So now my rig is backfiring (1 Viewer)

[SmokingRocks]

Background;

The following items have been replaced;

• denso fuel pump
• oem fuel filter
• oe fuel pressure regulator
• denso wires
• denso cap and rotor
• new spark plugs per spec (one year ago / 10,000 mi)
• injectors were cleaned, refurbished and flow matched
• new 2-1 magnaflow cat and flowmaster muffler
• replaced main engine harness

After all of that she ran great, more power, more response. just happy happy.

So last night I realized that if I let off the gas quickly the exhaust would pop a couple times. Not a loud back fire but a back fire indeed. Also idle is rough now, and it seems to be down on power (thats always hard to judge because theres never been a lot of it).

This is driving me nuts though, she should be tip top after all this work. And with the long drive to cruise moab coming up next week I'm at my wits end. My plan is to get my timing light out and see if I am not getting spark to a cylinder and then try to figure out why. If they all appear to be getting spark I guess I will pull the plugs (pulled #5 about two weeks ago and it looked a.o.k.).

I'm starting to lose hope. Anyone have any suggestions?

 

[BlueCruiser84]

Timing? Forget to tighten down the distributor?

Easy enough to double check.

 

[whitey45]

Check engine light? Vacuum leak, headgasket, common to get internal water leak into combustion chamber and causes an intermitant misfire. Also common to overlook and replace everything else!

 

[SmokingRocks]

idk about the CEL, theres no bulb. I just replaced a ton of the vacuum hoses will check again. Headgasket........ god I hope not, I'm not losing coolant thought. Guess I should pull plug 6 and see what condition its in.

 

[SmokingRocks]

And the timing was adjusted months ago. But i'll double check.

 

[SmokingRocks]

So I guess my Denso wires have a break in them around the cap... I just went out there after having her idle for about 20 mins and played around with the wires (I could hear it missing). then I figured it out, i took about 5 or so shocks through my right hand to my left hand resting on the body.... Looks like theres an issue with my wires or the cap.

Ouch... its been a bit since I've been hit by electricity haha.

 

[Reelitchy]

Maybe check the dashpot.

 

[BlueCruiser84]

Nice. Get some OEM ones!

 

[SmokingRocks]

those are $$$$ I ordered some NGK's. The denso's will be sent back for a full refund.

 

[BlueCruiser84]

Not cheap, but I just changed the original ones off a 1995 motor. They were still working great

 

[SmokingRocks]

OK so here is an update:

I replaced the Denso's with NGK's. Where the denso's had about 3" extra in length making them too long the NGK's could have used another .5" atleast... But they fit much better.

Anyway while I had the wires out I took the cap off to inspect the rotor. I figured that since I replaced those with Denso's there could be an issue there. Everything inside the cap looked completely fine, no signs of impeding doom, everything was clean. So I put it all back together and fired her up. I swear it was still missing a cylinder on idle, but if I rev'd it a bit it would settle down like it was firing on all 6. But it seems fine since I pulled it out of the garage last night.

I'm going to keep my timing light in my rig so that if this happens again I can see if I'm losing spark and to what cyl.

So to recap;

1. my rig was missing a cylinder and when I would let off the gas I would hear some pops out of the exhaust indicating that fuel was making it to the cylinder but not spark. (Also the engine harness was just replaced with a functioning unit and was heat wrapped at EGR)
2. Then I was messing with the wires at the cap while the rig was idling and I got electrified, which I took as bad wires (recently replaced Rock Auto Denso's, couldn't find any breaks upon inspection). So I ordered new NGK's
3. Installed NGK's last night, thought that the cylinder was still missing so I moved the wires around on the cap and it settled down.
4. Haven't had enough time to say if that was my fix or not.

My next steps would be;

• Pull and check / replace spark plugs (only have 10,000 mi on them?)
• revert to the cap and rotor that were previously installed
• start thinking about the ignition coil since this is the only component that has not been replaced. However I've always thought that a failing coil is either works or not.

Oh and I'm not losing coolant, the coolant is clean and clear & no bubbles in overflow tank.

Am I missing something here? Anyone have advice?

 

[SmokingRocks]

no one?

 

[elhombre]

Did the back fire problem go away? These cruisers are famous for having an intermittent miss at idle, but it goes away and has no effect when driving down the road.

 

[SmokingRocks]

haven't notice any popping. I'll replicate the situation on the way home.

 

[whitey45]

Check for misfire codes!! What year 80?

 

[SmokingRocks]

93

 

[SmokingRocks]

So I busted out the multi-meter and measured resistance to ground on each one of the wires. All of the wires to the plugs came back as 0's across the board. But the HT lead to the coil read 19.8 kilo Ohms, I removed the Lead from the coil and measured 19 kOhms at the HT lead output. Then I disconnected the supply wires and measured 2.18 Kilo Ohms on the ground side... of the connector to the battery.

Then I measured the resistance in the coil and got 12.67 Kilo Ohms from both the negative side to the HT side. So it looks like my ground is not great coming out of the coil, but what about the coil itself?

I am horrible with electricity... can anyone shed some light on this?