Random Misfire

[Brentbba]

Ok - and how do you access it to splice it? Perhaps a good inch thick? Runs back from the throttle body area up past the EGR pipe to the top of the firewall and then takes a sharp left over toward the PS of the engine bay and down and in to the ECU behind the glove box. From what I can see it looks in ok shape from the outside. A little heat shielding on the very top but not where it sits on the EGR pipe?

Any help - looks like removal of the coolant tubes, egr valve and modulator, etc. at a minimum to access this little section of wire???

 

[semlin]

Any help - looks like removal of the coolant tubes, egr valve and modulator, etc. at a minimum to access this little section of wire???

brent did you find it and inspect? i don't recall it being that big a problem to access and i think there is some slack. you might have to pull the throttle body and remove the modulator but that is not a big deal. the modulator is just clipped in and the throttle body can be moved out of the way after you remove the bellows, throttle and cruiser control cables and 4 bolts.

 

[semlin]

brent, try this. start the motor then start moving this part of the harness around and see if it causes you misfire issues

 

[Brentbba]

brent did you find it and inspect? i don't recall it being that big a problem to access and i think there is some slack. you might have to pull the throttle body and remove the modulator but that is not a big deal. the modulator is just clipped in and the throttle body can be moved out of the way after you remove the bellows, throttle and cruiser control cables and 4 bolts.

LOL! Not a big deal to you. Ask CDAN the next time you order parts about my engine mechanical skills! :whoops: I tend to break anything I try to remove!

Very little play at all in the wiring harness back there. It's tight

I'll try to move the harness some with the engine running tho.

FIL has an ignition scope we're going to hook up tomorrow afternoon. He's a lot more competent than I ever will be on engines, even at 87. He'll direct tomorrow and I'll to my best to break something anyway! Will also do the resistance tests with an ohm meter on the ingnition coil and do the same tests on the distributor and visually inspect it with the cap off as well.

Thanks for the pointers Semlin.

 

[Mo Rocks]

I inspected my wire harness on my "new to me" '94 last weekend. It looked more intimidating than it really was. I had already replaced the plug wires, plugs, cap and rotor, PCV & grommet, and related vent hoses and the big $$ intake hose with OEM ...thanks CDan.
I thought I was going to have to remove the EGR, Coolent lines,etc. But I was able to get adequate visual access to the wire harnes by:
1) Remove the 2 bolts holding the rear coolent lines and valve to the firewall.
2) Remove the metal clip holding the cable for the heat control valve. ( looks like a lawn mower throttle cable) It pops off easily
3) Remove the 2 bolts holding the black plastic wire harness cover on the firewall
4) Use a screwdriver to push the clips apart that hold the black plastic cover together. (several on the bottom) The cover slips off the harness at this point.
5) Remove the coolent line where it attaches to the rear of the engine. It is a simple spring clamp . With the coolent line off at this one point, I was able to maneuver the harness to just in front of the entire coolent assembly at the rear of the engine. ( just a little tricky...not hard, just be careful)
This gave me the clearance to slowly remove by (by hand) the factory insulation followed by the factory grey elect. tape.
I started above the point where the wires came in close proximity to the EGR...and worked towards the EGR. I just carefully unwrapped it...

Take your time. It is a one job. Luckily I found my wires to be intact. (One thing I do not have to worry about now) I reconnected the coolent line so I could start the engine and wiggled the exposed wires by the EGR to see if it made any changes in "my misfire".
I was not able to make any changes in my misfire pattern.

My misfire was discovered when I finally checked my timing and found it to be at 25-30 degrees advanced by the PO.....I am amazed it even ran.

My big PITA was getting the distributor back into the correct "tooth" I must have tried 7-8 times. It did not want to go into the right slot......PITA...
Finally got it and it runs smooth !!!!!!
I have my timing at 3 degrees advance right now.

I bought some 2000 degree heat shield tape (I think they call it Cool Tape) at Advance Auto. ($16.)
I will put it on Sunday...The IHRA Pro Mod drag cars are in town this weekend (tomorrow) !!!

So check your timing and dist. too.......

Good luck.

 

[Brentbba]

Mo Rocks and Semlin - thanks - FIL and I are tackling this tomorrow afternoon. He does have an ignition scope he brought down.

We'll try the harness wiggle test first before tackling anything else to see if that causes a misfire. You're ahead of me with what you've done in your first paragraph. I have replaced the big intake tube.

For me, I'll personally take a or more if we can actually figure this out.

 

[Brentbba]

Ok, here are our results. Harness appears to be fine. Vigorous movement of the harness back behind the EGR modulator and valve produced no change in the random misfire. Inspected the wiring at the ECU and jiggles those to w/o any change to the misfire. FIL had a new spark analyzer so he tested the 6 ignition wires and everything tested ok there. Removed distributor cap for a quick inspection for the FIL. No issues noted on visua to him - I don't know what the fawk to look for - no tool to test the gaps per the FSM.

We then connected his ingnition analyzer. 1973 Heathkit model still going strong. Here's the video:

YouTube - Engine Analyzer

Curious to see what you think. FIL has his opinion. Hint - watch carefully at the firing of 1 and 5 of the firing sequence 1,5,3,6,4,2.

 

[semlin]

that's cool but i have no idea what it means

 

[Brentbba]

that's cool but i have no idea what it means

LOL! You've got six lines and dashes there representing the six cylinders. When all are firing, you see all six lines, dots and dashes. Watch very carefully at the first and second lines. Those represent the #1 and #5 cylinders. They disappear occasionally meaning that they are not firing at all in that sequence as they should. Pay close attention or you miss it. I sat looking at the CRT for quite awhile before I noticed it. It's not regular, an sometimes just the #1 cylinder. On a few occasions it was the #1 and #5 together. Rarely and not while I was taking the video, it appeared to be #1, #5 and #3 all at once. Looks like the distributor may be the culprit.

I shook the hell out of the harness and nothing ever happened.

 

[semlin]

missing on multiple cylinders makes me wonder if they messed up the timing advance by putting the dizzy in a tooth off. i did that after the hg job and it ran very badly.

 

[Brentbba]

missing on multiple cylinders makes me wonder if they messed up the timing advance by putting the dizzy in a tooth off. i did that after the hg job and it ran very badly.

Hmmm...interesting. Thx. Worth having that checked before feeding Dan's dogs for a new one, that's for sure. One thought tho - if the distributor was off a tooth, wouldn't the miss I see on the scope be consistent instead of random as it appears to be?

 

[Mo Rocks]

Hmmm...interesting. - if the distributor was off a tooth, wouldn't the miss I see on the scope be consistent instead of random as it appears to be?

My engine misfire was random...or at least it sounded like it was random....but then I did not have a 1973 Heathkit scope to check it out with....

Point being...my dist was off by a tooth....I discovered it by checking my timing with a 1970 Sears Craftsman timing light.

My timing mark was way off the scale...I est. it was at least 25-30 degrees advanced.

It runs nice and smooth now that I got it back into the right tooth space.

Might be worth checking out....and a good time to R&R the dizzy O-ring while you are there.....

 

[Brentbba]

I discovered it by checking my timing with a 1970 Sears Craftsman timing light.

Love it! They dont' build things like they used to do they!

 

[Brentbba]

Bump for any other diagnosis from the engine scope video in post #27?

 

[Brentbba]

Getting as frustrated as wildman326 in this thread. https://forum.ih8mud.com/80-series-...ng-out-no-codes.html?highlight=random+misfire Big difference is that mine is noticable at idle and not at speed. Hoses in the vacuum system all look ok and the big intake tube is less than 2 years old and still very plyable.

BIL had the gap measurement tool so I borrowed it and took the dist cap off again this morning. Tested the NE pickup and the gap there is within specs. I don't own a socket big enough to rotate the crankshaft pully to align the pickup coil projections at G1 and G2 pickups so those gaps are still in question. Ohm meter confirms that the pickup coil resistance is in specs at NE, G1 and G2 on the dist.

Ignition coil resistance on secondary and primary coils are both within specs.

I don't own a timing light to see if timing is really ok or if the shop that did the HG has just blown me off because that's the way I'm feeling. Per them the HG job is fine and can't figure out what's going on with the misfire that's occured SINCE the HG - never before.

I hate to just start throwing $$ at it with new spark plug wires (they are new from Aug '09) or a distributor housing (it's 16 years old - original). Cap and rotor are also new from Aug '09 and the spark plugs themselves are brand new twice since the HG. Another visual inspection of the inside of the cap shows nothing.

I'm ready to just take a sledge hammer to the fjawing engine to vent my frustration, part out everything else on the cruiser and by an FJ Cruiser. FAWK! Last chance for this engine's redemption is a trip to Yotamasters June 9th or a plane ticket for Robbie!

Outside of replacing the spark plug wires, distributor housing, cap and rotor, I dont' know what to do. It's been a random misfire so far, but it's getting worse and more prevalent, but not what I'd call consistent yet.

 

[Michael Hanson]

How old is the fuel pump? MIke

 

[Brentbba]

How old is the fuel pump? MIke

Original - No issues tho when I'm accelerating and the engine is in need of more fuel. Don't think the fuel filter has ever been changed either.

 

[semlin]

did you check the timing?

 

[Michael Hanson]

Fairly cheap and easy fix,these cruisers need consistant pressure ,this I think would contribute to the random nature of the problem. 2 cents MIke

 

[Brentbba]

did you check the timing?

I haven't - don't own a timing light, but it's one of the things I'll have Yotamasters do. At this point relying on statement from HG folks that the timing is right on Semlin.