Calgary Jeep Association
4x4 Related Groups => Tech Talk => Topic started by: Zooguy on December 22, 2020, 08:46:42 PM
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Sorry for the rehashed topic but I am out of ideas. Any suggestions will help. Here it goes.
I have an 83 CJ7 with an AMC 360 and Holley quick fuel 600
From day one on a full rebuild it has had a misfire, making it stressful to drive. I have...
-Replaced the fuel lines and and filters
-Re-jetted it
-New plugs, wires and cap
-Tried a different distributor
-Changed the cam shaft and lifters
-New coil
-Checked and changed all vacuum lines
-Timing is checked
-Air filter is new
-checked engine ground
-fuel pressure gauge at 6lbs
-compression is fine
What have I missed.. Thanks
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Can you pin-point which cylinder is misfiring? Or is it a random misfire on all cylinders?
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I think it is just random.
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Check all the electrical wiring between the coil and battery. Could be an intermittent break in connection anywhere in the circuit, ignition switch, etc.
I had a GM many years ago that would have a random sputter and it turned out to be a bad wire in the distributor below the rotor cap, it was hell to track down.
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Perfect, I will give it a shot.
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Check for any vacuum leaks. Also, I can’t recall but what ignition system does this use? Is there an ignition box that can be going bad? I know Ford and chrysler in these years had issues.
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I will double check the vacuum but I think I have checked it all. I don’t think I have an ignition box. I have a MSD 8523 distributor with electronic points and a blaster 2 coil. The guy who wired it did a poor job, a lot of loose wires and bad grounds. Aside from the misfiring problem, I have had signal, dash light, stereo issues. All down to poor wiring. It is not my strong point to diagnose either. Thanks for the input, I will take another look.
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Maybe pull valve covers off and make sure each valve is opening all the way. Wiped out cam lobe or collapsed lifter.
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Is it consistent or completely random?
Consistent
Maybe need to check the timing chain. How much advance are you running? How much compression? Premium fuel vs regular make any difference?
Random
-any trend to it? After idling? Getting on throttle hard? Ambient temp?
Does it just miss or stall right out?
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Sorry for the late response, I haven’t had time in the Jeep the last little while. It is unfortunately relatively consistent. The timing chain is fine, advance is about -8 and the compression is fine across the board. I think around 120-130 ish. With the older style engine I have been told 87 octane is all I need I and am sure I have tried 91 with no differences. The trends of the miss fire are a bit weird. Starting is fine but the last couple test drives it started to miss fire at the same point in the drive about 10 minutes in. Totally fine up to that point. If I let off the throttle it will completely stall but if I give it full throttle it will get fumed off but keep running, barely. I can usually get it back home. If it does stall, I wait one minute then it starts fine but will get tempermental right off the start. Ambient temperature doesn’t seem to matter. I am going to try to solder some of the wires off the distributor this weekend to see if that helps. It was running pretty hot also if I tried to drive it for long. Valves are good. We have tried to tune the carb but last time I think we made it worst with the high speed idle. Jets are good though. I am hoping the soldering and a carb adjustment this weekend might help but it am losing faith in it being reliable for a drive. It’s almost completely rebuilt.
Thanks for reading this novel.
How do I post pictures? It is pretty to look at.
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I’ve been searching the web and maybe a loose Tach wire is causing it...maybe. I’ll check tomorrow.
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I think you’re on the right track with it being and electrical issue. Keep plugging away and check every electrical connection you can find. Maybe start shaking all the wiring harnesses while it’s running to see if you can replicate it.
Just spit-balling here but maybe spray water over all the engine electrical connections with the engine running to see if you can find a weak link?
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Checked the wiring today and it seemed to help. I solder a few that looked weak. It was one of my better test drives. I thought I would try to adjust the carb while i was at it and noticed something a bit strange. I can tighten the idle screws on either side of the carb all the way and it doesn’t stall. Why is that? High speed feels better and I turned the secondary screw out a bit. The only time the jeep seemed to have trouble is when I gave it too much gas too quickly. It then stuttered and I had to back off. It will get to speed but I have to get it there slowly. But a step in the right direction.
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Everything here sounds to me like a carb issue, not spark. Especially cranking down the mixture screws not having much effect. Do you have a vacuum guage? Thats the best way of tuning a carb short of putting an O2 sensor in the exhaust. Without one your best best is to tune mixture screw for highest idle, reset idle screw, recheck timing, then reset mixture screw again and recheck everything still it stays the same. Also make sure the choke is fully opening.
Pull the plugs, sooty black-running rich
Check for vacuum leaks, brake booster diaphram and distributor vacuum line are often overlooked culprits.
Fuel boiling in the lines or carb bowls can cause theses symptoms as well. Does it have a fuel return? Lines routed too close to exhaust.
I don't know anything about the Holley quickshot, but I played with lots of older Holleys. Pain in the arse, everyone of them. Way too much adjustability and super finicky. Floats bounced on every big bump offroad causing a floodout, Steep climbs caused bowls to overflow, floodout. Had to rest mixture and choke settings at every season change. Tried all sorts of tricks, spring loaded needle and seats, overflow tubes, etc. Ended up going to an Edelbrock Truck Avenger carb and having WAY less issues.
What did you put in for a cam? Anything radical? Still idles nice or lopes?
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Thanks for the suggestions. I feel like it is now the carb also. I don’t have a vacuum gauge but maybe I should get one. The plugs when I last pulled them looked good. I should try again though. I am pretty sure I don’t have vacuum leaks. And I have replaced the fuel lines with braided line and as far away from the exhaust as I can. I also put in a carb spacer incase it was transferring heat.
For my cam I actually put in a tamer one. It had one with a 292 open duration so I replaced it with a 252. It will mostly be a pavement queen.
Any suggestions on good mechanics to adjust the carb? I am ok with throwing a bit of money at it if I can’t figure it out. Again thanks for the input.
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With my holly truck avenger on an older 350, I get an annoying idle miss fire with the idle screws 1/16" of a turn either direction from being perfectly bang on. I highly recommend a wideband O2 sensor with an A/F gauge, tuning a carb without one is a lost art, even going off of feel/RPM I was still way out until I used the gauge. going from a 10 to 13.5 mixture will give you almost 1/3 better fuel economy. The gauge will pay for itself x5 easily in fuel consumption and unnecessary stress after a few big trips. (Going from 5-8 mpg to almost 12).
It will also help diagnose future carb / engine problems including vacuum leaks, stuck chokes, clogged fuel filters, flooding, stumbles during power transitions (coasting to power), stumbles at 10-100% throttle, fine tuning the accelerator pumps and secondary's, backfires etc.
https://www.amazon.ca/AEM-30-4110-UEGO-Ratio-Gauge/dp/B00N3VGPYS/ref=asc_df_B00N3VGPYS/?tag=googleshopc0c-20&linkCode=df0&hvadid=292977936168&hvpos=&hvnetw=g&hvrand=6573167427041104759&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9001313&hvtargid=pla-377903111462&psc=1
You need to be completely at 185F engine temp or hotter to accurately tune anything. Is this an electric choke or mechanical? you didn't mention this at all in your previous posts. If electrical, and it dies after 10 min it may not be opening causing a rich situation - possible electrical issue but incredibly easy to fix properly or just with a zip tie to troubleshoot. I doubt it is anything else electrical, as they really only need two hot wires to work - 12 volt ignition to the distributor and starter crank power, the rest are just accessories. It could also be the speed the choke is opening, possibly to soon? Adjusted by turning the black disk on the side clockwise or counterclockwise.
Timing is at 8....that's 8 degrees with no vac advance or total? Idle total advance, vac + mech should be in the 25-40* range, usually the more the better, I dont know offhand what a 360 and your cylinder heads like but in that range.
even if there is a huge vacuum leak, the miss should go away at WOT / zero vacuum.
Keep in mind;
Idle screws are idle af ratio
mid range power is primaries and the idle mixture together. Not just primaries.
WOT is idle mixture + primaries + secondary's. All three combined, plus the accelerator pumps if you really got on it.
A properly tuned 360 should be able to really test your AMC 20 2 piece axle strength on pavement if you still have that rear-end.
My services can be available with a complete holly jet kit, timing lights, vac gauges etc for a small fee ;) plus I cant even remember what a CJ7 is supposed to look like anymore. I have spent enough time and money tuning a carb I could have changed over to fuel injection now but that's another story.
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I didn’t think of an O2 sensor. It sounds like it would help to dial it in only if I know what’s wrong. I’ve been told that maybe I have to adjust the butterfly valves on the bottom of the carb if my idle screws are going all the way in without stalling. Also I’m not sure if my choke is set properly. A gauge wouldn’t tell me what’s wrong, only that something is wrong. Those are just my initial thoughts so I will research a bit and get a better understanding.
I have an electrical choke on the side of the carb.
The timing was set at Idle and might be between 6-8. We didn’t check it at higher rpms.
It does have the AMC 20 in it. I checked the gears and it looks like it has 273 open, with T5 and 35’s. I don’t mind the gears since it will mainly be on the road. But I might change to 33s once the 35s wear down. They are brand new so that will be a while.
Thanks again for the suggestions, I will research a bit and DM you for some help if I can’t get it right soon.
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Is the carb new(fairly new)? Not something bought 2nd hand? If so the throttle plates should be set correctly and I would avoid playing with them as that would add a whole new set of parameters to the mix.
A vacuum guage lets you see whats going on as you drive, not as accurate as a O2 sensor but still handy and easier, also handy to watch while adjusting at idle and a fairly cheap.
Is your vaccum advance hooked to ported or manifold? Did you disconnect and plug it when setting the timing? If not then you might not have enough base advance timing. If you are not sure the difference on ported vs manifold then do a google search, easy to find.
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It is a new carb, but since the cam that I replaced had a 292 open duration I suspect he messed with the carb a lot in order for it to run. With the internet research I’ve done, one possibility is the throttle plates and it seems to sound like my symptoms. I did try to use a vacuum gauge to tune it which seemed to help. It went up two numbers to 15. But the idle screws can still be bottomed out. I only tried the manifold vacuum when tuning it at Idle. Thanks for the suggestions
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I took the carb off and adjusted the throttle plates so the the “gas port”? was squared off. The idle screws can still almost bottom out but it runs much better. It still stumbled a little at full throttle but much better than before. The air fuel gauge sounds appealing to tune it a bit better. So a step in the right direction. Thanks.
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And two steps back. I took the Jeep out for a drive today and it started to act up after about 30 min. I am starting to think one of the issues is vapour lock. After I got home I saw a couple bubbles in the float bowl. Maybe a heat shield would help. I am also thinking of running the fuel lines in the frame. Thoughts?
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How close to the exhaust and manifold coolant passages are your fuel lines? you should be able to touch the fuel lines bar handed everywhere they run.
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And two steps back. I took the Jeep out for a drive today and it started to act up after about 30 min. I am starting to think one of the issues is vapour lock. After I got home I saw a couple bubbles in the float bowl. Maybe a heat shield would help. I am also thinking of running the fuel lines in the frame. Thoughts?
Centuries ago, back in my carb days, we used aluminum heat shields and spacers between the carb and intake manifold all the time. They work well and are super effective. We would also wrap fuel line that were near "hot areas" with header wrap however now there are heat shield wraps that attach with velcro that are fantastic, Mopac has a good selection.
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How close to the exhaust and manifold coolant passages are your fuel lines? you should be able to touch the fuel lines bar handed everywhere they run.
The fuel lines were in some places about 6 inches away. My Jeep has run hot from the start. I ended up running the lines through the frame so it will hopefully be a non issue.
Thanks for the reply.
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Centuries ago, back in my carb days, we used aluminum heat shields and spacers between the carb and intake manifold all the time. They work well and are super effective. We would also wrap fuel line that were near "hot areas" with header wrap however now there are heat shield wraps that attach with velcro that are fantastic, Mopac has a good selection.
I ended up putting on a heat shield and some of the heat material around the gas lines. I ran the fuel lines through the frame also. I haven’t had time to get it out but when I started it the idle was about 1500 and hard to get down and stay steady. I will try to make some time this weekend.
Thanks for the suggestions, hopefully this will help.