Could anyone help me figuring this out?
I have a 1987 slant six Ram Van with auto tranny.
The engine howewer most likely isn't original and it probably is a mix of older block, newer head or something like that. (Wasn't able to ID it yet).
I'm getting really bad gas mileage (around 8 mpg), so i tried to play around a little with the engine.
I can feel that i do have a misfire, when idling in gear, but it didn't feel all that bad.
The wires, distributor cap and plugs(champion) are all new, so i don't suspect any of these would be bad.
When idling in park, i have pulled #1 sparkplug wire off the plug and i could immediatelly feel that the engine is missing that cylinder's work.
Ok
So i put it back on and move to #2....same thing
#3 ...same thing
So
Then i get to pull #4 and it has made only VERY LITTLE difference, almost as if nothing happened.
#5 and six, also very little happened........
So i took a wire off #3 and switched it with #4 and #3 was still performing good, while #4 was doing nothing much.
Then i did the same with the plugs...still the same.
So therefore i determined, that the plugs and the wires are good, so something else is causing my problem.
I also switched the firing order between #$ and #5, out of curiosity to see what will happen.
The engine just kept running, like before, like nothing has happened, no backfires of any kind.
The guy who worked on my van when i first got it few months ago did the compression test and i remember him saying that it was good and consistent across the board.
(Can't remember the actual numbers, neither can he).
So what else could be left?
If the timing was off, wouldn't all the cylinders be acting-up?
This problem seems to be isolated to #4 #5 and #6cylinders.
So now i know, why my mileage sucks, since most of the work is being done by 3 cylinders out of 6, but you could never tell just by driving down the road, because it drives pretty good.
I"m totally baffled by this, and i would apreciatte if anyone could put me on the right track.
Thank you in advance for any reply's.

hook up a manifold vacuum gage. It will tell you if you have manifold leaks,burned valve, valve adjusted wrong(solid lifter motor),and a bunch of other stuff. Im just installed an under dash vacuum gage and it's great to see how good the engine is running. Good luck.
D150

I recommend you adjust the valves. This is a common problem with old slants, and will make them miss or lose power on some or all cylinders.

Lou

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Home of Slant6-powered fun machines since 1988

I just got back from the shop, we did the compression test again and it is all in the 120 range, my question is, if the compression is good, would it still need the valve adjustement?
My mechanic seems to belive, that there is something funny going on with the distributor, because it wobbles a little, even when bolted down really tight.(It dosen't actually move around or move by itself, but when he grabbed it he could feel it is somewhat loose)
As i said before i have a pretty good mix of different parts going on, so far all i know is that the engine head seems to be 1987, since it fits the 87 spark plugs, but i don't think the bottom is original.
The distributor has a single pickup and a vacuum advance, but when i went to the part store to see if i can get a new one, they only show a double pickup was available under 1987.
Question:
Do the distributors from different years have a slightly different fit, yet could be still mismatched?
I will also bring-up the valve issue , other than that, the mechanic could not belive, that even after i disconnected 3 cylinders, the engine just kept running like nothing has happened....

A leak-down test may tell you more.
What do the individual plugs look like? Are they all the same color? Do they all have the same kind of deposits? Having the compression the same across the board is good, but 120psi is not that good(not bad, just not that good). If it is a hydraulic lifter motor, I still think you can adjust them too tight. I guess I'd pop off the v. cover, and watch it idle/run. Compare 1,2,3 with 4,5,6. Maybe when running, the lifters pump-up and hold the valves open slightly. If everything looks OK, then I'd follow the shop manual's procedure for adjusting the lash. Go slowly when you tighten the valves, because it has to bleed out excess oil from the lifter, and it will temporarily make the engine run roughly. I don't know what spec they spell out, but I'd only tighten about one turn past when they stop clicking.
The dual pick-up is for the lean-burn type computer controlled ignition. Somebody has pitched that, and you're probably better off for it, as long as the rest of the conversion is done properly.

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'66 Cuda 225/4spd
'66 Dart GT convertible 225/auto
'64 Dart GT 340/4spd

Just a couple more thoughts:
I don't think it has anything to do with the distibutor, because every other firing is weak. I can't think of anything electro-mechanical to cause such a consistent (mis)firing pattern. If it's not solved by readjusting the valves, I am tending to believe it is an int manifold/ carb problem. Is this a 'super-six' 2bbl setup? I am not real familiar with those. Is this a dual-plane intake manifold? If it is a dual-plane manifold, then you have a crack in the part of the manifold feeding those (4,5,6) three cylinders. It is leaning out those cylinders and you're getting lean mis-fire. Another possibility is one(feeding those cylinders) of the two bbls mixture is seriously maladjusted. In any case the plug reading could point you in the right direction. If the problem cylinders' plugs look white while the rest are brown/tan, they're lean. If they look kinda blackish, they aren't firing, and it's an ignition problem.

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'66 Cuda 225/4spd
'66 Dart GT convertible 225/auto
'64 Dart GT 340/4spd

Thanx for the reply's, as soon as you mentioned a conversion, it is all starting to make sense now.
It does look like someone was playing around with the wires, un-fortunatelly it looks like a monkey job, since there is mysterious wires leading all over, and than there is wires that are just hanging un-plugged from god knows what.
The vehicle's wiring job scares the heck out of me, since i don't know anything about wiring and i guess that all that could be wrong is one bad wire somewhere.
I do know of one guy, who might be able to figure it out so i will ask him to take a look.
In the meantime, i will replace the distributor with exact same one, as it is relatively in-expensive piece of mind and it could be part of the answer.
I will post the results from the distributor change and possible valve adjustement as soon as it is done.
Thanx again

My first post-here goes! Wolfears...have you checked the resistance of your coil/plug wires? I have personally seen a LOT of "new" plug wires with excessive resistance (ohms on a ohm-meter or DVOM) in them. Most mechanics don't seem to check this out when doing a tune-up, whether re-using or replacing plug wire sets. I am very picky about this...high resistance (over 2000 ohms)in any plug wire hurts the performance of your ignition. And the resistance in your coil wire must be added to that of any one plug wire to figure that cylinder's ignition wire resistance...I've had good results with the Borg-Warner Nascar Select line of plug wires,as well as caps and rotors, Pep Boys has 'em as well as Kragen out here in Reno. The best wires have spiral-wound metal conductor core,not solid wire or graphite-impregnated fiberglass core...all the hi-end wires like Jacobs,MSD,Taylor, etc., use this construction. The rotten gasolines available today make having a hot spark super important... Al the other posts on this were great, just don't overlook this one, Thanks!!!

bud L.
It is a single barrel carb, not really sure about the dual plane manifold, is there any clues how one looks like to help me identify it? (Sorry i don't know too much about engines in general).
I also heard once someone mentioned the ESA spark advance computer, could the ESA have anything to do with my problem?

a different slant,
thanx for your suggestion, i'm actually planning to get better set of wires, since the ones i have right now are set of plain-jane regular cheapos.

I was under the impression the ESA had been removed. It can't really cause problems if it's not there. If it looks like the one on my '86 Pick-up, it's black plastic, a little bigger than a cigar box, with a coupla dozen wires going to it, and a vacuum line connected to a vacuum canister attached to it.
If it is a single barrel carb, I doubt you have a dual-plane int manifold.

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'66 Cuda 225/4spd
'66 Dart GT convertible 225/auto
'64 Dart GT 340/4spd

Ok, i have a good news/bad news scenario:
The mechanic who works on my van has determined that the last three spark plugs are bad, because when they het-up they don't work very good.
So he changed all plugs to Ac Delco and warmed it up.
Then he tested by pulling the plug wires off the problem cylinders and suddenly they all worked right, so he called me with good news to pick it up.
I got the van and went for a little ride, stopped at the grocery store after about 15 minutes of driving and decided to take off the doghouse and perform the wire-pulling test again.
To my dissapointment my old problem was back.
I callec the shop right away and the guy told me to bring it in the next day morning so he can take a look at it.
So in the meantime i'm trying to figure out what went wrong and why are the last 3 plugs getting so hot, to the point of failure.
Oh, BTW when i was picking it up, he also mentioned that it has two timing marks on the pulley, which is kind of un-usual, so he has tried them both and somehow has determined which one of them is the right one.
I have also told him about the valve adjustement, but i guess he tought that he found the problem , before he could get to pull the valve cover.
Will be interesting to see what will happen tihs morning.

Your problem could be low coil voltage. This will cause engine misses at idle especially idling in gear with lights and ac on high. A common cause of this are those cheap rebuilt alternators or an under size alternator.
Good luck
D150

Guest, that also has crossed my mind but the misfires aren't random, they are consistent in #4/5/6 cylinders.
That kind of makes me think that there is something else going on.
Well, the sparkplugs got changed again this morning and it didn't help.
Actually when the eng. isn't too warm, everything works just fine, but after about 10 min. driving the last three cylinders aren't doing anything, when i perform the slow idle test by pulling the wires.
Actually i would be incorrect saying that they don't work at all, because when i for example pull #5 wire at idle and than give her some throttle the engine does start shaking, like it is missing that cylinder's work.
Same goes with #4 and 5.
So i have determined it only happens at idle, but still it shouldn't happen.
My mechanic has re-adjusted the timing to 16 degrees from 10, and still didn't do anything.
We're beginning to think that there might be something going on inside the carb, or the manifold itself.
Maybe the int. manifold's side with #4/5/6 cylinders is clogged-up with something, but once the pressure increases with more throttle, it gets past the obsticle, so it runs fine.
Now here is another of my problems:
I have decided that i'm going to get a re-built carb and see what happens.
I have called a few parts stores, but they all want a number from my existing carb.
Ok, no problem, i call the shop where my van was being worked on and told the mechanic to give me the #off that carb.
The only # he could find was 4300046, so i called it into the part's shop.
It came-up as a Carter 4bbl carb in their computer, which obviously isn't the case.
They have whole bunch of single barrel carbs for the slan't 6, but since i don't know which year is my motor or manifold, or even if it is the right carb in the first place, my guess is as good as theirs.
Problem is, that once i put it on and find out it's the wrong one, i can't return it anymore.
So i decided to take the cheaper route and get me a re-build kit for 1987, since the top-end appears to be newer than the block, but they still had 2 choices in 1987 kits.
So i flipped a coin and went with the cheaper one, see what happens.
Of course i have no idea what i'm getting, but chances are that the mechanic can identify if that is the right one, before even having to put it on, so i can return it.
The kit will arrive on monday, possibly installed by tuesday.
Lesson learned?
Never again i will buy a vehicle with non-original, mis-matched parts and mysterious wiring job, no matter how attractive the price is, specially since my knowledge of engines is somewhat limited.

The seven digit number from the carb sounds like a Chrysler part number. I don't know for sure, but it sounds like a late '70 or early '80's PN.
No offense, but your mechanic doesn't seem real in tune with an older Mopar with problems. Maybe, there is someone else in your vic. who might be more adept in sl/6, and old Mope. You need someone who doesn't need a scanner to diagnose stuff.

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'66 Cuda 225/4spd
'66 Dart GT convertible 225/auto
'64 Dart GT 340/4spd