misfires on 8 and 5 on a 2001 non-SAI Discovery

J

jastutte

Well-known member
Nov 10, 2009
468
75
i have been trying to eliminate the misfires on cylinders 8 and 5 for a couple of weeks now. when the misfires first started i was also getting EVAP codes.

so far, i have replaced the gas cap, the purge valve (using the Hyundai part), the coils, spark plugs and spark plug wires.

i am still getting misfires on cylinders 8 and 5 and occasionally 4.

is this a grounding issue or should i be looking at fuel injectors?

the only codes i'm getting now are all related to the misfires. p0308, p0305, p0300, p1300.

i'm not really sure where to look next.
 
J

jastutte

Well-known member
Nov 10, 2009
468
75
oddly enough it does not misfire at start up at all. in fact it does not misfire when idling regardless of RPM.

it seems to misfire upon deceleration the most.

i drove it yesterday and punched the accelerator and had no misfires until i was coming to a stop.
 
J

jastutte

Well-known member
Nov 10, 2009
468
75
JUKE179r said:
8, 5, 3, & 2 are all on one coil pack. Coil pack possibly going bad or bad wire connections at coil pack.
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so far only 8 and 5 are misfiring. that is why i replaced the coil pack originally.

i just went out and checked the codes again.

as of yesterday, 8 and 5 are still misfiring and now 6 has shown up for the first time.

is there a better brand of coils to use?

at this point, i'm tempted to throw on a good used set that I have just to see what happens.
 
J

jastutte

Well-known member
Nov 10, 2009
468
75
roverover said:
Odd that a different coil set would send the same misfire
I would do a leak down test
Click to expand...
are you thinking this may be a valve train issue?

i did forget to mention that after i did the gas cap, purge valve, plugs and coils the truck drove fine for two weeks with no misfires.

the misfires came back and then i did the plug wires with continued misfires on 8 and 5 again and now 6 for some odd reason.
 
mlnnc

mlnnc

Well-known member
Mar 23, 2008
267
31
Charlotte
Cylinders 8 and 5 are paired in the DII wasted spark ignition system. A problem with one of the two plug wires, or less likely one of the two plugs, can cause misfires on both cylinders.

Since your truck's misfires have occurred both before and after you replaced the coil it seems most likely it's a problem with one of the two plug wires or the plugs themselves. Have you carefully inspected both wires and both plugs? How old are the wires and plugs, and what brands are they?

A similar problem was reported on another DII forum within the last month or so by a person who lives here in Charlotte. In his case, the cause of the misfires turned out to be that the coil terminal end of the plug wire for one of the two paired cylinders misfiring on his truck was loose.

Always diagnose in order - simplest, least expensive solution first, escalating from there.

And no, the evap code has nothing to do with the misfires.
 
donniefitz2

donniefitz2

Well-known member
Sep 15, 2020
138
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Scottsdale, AZ
fitzventure.com
Mine did something similar (can't recall which cylinders). I started with the simplest, cheapest thing: plug wires. That cured it. Not super easy to install, but not as bad as many say it is either.
 
J

jastutte

Well-known member
Nov 10, 2009
468
75
mlnnc said:
Cylinders 8 and 5 are paired in the DII wasted spark ignition system. A problem with one of the two plug wires, or less likely one of the two plugs, can cause misfires on both cylinders.

Since your truck's misfires have occurred both before and after you replaced the coil it seems most likely it's a problem with one of the two plug wires or the plugs themselves. Have you carefully inspected both wires and both plugs? How old are the wires and plugs, and what brands are they?

A similar problem was reported on another DII forum within the last month or so by a person who lives here in Charlotte. In his case, the cause of the misfires turned out to be that the coil terminal end of the plug wire for one of the two paired cylinders misfiring on his truck was loose.

Always diagnose in order - simplest, least expensive solution first, escalating from there.

And no, the evap code has nothing to do with the misfires.
Click to expand...
i'll recheck all the new wires. they are Kingsbourne brand. the plugs are all the cheap Champion plugs and i confirmed they were all properly gapped.

it would be very odd that the new coils or the new plug wires would have the exact same issue that the old ones did but only on Cylinders 8 and 5. that is what has me confused.

on the plus side, my son and i can now remove and reinstall the intake plenum in an hour or less.
 
J

jastutte

Well-known member
Nov 10, 2009
468
75
donniefitz2 said:
Mine did something similar (can't recall which cylinders). I started with the simplest, cheapest thing: plug wires. That cured it. Not super easy to install, but not as bad as many say it is either.
Click to expand...

as stated earlier, i have installed new coils, new Kingsbourne plug wires and new Champion plugs. i am still getting the misfires on 8 and 5.
 
D

discostew

Well-known member
Sep 14, 2010
7,733
1,024
Northern Illinois
Unplug both the wires at the plug and measure resistance thru the whole circuit. If its open then you probably have wires crossed. What you really need is a spark checker and check for good spark at the end of 5 and 8 plug wires. Not expensive, looks like a spark plug with a clip to attach it to a ground.
 
J

jastutte

Well-known member
Nov 10, 2009
468
75
roverover said:
Did you cross 5 and 8 wires?
Click to expand...
i assume by "cross" you mean accidently switch them? i'll double check that but my son and i were pretty careful with the reassembly and the Kingsbourne wires have the plug number on them.

i have had no misfires on the truck for the past two days of driving.

this includes a mix if highway and stop and go driving around town.

the only change i made was to snug up the intake bolts. if this is what solves the issue, i'll feel both relieved and foolish.

i suppose it's time to finally buy a torque wrench. any brand recommendations?
 
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