tune up help

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zac_F71

zac_F71

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just did plugs, wires, cap, rotor, and fuel filter on my 87 Dodge D150 pickup 225 slant six (3.7L) and now it has a dead cylinder (No.5)-

No.5 wire is good (Mallory 8mm race wire) tested with old plug (gaped at .032") and had good spark in a thick orange color..

pulled the No.5 wire while it was running and made no difference is what I'm getting at- I'm planning on renting a compression tester today- AND get a new plug as I broke a new one putting it in.

it misses VERY bad under load (moving the truck) wants to and does die while driving and backfires out the exhaust.

every other plug wire pulled from both the cap and the plug it wanted to die- No.5 pulled from cap and the plug was no difference in idle quality but it has spark and fuel.

tried new plug and even a known good wire still the same..

also it does not run hot nor does it use coolant starts right up like it should but only with a miss fire out the exhaust

have not done compression test yet it is next on the list..
 
Could you have moved the pickup during the cap change? check your reluctor gap and reluctor ribs. Are you missing a vacuum line somewhere? Might want to bump the motor with the valve cover off and see if the #5 valves are moving.
 
If it did not happen before the new cap was on, put the other cap back on, I have bout new parts that was not good before, thus why I don't change anything unless it is bad..
I have bout a distributor cap and rotor that did the same thing and ran like chit, I just put my old one back on. What plugs did you use, and do you have drool tubes ?
If you have drool tubes I remove the washer.
 
pishta said:
Could you have moved the pickup during the cap change? check your reluctor gap and reluctor ribs. Are you missing a vacuum line somewhere? Might want to bump the motor with the valve cover off and see if the #5 valves are moving.
Click to expand...

X2 :cheers:, could be a bent push rod, This is a newer /. :tard: Could be a bad lifter and not pumping up.. I agree pishta, remove the valve cover and see if #5 is rocking as much as the others :D sorry..
 
memike said:
X2 :cheers:, could be a bent push rod, This is a newer /. :tard: Could be a bad lifter and not pumping up.. I agree pishta, remove the valve cover and see if #5 is rocking as much as the others :D sorry..
Click to expand...

i think that is a little far to dig when we dont even know if it was doing this before the tune up...
 
805moparkid said:
i think that is a little far to dig when we dont even know if it was doing this before the tune up...
Click to expand...
I agree, I was thinking he did a timing gear and chain replacement :eek:ops:
That was another thread I was on.. another brain fart by me memike :D
Thank you moparkid :cheers:
 
It was not missing to my knowledge but always had a hesitation off idle (that has never gone away even before the 71 carb/intake/exhaust manifold swap)and should also mention that it has no smog stuff (except the charcoal canister which is hooked up) AND most importantly it has a rebuilt Holley 1bbl off my 71 Demon..

it ran all last week and parked it for the weekend (didn't start it all weekend) did the tune up this morning and now it misses badly

intake/exhaust gasket was done 20k ago and is still good
should be no vacuum leaks
I will check the valves under the cover tomorrow
the timing gears and chain were done 20k ago also
timing is dead on 12-16*


I used Autolite copper (PN 26) gaped to .032" non gasket type plugs

the truck was not moved during the change nor is the firing order wrong, this has a smog head if you're referring to the spark plug tubes- it doesn't have them all metal surrounding the plugs

the cap is a Wells brand and was replaced by the same brand- it needed it but I will switch them out tomorrow before the compression test (it's first tune up in 50,000 miles (besides oil changes)
 
zac_F71 said:
It was not missing to my knowledge but always had a hesitation off idle (that has never gone away even before the 71 carb/intake/exhaust manifold swap)and should also mention that it has no smog stuff (except the charcoal canister which is hooked up) AND most importantly it has a rebuilt Holley 1bbl off my 71 Demon..

intake/exhaust gasket was done 20k ago and is still good
should be no vacuum leaks
I will check the valves under the cover tomorrow
the timing gears and chain were done 20k ago also
timing is dead on 12-16*


I used Autolite copper (PN 26) gaped to .032" non gasket type plugs

the truck was not moved during the change nor is the firing order wrong, this has a smog head if you're referring to the spark plug tubes- it doesn't have them all metal surrounding the plugs

the cap is a Wells brand and was replaced by the same brand- it needed it but I will switch them out tomorrow before the compression test (it's first tune up in 50,000 miles (besides oil changes)
Click to expand...


ok what i would do is just swap caps... if it runs better then you know your issue...
 
OK! I read and followed my Haynes manual to a "T" basically and all came back zero-

engine warm
pulled coil wire
pulled all 6 plugs and tested each cylinder in 3- 5 second bursts and 1- 10-15 second burst
All came back with "0psi"

tested 2 cylinders cold and came back with No.2 50psi and No.5 31psi

Also I should mention I checked the firing order and had the 5/6 wires on the cap switched so it now idles but just touching the gas and it misses sitting and under load
 
did another compression test with another tester and came back with..

No.1 150psi
No.2 150psi
No.3 150psi
No.4 140psi
No.5 120psi- tested with oil was 145psi
no.6 140psi
 
The compression readings are good enough that it shouldn't cause a miss. Being an '87, it could have computer or carb problems which are much harder to diagnose. I'd put a timing light on each plug in turn and see if it is an ignition miss to start with.
 
hmm I will try that tomorrow I'm also gonna read on how to reset the computer in it.. it has a 71 rebuilt holley 1bbl carb/intake/exhaust mani (off my 71 Demon)

I fixed the exhaust leak so I should be able to get something done lol
 
Bad ECU and or Vacuum leak, timing is not set or carb is in need of a rebuild...
resetting computer,, Never herd of such a thing, replace ecu.. Have you tried putting your old cap and rotor back on.
 
You have a '71 carb on an '87 computer controlled vehicle? "Houston, we have a problem"........
 
hahaha it's fixed TURNS OUT a TON of vacuum leaks you'd never guess...

vacuum tree on intake loose (if I hadn't touched it- never woulda known), plastic vacuum "T" hanging over intake was melted(now gone), loose carb (loose on intake), replaced any lines that looked old(fuel, PVC, and vacuum)

and the idle mixture was WAY lean

the Holley on it was rebuilt using a NOS kit off ebay- timing is set to factory 15*-16*

it's a little low on power but I'll play with the initial timing since I have the day off tomorrow
 
Same sort of thing happened to mine but not as bad.
Could not get a shake out at idle.
Turned out to be a loose intake/exhaust nut - tightened = problem solved. The same also happens when the carb mount bolt needs a turn.
Now I always check those first.
 
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