with Cummins engines than these 80's turbos. Please help or offer further troubleshooting advice.
Thanks
 
#2 ·
Welcome To TD!!!

First thing, 91 Octane is the Minimum you Have to use on a Turbo Car or you will have Detonation Issues and the Engine controller will Pull Timing or you will put a Hole in a Piston.

As far as your erratic idle and "misfire".
15" HG @ idle is minimum vacuum allowed, with a stock engine you should be at least 18" HG 2 idle.
Low engine vacuum will also cause you to run rich.
With low vacuum the engine controller assumes more air has entered and increases injector pulse width.
First thing I would do is verify all of your basics are correct.
1) Cam and Ignition Timing.
a)http://www.turbododge.com/forums/f4/f14/359212-cam-timing-belt-tension-84-95-a.html

2)Fuel Pressure
b)http://www.turbododge.com/forums/f4/f14/358339-checking-fuel-pressure-84-93-turbo.html

3)Ignition System
a)Capable of 25 KV at all 4 cylinders.(Using an adjustable spark tester)
b)Plugs are not worn

4)No Restrictions in the...
a)Exhaust System
b)Air Intake System
 
#4 ·
Welcome To TD!!!

First thing, 91 Octane is the Minimum you Have to use on a Turbo Car or you will have Detonation Issues and the Engine controller will Pull Timing or you will put a Hole in a Piston.

First thing I would do is verify all of your basics are correct.
1) Cam and Ignition Timing.
a)http://www.turbododge.com/forums/f4/f14/359212-cam-timing-belt-tension-84-95-a.html

2)Fuel Pressure
b)http://www.turbododge.com/forums/f4/f14/358339-checking-fuel-pressure-84-93-turbo.html

3)Ignition System
a)Capable of 25 KV at all 4 cylinders.(Using an adjustable spark tester)
b)Plugs are not worn

4)No Restrictions in the...
a)Exhaust System
b)Air Intake System
Ok great, thanks much for the help. If vacuum is low, how do I fix this and increase vacuum. It does smell rich, I could smell it across a parking lot.
Since the car is so old, even though the miles are low, is there anything I should just replace to be smart?
I posted where IMO you should start, checking all of your Basics starting with Cam/Ignition Timing.
Under each topic is a"Link" to a "Thread" on how to do it.

Do Not just start replacing parts because if something goes wrong you will not know if it is related to your original problem or something else.
Always Diagnose First.
 
#3 ·
Ok great, thanks much for the help. If vacuum is low, how do I fix this and increase vacuum. It does smell rich, I could smell it across a parking lot.
Since the car is so old, even though the miles are low, is there anything I should just replace to be smart?
 
#7 ·
Thanks all for the help. I'm going to check the timing this coming weekend and then go through the other steps in order. My initial thoughts were "if this car is original, who could the timing be off?" But from what I've read it can jump teeth on the belt. There are some yellow paint markings on the valve cover and cam sprocket which I noticed when I first bought the car. Could these be factory or may someone have messed with the timing and put their own paint dabs on it? I'll take some pics after work and upload.

I really like this car and want it to run right. I just hope I'm not into a money pit.
 
#8 ·
Just out of curiosity...
Is the distributor housing almost parallel to the block?
A lot of people have a hard time getting all of the marks aligned properly and the intermediate shaft which drives the distributor is usually the one that is off.
If so they would have had to turn the distributor one way or the other to get ignition timing correct so the housing will not be almost parallel to the block.
If somebody was in there that could be a tell tale sign.

 
#10 ·
Here's some
Pics. Maybe someone will know of this has been tampered with?
Ok nvm, it will not let me
Upload pics. Naj, what's your number or email and I'll fire them off. Also anyone else interested in seeing let me know.
 
#11 ·
Nice find! How long has he been sitting? If for awhile, I'd change the oil (go four quarts 10w40 and add in a quart of Marvel Mystery Oil). This stuff is awesome at dissolving deposits freeing up rings and parts in the top end. Mopar sells a combustion chamber cleaner too. If the car has been idle for ??? I'd get a can or two of the MCCC, feed the engine with it and then change the oil as above.
 
#12 ·
I'm not sure how long it has been sitting, I think a few years. Window sticker shows fresh oil, dealer claims brand new oil. He
Mentioned he thinks plugs and wires are original. But I'm not sure. Hell I even wonder what the thing is worth. I took it for a spin today and it moves pretty solid in lower gears. Seems to not accurate super fast in 4/5 gear. But I'm
Used to driving a 550hp truck also!
 
#13 ·
some updated info to my problem. I live at high altitude - 5500 ft. Would this at all affect the amount of vacuum when idling? Also, I can only find 91 in my town because of the altitude. Is it still ok to run 91 octane
 
#15 ·
some updated info to my problem. I live at high altitude - 5500 ft. Would this at all affect the amount of vacuum when idling?
It may but I cannot say for sure, I am at sea level.

I do know that at that altitude air is scarce, the Pro Stock cars in NHRA slow down over a 1/2 second when they go to Denver.
 
#16 ·
Another piece to the puzzle, when the air conditioning is on, the idle is quite different. It's cuts out more when throttling from a dead stop. Also, seems like the miss is more evident with the ac compressor on. Is this Normal?
 
#17 ·
Thanks everyone for the help so far. This weekend in going to check timing and ignition. I believe the distributor is parallel to the block. I still cannot up load pics to show.

If anyone can help with the idle issue worsening with a/c on please do!
 
#20 ·
It appear to have a slight misfire, erratic when idling. I can kind of hear it in the exhaust, like a smooth purr then randomly dudding sound. additionally, when slwoing down in gear there is backfiring somewhat. Thanks
Ramdom "duddling" at idle is normal, whenever the baro takes a sample it disrupts the purr.

Keep in mind you have a relatively heavy car with a small engine, so off idle driveaway performance will be slightly less than a Cummins. Off boost, these engines don't even make as much power an a N/A 2.2, but approx. 2500 to 5500 is the sweet spot

Even getting these cars moving off the line can require a bit of a touch to prevent stalling.

Decell backfiring isn't all that unusual especially if it has any non stock exhaust.

I've found, on an other wise good running engine, opening the hidden, your not supposed to touch, base idle screw helps with decell backfiring.

Thanks
Randy
 
#25 ·
From what I can tell and following the link above, the timing is good. It has a fresh tank of 91 with octane boost. At this point, the car is running better with a/c blasting. I hear a rattle under the passenger floor, when engaging first. Sounds like cat converter. That tin rattle sound under low vibrations.
 
#28 ·
Well it's been a while since I have been on but I still cannot hunt down the throttle cut out when I tap the gas at idle. The car will hold 1500 rpms for about 1 second after I touch the gas then drop down. I tried checking for vacuum leaks with carb cleaner and no luck finding anything. Any ideas? Your help is greatly appreciated.
 
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