I own a 99 1500 Ram. I am showing on my OBDII a cylinder 8 misfire. I have changed the Coil, wires, plugs, rotor, distributer cap. still showing the same problem.Any suggestions on what to do next would be appreciated.

Thanks

 

i was having the same problem.....i replaced all the things you did and still the light was on... days later, it went off, then came back on, then went off and has been for abouta week now. i have no idea what the problem is. so far i think its the weather. seriously. it started getting hot when the light came on, and now that its gotten cold again the light is off. if it pops up again when it gets hot, ill let you know

 

did you do a compression test on all your motor...that will tell you alot more...also could be a bad injector i would start with them 2 things and go from there...

 

Could be a few items: clogged injector inlet; cracked valve seat; or (very likely), a clogged cat.

 

doing a compression test is worth it
====
I did a compression test on my 1995 Magnum 5.9V8 this afternoon.

This engine was broken in for the first 18,000 miles with conventional oil and
switched to Mobil One synthetic. It presently has the Mobil One 15w-50 but
has used the 5w-30 and 0w-30 in the past.

Engine has about 142,000 miles on it.

I did the compression test because about 3000 miles ago my 2nd catalytic
converter plugged and created excessive exhaust backpressure - so much so that
the truck would not go above about 25 mph for the 8 miles it took to get to
the muffler shop. This excessive backpressure ruined the EGR modulating valve
diaphram, which was replaced, as was the O2 sensor.

I was worried I might have burned an exhaust valve.

The engine has been running 'ok' but seems to get slightly less mpg than
before.

I changed 2000 miles ago to NGK NGK ZFR5F11 (stock number 2262) just after the
bad cat, and the engine idle seems more uneven. Previous plugs were Autolite
3923.

In the figures that follow, 'Oil Added' means a squirt of Mobil One Gear Oil
75w-90 was put in the cylinder using a rubber hose on the end of the gear oil
bottle. The engine was cranked 5 revolutions and then the compression on that
cylinder was read again. It would have been better to have used a plunger
style oil can and put a consistent 3 shots into the cylinder. It might be
possible that the 'Oil Added' compression psi's are not consistent because the
amount of gear oil varied.

Engine was cool from sitting overnight.
Outside air 75 degrees.
Throttle bores were propped wide open during cranking.
All sparkplugs were removed.
Readings were taken on the 5th stroke and the compression tester had a
'shraeder valve' that held pressure on the gauge until pressed. Typical first
stroke compression numbers were around 100 psi and climbed to steady maximum
shown below by the 4th stroke.

Results:

Cylinder 1 - dry 145psi - oil added 175
Cylinder 2 - dry 145psi - oil added 165

Cylinder 3 - dry 150psi - oil added 185
Cylinder 4 - dry 155psi - oil added 185

Cylinder 5 - dry 155psi - oil added 180
Cylinder 6 - dry 150psi - oil added 170

Cylinder 7 - dry 160psi - oil added 175
Cylinder 8 - dry 148psi - oil added 165

Average dry: 151 psi
( # 7 is 6% high, # 8 is 2% low)

Average Oil Added: 175 psi
(#3&4 are 6% high, #2&8 are 6% low)

Additional information:
All 8 NGK sparkplugs looked clean after 2000 miles of mostly interstate
driving and had extremely white insulators on the relatively long 'projected
tips' of this design plug. Cylinder 6 had just bit different looking deposits
on the ground strap electrode - the other 7 plugs grounds looked normal 'dry
flaky' and this one looked slightly 'greasy'. When I changed out Cylinder 6
on the Autolite 3923's used previously cylinder 6's white insulator had more
black carbon deposits on it and looked just a bit oily. At the time I took
this to be because I had just sprayed a can of Mopar Combustion Chamber
Conditioner into the engine.

Engine does not seem to be using any coolant. Oil consumption is about 1
quart every 2000-3000 miles and there are slow drips from both front and rear
engine crankshaft seals.

Cylinder 7 may have more carbon deposits. I had previously found some time
ago that spraying Mopar Combustion Chamber Conditioner in cylinder pairs 7&8
got rid of pinging temporarily, maybe the problem is just cylinder #7.

The 1995 Ram FSM is not too helpful on what 'proper' compression readings
should be - it just says 100 psi on page 9-108 of my model year 1995 book.

This 100 psi seems to me like a 'cop out' number from DC listed to counter
angry customers who have a low reading cylinder. Or perhaps it is an
unchanged 'carry over' spec from 1978-1984 LA 360 V8s that had only 8 to 1
compression?

This 360 V8 engine is supposed to have a 9.1 to 1 compression ratio, as listed
on FSM page 9-81. {I hear later model 1996+ 5.9V8s were lowered to 8.9 to 1
compression ratio because of numerous owner pinging complaints.

On page 9-142 the 1995 FSM says the 1995 8.0L V10 with 8.4 to 1 compression
ratio is supposed to have 170-190 psi compression test numbers. Go figure?

The Engine Analyser 3.0 software from Performance Trends estimates that a 1995
Magnum 5.9V8 engine with 9.1 static compression ratio and the cam specs in the
1995 FSM should have 180 psi 'theoretical' cranking compression

Since I had everything out, I re-did the dry compression test on all 8
cylinders this morning after letting the engine fully warm up for about 30
minutes. Coolant was showing about 185 degrees.

All the cylinders increased by 5 psi versus yesterday's cool engine
measurements.

So my average went up to 155 psi and no cylinder varied more than about 5%
high or low. Yesterday the addition of oil jumped all the reading about 20
psi more.

In this month's Car Craft Steve Dulcich did three warmed up engine compression
tests on a 400 hp 9:1 Chevy 350 engine.

First one on worn engine rings that had done 100 dyno runs and the compression
test ran 160 psi.

Second test Steve did on brand new file-fitted conventional rings ran 165 psi.

Third test was on the 'Total Seal Gapless Rings' and those ran 185 psi.