I’ve a 1973 CJ5, 232ci with 390 Holley, headers, mild cam, electronic distributor, thats run excellent for the 35 years Ive owned it. It hasnt been driven much in the last 2 years but started once a month. I did drive it in June, then in July when I started it, it would stall immediately. (Nothing different in between) I remembered I hadnt change the gas that sat in the tank all that time! I did the usual things to resolve, Its a new carb but took it apart and installed a new kit, took out the tank, filled with new gas, new lines and filter. Tank was spotless inside. Fuel pump 7-9psi and can fill a quart jar in 30 sec. New plugs, cap and rotor. Checked the coil, wires, spark, timing (5’btdc), checked for vacuum leaks and put in a new exhaust/intake gasket as I was getting a steady 6-8hg at the carb base (to low?), PCV OK, compression between 112-118psi on all six cylinders, (a little low but its been bored 30 over.)
The kicker is that I can get it to run if I retard the timing to ~5-10 aftc but it wont take any trottle. Opening it will kill the engine and moving the distributor towards advanced, itll start to surge and finally quit with a significant blowback.
Its past its AZ inspection and Ill need to get it fixed before it gets hauled away (maybe not a bad idea).
Im not a car mechanic, (I build cleanrooms for Intel) but its the first vehicle I ever owned and I can work on it with my eyes closed, maybe now I need new glasses.
My choices are: 1) Youse guys have the answer, 2)Tow it to a garage (nobody but me’s ever worked on it!!), 3)Sell the GMC I bought last year cause i think the Jeep is jealous 4)Ask my wife what to do, sees an astrologist and reads Tarot cards.
Check to make sure the timing chain hasn’t jumped time.
Tester
The compression numbers are way too low and the manifold vacuum is also way too low, but that could be the result of low compression.
The compression readings in an engine will vary a bit based on altitude and barometric pressure, but the rule of thumb is that the compression reading in a good engine should be equivalent to 15 to 18 X the compression ratio.
(10 to 1 compression - 150-180 PSI.)
Manifold vacuum will vary (again, altitude and baro pressure) but a half decent engine should be pulling about 16 to 20" of vacuum.
If the vehicle were mine I’d run a wet compression test on it. This means remove the plugs, prop open the throttle, and give each cylinder a small squirt of oil before you retest it. If the readings take a significant jump upwards (say 112 up to 140 PSI) then there is a piston ring problem. The readings stay low then you should suspect a cylinder head valve problem. Hope that helps.
Thanks, I did the test and the compression went to 138/140/135/142/135/132 (1-6 cyl). Sounds like a ring problem probably from sitting to long?? Thats why it will only run with a retarded timing as there isnt enough energy to overcome compression BTDC??
Bummer. Any easy way to fix it? It only has 30k miles since rebuilt 18 years ago
Those numbers are definitely low and JMHO here, but my feeling is that the problem could be caused by one of two things; or a combination of both.
An engine will run on the higher numbers but will be somewhat lacking in power. It would surprise me if an engine would run at all on the lower numbers; or even get out of its own way power-wise.
One is that short hop driving and occassional use could have sludged up the piston rings in the piston ring lands causing them to stick. The piston rings should all have free movement while the engine is running.
Two is that there was a problem with the quality of the rebuild and/or breakin period; improper honing or out of round cylinder bores, rings installed upside down, etc., etc.
I would set the ignition timing where it’s supposed to be. Running too retarded can very well cause low manifold vacuum readings and loss of power to boot.
About all I can suggest since there is an apparent ring problem, and assuming it could be sludge related, is try an additive in the engine oil and see what happens over a couple of weeks time. SeaFoam is inexpensive, has a good cutting action to it, and is a very good product.
Hope that helps anyay.
I put the Seafoam in the oil and did a little down the carb as it suggests. No immediate improvement but it may need to sit. I cant drive it now only run with the timing retarded but at least allows the oil to circulate. When running and as I try advancing the timing, the vacuum does increase but surges with the engine speed until it quits.
BTW I also check the TDC position for #1 cylinder, all looks well
Ill start it daily for a few days to see if the rings loosen up
Thanks youve been a great help and Ill keep you posted
Gary
I’m going to back up here a couple of steps. While pondering your problem I forgot about the part where you mention having a mild cam in it.
The camshaft profile can affect engine compression and manifold vacuum but generally it has to be more than a “mild” cam, although the term “mild” can be used to mean various degrees.
The camshaft timing can also affect this so this goes back to Tester’s post. One would not think a cam chain on a rebuilt engine would jump time but how sure are you the camshaft was properly timed, or degreed?
Why would anyone put headers and a cam in a 232 AMC six?? A Rambler motor…
Your PROBLEM sounds like the exhaust is obstructed or the timing chain has jumped over the gear teeth.
How many miles on this engine?? The FIRST TIME you checked the timing, was it set properly?? If it was, then the timing chain is Ok…If it jumps time, the ignition timing will also change, usually retarding itself 20 or 30 degrees…
You can check that for sure by removing the #1 plug and observing the piston and timing mark to make sure the piston and timing mark agree where TDC is…
If that checks out, open the exhaust at the collector and see if that improves things.
There is always the chance your aftermarket ignition system has decided to go into the twilight zone. Does it produce a nice, fat, clean spark at the coil wire?
Money was the main reason for the headers, carb etc. Couldnt afford a swap at the time. Being young and impetuous didnt help either. Think I put them on in 1976. The engine has been running fine for the last 30-35k miles (over 18 years) since the rebuild. Ran great before that. The #1 TDC checks out, havent checked to see if a potato or something stuck in the exhaust (ill look tonite). The timing chain and gears are steel, hard to understand how it could jump but its on my list to check if i end up tearing it down. The cam is a Crane (as i remember) one step up from stock and since all the emmisions stuff fell off when the warranty ran out, Its been able to pass AZ’s testing every year. The DUI distributor seems fine, good spark, coil resistance meets spec. The thing that bugs me is the, one day it worked, the next time (a month later) it didnt. Sabatage could explain that, old gas maybe, timing chain. My wife says that Mercury went retrograde and that messes up transportation things. Thanks for you help
It’s not a cam profile issue if it was running fine before and it’s hard for me to see a chain jumping. If it was that loose you should have heard it clattering.
About all I can recommend is make sure the chain and timing marks all line up, set the timing properly, and since the vehicle should be converterless you should not have a problem with a plugged cat.
If marks line up then it appears to me you have a piston ring problem due to the significant jump upwards in compression readings.
This could be verified with a leak-down test. That will require a few specialty tools.
As long as those readings are that low and the timing is way late then it will continue to be somewhat of a dog. Won’t take any throttle could be the late timing and/or a clogged accelerator pump circuit in the carburetor.
(That extremely low manifold vacuum is also a real issue as I’m having a hard timing seeing how timing alone would cause it to drop that much. Timing, low compression, etc. could possibly do it though.)
Well I check the tail pipe, no potato and plenty of flow. I put a bit of the seafoam in the cylinder to sit and Ill try it again tonite. The plugs are obviously black running retarded as it is. Im down to sticking it in tha garage and checking the timing chain or pulling the head to see if theres a gasket problem.
i first thougth the Tappet bros would be answering these but youve all been a great help and i do appreciate it
Another possibility here. Have you removed the air cleaner top and verified that the air cleaner is not full of stuff stashed in there by rats?
Slim odds I know but a VW was towed into the shop one time that would barely even run and the housing was completely full of dog food. Rats had gnawed their way in and had turned the air cleaner into their own personal bank vault. The owner stated that he had noticed the car running worse and worse over time.
Personally I would not remove the head as I don’t think a gasket is at fault. The soot on the plugs could be caused by retarded timing and the low compression can do the same thing.
Tom and Ray do not post here and not meaning to sound too crass here, but T and R are not exactly top of the line technicians to be blunt; although the perception may be they’re wrench gods.
Im sure they have a good support team behind the mic but they execute well. ive been doing these tests without the air filter. I think Id like to take a pic so you can see the engine. It seams that, from what Ive read about the compression cycle, when I advance the distributor and the RPMs surge up and down until it quits, that the energy is reacting against something other then just 120psi compression. It may be low but seams I remember checking it long ago and was similar… maybe some valves arent opening correctly?
SUCCESS!
Well today Mercury went direct which removed all the transportation snafus that planet causes. My wife can tell me her I told ya so’s. I recalled today the only thing I wasnt able to test was the ignition module inside the distributor as I dont have the equipment. I called DUI and the tech told me what the problem was before I was able to finish explaining it. NAPA tested it and sure enough it was totally bad and replaced it for $24 ( I got the cheap one). 20 minutes later it was running like it always has.
The good thing outta this whole episode was I found a great site to ask car questions and get great advice from smart people. The another is I theres not much left to check or replace so it should run fine for a while. The last is I dont have to pull the Vardo outta the garage to tear the Jeep down (www.armadillotile.com)
Thanks all for the help and especially ok4450 for hanging with it
Glad it’s got you fixed up but those compression readings are still pretty shaky.
Another possibility (although faint) could be that the engine was running so badly that excess gasoline was keeping the cylinder walls washed down.
Don’t know if retesting the compression in a couple of days would shed some more light on this or not.
Interesting about being an artist and classical guitar builder. I used to do a lot of artwork and in my younger days considered it as a profession (won a couple of local art contests) but the monetary reality stopped that and anymore when I attempt it brain freeze sets in and I just sit and stare blankly. “Visual Writer’s Block” I guess? I’m also a frustrated bassist; something else that never went anywhere although it does serve as a stringed tranquilizer for me currently. 
The cam, altitude and age might explain the slightly weak compression. Some guys don’t know about holding the throttle wide open…
As long as the compression is nice and even between cylinders, I would not worry about it too much…
Another possible cause of “low compression” is a leaking Schrader valve on the compression tester.
That’s why I’ve always run a compression test twice (and even 3 times) when a potential engine problem surfaces. The test is also never performed with the same gauge. It’s done with several others just to weed out a potential compression tester problem.
Something else has occurred to me. The OP says it has manifold vacuum of 6-8" at the carburetor BASE.
Any chance this vacuum nipple provides a ported vacuum reading from above the throttle plates? I know with a properly adjusted throttle plate it should not be this high but if the throttle plate has been opened a bit too much due to the adjustment screw then it’s possible this reading could occur and is not a true indicator of manifold vacuum.
The vac is now 16hg and steady. Ill check the compression once again as suggested, Id like to see how the seafoam treatment helped. The gauge i used was new and came from my favorite chinese tool supply store (more jobs shipped overseas), but it was consistant and didnt seem to leak.
The artwork is focused on building the vardo. Im rebuilding a old guitar with a new top and I agree about the tranquilizer effect. Good way to escape and not wake up with a hangover
Ditto on the stringed tranqulizer. I spend some time almost every evening with a high end Washburn, found after years of searching for the perfect instrument for me. I found it. Arthritis has eliminated most of my bar chords and made me change the key on a lot of music, and change my style, but it’s still a pleasure…even if the pain and stiffness now limits the music.
How DOES Les Paul do it?
Les Paul is a pretty amazing guy is he not? I think he’s 93 now and still tearing it up on the guitar named after him.
Washburns are pretty nice rigs also. I’m a bassist simply because I’ve always found myself following the bass line; just like a moth to a porch light.
However, I’m been trying to take up the 6 string the last few months due to a freebie.
One day a large package sent by my sister (lives in TX) arrived by UPS. I had no idea what it could be and lo and behold, Xmas came early.
My sister is into acoustics and her hubby decided to give the guitar a whirl. A few times and he gave it up so he decided to send his guitar up to me.
A brand new professionally setup Telecaster with accessories all gratis. While not really a Tele freak, for free I can learn to love it.
Now if I can talk my son out of his Les Paul…