4 Wheel Parts
4WD
ALLDATAdiy
JC Whitney
Off-Road Tires
Dodge Parts


Author Topic: backfires under power has me stumped  (Read 2707 times)

0 Members and 2 Guests are viewing this topic.

Offline I8A318

  • Newbie
  • *
  • Posts: 199
  • Gender: Male
backfires under power has me stumped
« on: May 14, 2012, 09:06:16 PM »
86 RC 2wd with 1988 - 318 2brl auto. Thursday the week before last i put in $60 worth of gas then the next day i topped it off at another station. i drove the truck about 60 miles and it than began loosing power / hesitating / and popping through the carb / and backfiring out the exhaust. the side pipes where extremely hot and stunk of gas. i suspected water in the fuel so i opened up the top of the carb and pulled the fuel filter. i found no water in the bowl or filter. i checked the timing ( it is set @ 12* BTDC ) just as the emission sticker call for. i then checked the distributor cap. all look good. so i decided to rebuild the carb. i then found water in the base plate only. i did the rebuild anyway. installed it and set it up. it starts and runs great when cold but when it reaches operating temp it starts with the backfire and hesitation again. it has great throttle response when cold or hot so i don't think the problem is the carb anymore. after work tonight i used sea foam on the carb / intake and used the PCV vacuum hose to suck the sea foam into the eng. i was even thinking it may have a sticking valve. when i pulled the spark plug from #1 cylinder it was completely covered in soot. they are fuel fowled as i expected from the sea foam and will need to be changed. this will have to wait until this weekend. has anyone run into this issue before? i looked around the site a little but nothing seems to fit exactly what my truck is doing.
about 2 1/2 years ago i replaced the entire ignition system. everything from the dis. / coil / ECC / plugs / wires and so on. i have only put on about 20k miles since with regular oil changes so i don't think its internal. i has great oil pressure hot or cold and there is no lifter chatter. i also checked the intake and vacuum lines for leaks and found nothing wrong.
any thoughts? is there something i am missing?  {think}     
86 ram charger se 2wd 5.2 auto
my wife yes / my dog maybe / my dodge never

Offline ToxicDoc

  • Lifetime Supporter
  • RCC Nut
  • *
  • Posts: 10129
  • Gender: Male
  • RCC Rules!
Re: backfires under power has me stumped
« Reply #1 on: May 14, 2012, 10:18:35 PM »
may or may not have to do with the fuel fill.  the plugs might have already been starting to foul up.  Regardless, if they are fouled, you really can't (and shouldn't) proceed to other diagnostic considerations.  replace plugs if fouled then check operation.

How many miles on engine?  Was timing steady? (sometimes worn out timing chain). check vaccum.
'85 W150 SB, 408 stroker, Magnum manifolds, Performer RPM, 670 Truck Avenger, HEI ignition, Auburn LSD 9.25 and '82 D44 (non-CAD) with 3.55/3.54,  NV4500/NP241

Offline Mike Barf

  • Lifetime Supporter
  • Mopar Nut
  • *
  • Posts: 6873
  • Gender: Male
  • Ker Chow
Re: backfires under power has me stumped
« Reply #2 on: May 15, 2012, 03:13:10 AM »
who did the carb conversion on the engine, 88 318 was throttle body injected,

was it doing this only under acceleration? or continuos when hot?

mine does the same thing under heavy acceleration and above 3200 rpm,    factory 88 360 with near on 200k on the clock.
88 RC, 360 auto 4x4 stock

 welcome to the service dept.
 you may choose any 2 of the following options
 cheap
 fast
 good,

 please any combination, you may not receive all 3 unless you are very deserving as decided by the staff.

Offline 340SHORTY

  • Sr. Member
  • *****
  • Posts: 4101
  • Gender: Male
  • on a steep hill
Re: backfires under power has me stumped
« Reply #3 on: May 15, 2012, 03:41:49 AM »
Read again Mr Bafr, he said 86.   

In my experience popping under accl is signs of a cam going bad... 
Your truck info goes here...

Offline Mike Barf

  • Lifetime Supporter
  • Mopar Nut
  • *
  • Posts: 6873
  • Gender: Male
  • Ker Chow
Re: backfires under power has me stumped
« Reply #4 on: May 15, 2012, 03:49:09 AM »
says 86 rc with 88 318… 88 , 318 is tbi.. can be converted.

  was there a check for timing slack/slop?  pull the cap and turn the crank by hand … any delay in rotor movement means timing slop,
  when you put the timing light on it does the mark jump at all?
  compression test?

  can of "heet" or "heat" or what ever water treatment for fuel ..
     if it is water in fuel it could help.
88 RC, 360 auto 4x4 stock

 welcome to the service dept.
 you may choose any 2 of the following options
 cheap
 fast
 good,

 please any combination, you may not receive all 3 unless you are very deserving as decided by the staff.

Offline Captain Obvious

  • Sr. Member
  • *****
  • Posts: 3553
  • Gender: Male
    • How to find truck help fast
Re: backfires under power has me stumped
« Reply #5 on: May 15, 2012, 03:52:21 AM »
Read again Mr Bafr, he said 86.   

1988 - 318 2brl auto.

Sure he did.

but yes on the camshaft/valve train.

There is a few ways to check depending on what you are comfortable with.

You may be able to physically spot something not looking like the rest.
You can do a dial indicator test to check lift.

Or....

You can do a compression test while the other 7 cylinders are running. This will actually tell you pretty fast which cylinder has bad valve train, and which side (exhaust or intake) the bad valve train is on.




One more thing. Your timing light shows 12ºBTDC...how do you know that line on the balancer is actually correct and has not slipped?
« Last Edit: May 15, 2012, 03:54:39 AM by Captain Obvious »

Offline I8A318

  • Newbie
  • *
  • Posts: 199
  • Gender: Male
Re: backfires under power has me stumped
« Reply #6 on: May 15, 2012, 05:45:00 AM »
when i checked the timing it was a steady 12* @ 750 RPM @operating temp. it starts backfiring around 2500 - 3000
in gear under power and will worsen as it throttles up. it also will sometimes backfire if you stab the gas from idle. i will be replacing the plugs this weekend. i did not check for lash yet but the timing chain was replaced when i installed the eng along with the oil pump. the eng had 100k on it when it was installed. the last comp. test was done when it was installed. it was 2 1/2 years ago so i do not recall the exact comp. the truck has not used a drop of oil since it was installed and it does not smoke. it was so nice when i installed it that there was still hone marks on the cylinder walls. also the eng came from a 88 Fifth Ave. it was electronic carb lean burn. not a TBI unit.
i did not mention this in my original post but the carb is a Holly 2280 non electronic. should i be running the spark plugs the emissions tag shows for the 86 truck eng? everything on the eng is based on an 86 RC 318. or should i be installing plugs that would be for an 88 fifth ave 318 as this is the eng that is in the truck?
thanks for any help on this.
86 ram charger se 2wd 5.2 auto
my wife yes / my dog maybe / my dodge never

Offline Captain Obvious

  • Sr. Member
  • *****
  • Posts: 3553
  • Gender: Male
    • How to find truck help fast
Re: backfires under power has me stumped
« Reply #7 on: May 15, 2012, 06:16:23 AM »
the last comp. test was done when it was installed. it was 2 1/2 years ago so i do not recall the exact comp. the truck has not used a drop of oil since it was installed and it does not smoke. it was so nice when i installed it that there was still hone marks on the cylinder walls.

Or....

You can do a compression test while the other 7 cylinders are running. This will actually tell you pretty fast which cylinder has bad valve train, and which side (exhaust or intake) the bad valve train is on.


A running compression test is different. It has nothing to do with the oil consumption/hone marks/rings. It is testing the breathing capability of the valve train while the engine is actually running.

Here is a bad video showing one being done while an engine is running.

Running Compression Test (Good)


They didn't cover all the steps like working the throttle under load, etc but nonetheless you can see the engine running with a gauge in it.

If you think you have a valve problem, and describe it as worse under load, it only makes sense to do that test. It's actually 3 tests. A normal compression test with all the plugs removed and throttle wide open, then a running test with 7 cylinders running at idle, then a very fast throttle blip. Those 3 numbers combined give you the whole valve train story. Normal test is for overall health and is the highest number. Running test number is much lower since engine is under vacuum and doesn't have as much air. Then the blip of the throttle momentarily fills up the cylinder. From there you can tell if you have a valve train problem on the exhaust or intake side. Not just a leak, but:
*carboned valves
*inlet restriction
*exhaust restriction
*pushrod/lifter/rocker issue that causes lash
*worn lobes etc

Offline Mike Barf

  • Lifetime Supporter
  • Mopar Nut
  • *
  • Posts: 6873
  • Gender: Male
  • Ker Chow
Re: backfires under power has me stumped
« Reply #8 on: May 15, 2012, 06:20:53 AM »
so .. holly carb swap….

 did you change/ remove the lean burn or will it actually work properly with the holly on there?

 what does the timing read at 2000 rpm?

 also.. do a compression test,

 there are many factors that can ruin engines in 2 1/2 years..

 also .. what kind of oil pressure are you getting?… a wiped cam bearing will ruin oil passage to the cylinder heads, causing valve issues..   just one more thing to check…. hopefully this issue can be diagnosed with out a complete teardown.
88 RC, 360 auto 4x4 stock

 welcome to the service dept.
 you may choose any 2 of the following options
 cheap
 fast
 good,

 please any combination, you may not receive all 3 unless you are very deserving as decided by the staff.

Offline I8A318

  • Newbie
  • *
  • Posts: 199
  • Gender: Male
Re: backfires under power has me stumped
« Reply #9 on: May 15, 2012, 05:48:27 PM »
the holly carb was on the truck when i bought it in 04. according to everything i have read it is supposed to be there. when i installed the 88 318 lean burn eng.  i used only the long block swapping everything from my original 318. the oil pressure is 75 LBS cold 60 LBS hot and 40 hot at idle in gear. oil pressure does not fall off under a load.
A running compression test is different. It has nothing to do with the oil consumption/hone marks/rings. It is testing the breathing capability of the valve train while the engine is actually running.

Here is a bad video showing one being done while an engine is running.

Running Compression Test (Good)

They didn't cover all the steps like working the throttle under load, etc but nonetheless you can see the engine running with a gauge in it.

If you think you have a valve problem, and describe it as worse under load, it only makes sense to do that test. It's actually 3 tests. A normal compression test with all the plugs removed and throttle wide open, then a running test with 7 cylinders running at idle, then a very fast throttle blip. Those 3 numbers combined give you the whole valve train story. Normal test is for overall health and is the highest number. Running test number is much lower since engine is under vacuum and doesn't have as much air. Then the blip of the throttle momentarily fills up the cylinder. From there you can tell if you have a valve train problem on the exhaust or intake side. Not just a leak, but:
*carboned valves
*inlet restriction
*exhaust restriction
*pushrod/lifter/rocker issue that causes lash
*worn lobes etc
i will be picking up a new set of plugs this weekend. i will hopefully perform a more complete  compression test then. i will also look into a vacuum gauge so i can get a better idea whats going on inside the eng. thanks for all your help. i will let you know what i find out.
86 ram charger se 2wd 5.2 auto
my wife yes / my dog maybe / my dodge never

Offline Captain Obvious

  • Sr. Member
  • *****
  • Posts: 3553
  • Gender: Male
    • How to find truck help fast
Re: backfires under power has me stumped
« Reply #10 on: May 15, 2012, 05:59:50 PM »

Offline The Hoss

  • Full Member
  • ****
  • Posts: 1858
  • Gender: Male
  • One day at a time.
    • http://conan.ramchargercentral.net
Re: backfires under power has me stumped
« Reply #11 on: May 15, 2012, 06:54:04 PM »
Regardless, if they are fouled, you really can't (and shouldn't) proceed to other diagnostic considerations.  replace plugs if fouled then check operation.

 {agree}   Then you need to find out why there fouled. Also if all tune up parts are 2 1/2 years old, I would put em all on! Double check your not running a little too rich..........
Name: Corey

1979 RamCharger       360/727------Rusted Away
2002 Caravan  3.8L
1997 Acura       1.6L
1984 Magna V45-process of being bobbed

Offline dodgeboydanno

  • Newbie
  • *
  • Posts: 71
  • Gender: Male
Re: backfires under power has me stumped
« Reply #12 on: May 16, 2012, 09:04:57 PM »
I fought with a backfire/popping on my first Dodge truck for most of one summer.  Turns out, the NEW spark plug wires I had installed were junk.  Worked good for about 3 or 4 weeks and popping started. I never even thought about the wires because they were new.  After changing everything else, cam and timing chain included, my dad changed the wires because I refused to (they were new, can't be them) and it ran like a champ.  Like Don Garlits said: "Just because it's new, doesn't mean it's good"
If big is good, and more is better, then too much is just right!!!!
'90 Ramcharger 150 LE 4x4 318 auto
'83 Ramcharger Royal SE 2WD  318 auto
'87 W150 360 auto

Offline 340SHORTY

  • Sr. Member
  • *****
  • Posts: 4101
  • Gender: Male
  • on a steep hill
Re: backfires under power has me stumped
« Reply #13 on: May 17, 2012, 03:11:51 AM »
I am curious on how a wiped cam bearing could cause backfiring under load... 
Your truck info goes here...

Offline 85 Royal SE Prospector

  • Sr. Member
  • *****
  • Posts: 4836
  • Gender: Male
Re: backfires under power has me stumped
« Reply #14 on: May 17, 2012, 07:44:26 AM »
I am curious on how a wiped cam bearing could cause backfiring under load...
I wish I could say it couldn't. I've not seen it before but in this motor's case that is probably not it. Likely a roller cam.

I'd go with the simple first. If the carb didn't run well before, you rebuilt it and it runs better- why not replace the plugs? Next make sure that the choke does not stick and does not move improperly all the way through the throttle range. Good time to make sure the throttle plates aren't sticking.

The wires may be junk. There's about a possibility of a 3-5 in 8 failure rate on most cheap new wires right out of the box.
1985 Dodge Royal SE Prospector Ramcharger 318 4x4

Offline I8A318

  • Newbie
  • *
  • Posts: 199
  • Gender: Male
Re: backfires under power has me stumped
« Reply #15 on: May 18, 2012, 08:37:50 PM »
i installed the new plugs cap and bug this evening. it fired up and runs great. best i can figure when the water got into the carburetor it damaged something causing it to run rich. it fuel fowled the plugs. when i pulled the plugs out they where black and dripping with fuel. looks like i will have to change the oil again. too bad because i just did an oil change about 2 weeks ago. oh well sucks to be me. i ran it for about 30 min with no problem at all. i will have to do a little more adjusting to the jets but i think i have the main problem fixed. thanks for everyone's help with this.
86 ram charger se 2wd 5.2 auto
my wife yes / my dog maybe / my dodge never