Topic: D-series Misfire, Tried Everything (Read 7835 times)

enikolayev · « **on:** October 24, 2011, 06:36:14 PM »

The setup:
'92 Vx Chassis
D16Y8 block/head
eagle rods
srp pistons
supertech valvesprings/retainers
crower 2 n/a cam
hx35
Walbro 255 Inline
DSM 450's

Engine ran perfectly until i decided to track the car at Thunderhill. Overheated, blew a HG, cracked a piston skirt.
Tore apart the engine and rebuilt it, now i'm plagued with a misfire. At high rpm (6,500-7,000) it takes a little over atmospheric pressure to cause misfire. At low rpm (4,000) it will misfire around 3-4psi. In vacuum car drives perfectly.

O2 sensor reads 21 afr during misfire. I have also attached a video of the misfire while standing still.

Things I've tried:
Replaced Dizzy
Plug wires
new plugs, even tried gapping down to 0.020"
quadruple checked mechanical and ignition timing
adjusted valve lash
threw in the stock cam for shits and giggles
Hot wired the blk/yel wire on the dizzy in case it wasn't getting enough juice

I'm almost ready to put a 12Ga slug through the block.

Engine misfire

PhilStubbs · « **Reply #1 on:** October 24, 2011, 06:41:37 PM »

Have you done any logging? I would check that first.

enikolayev · « **Reply #2 on:** October 24, 2011, 06:46:28 PM »

I'm not sure what insight logging could give, the car won't accelerate during misfire.

snm95ls · « **Reply #3 on:** October 24, 2011, 07:50:50 PM »

That's a pretty sweet rev limiter you have there.

Joseph Davis · « **Reply #4 on:** October 24, 2011, 07:57:48 PM »

Do a leakdown, suspect a slightly bent valve or other leak (headgasket/cracked head/block).

PhilStubbs · « **Reply #5 on:** October 24, 2011, 08:27:48 PM »

Quote from: enikolayev on October 24, 2011, 06:46:28 PM

I'm not sure what insight logging could give, the car won't accelerate during misfire.

well, it sure as hell isnt going to hurt.

it can rule out a lot of things which would do a lot more than typing on a forum will

DasPoop · « **Reply #6 on:** October 24, 2011, 09:34:06 PM »

Quote from: Joseph Davis on October 24, 2011, 07:57:48 PM

Do a leakdown, suspect a slightly bent valve or other leak (headgasket/cracked head/block).

is it using using coolant? smokes? need some more info. what did the sleeves look like when you tore it down?

enikolayev · « **Reply #7 on:** October 24, 2011, 10:07:32 PM »

I'll do a leak down and report back. Cylinder walls had some scoring from overheating, the stone hone took most of the smaller scratches out, there's still a couple bigger ones left. I believe cyl 2 and 3 have scratches at the top two inches of the bore. Engine smokes a little bit, almost negligible and coolant level is constant.

chris · « **Reply #8 on:** October 25, 2011, 03:07:00 PM »

Is the dist a vatozone special or oem unit?

enikolayev · « **Reply #9 on:** October 25, 2011, 09:49:34 PM »

Quote from: chris M on October 25, 2011, 03:07:00 PM

Is the dist a vatozone special or oem unit?

Its an oem one from a buddies car.

HF leak down tester says 70%, 73%, 72%, and 75% Don't know how much I can trust HF tools.
Couldn't do a compression test b/c the tester broke, but after break-in the compression was around 175psi in all cylinders. Problem persisted ever since break-in.

Didn't hear any leaks through the exhaust, intake, and no bubbles in the radiator.

attached pic of spark plugs, this is from normal driving

PhilStubbs · « **Reply #10 on:** October 25, 2011, 10:02:40 PM »

Quote from: SecksyPeePee on October 24, 2011, 06:41:37 PM

Have you done any logging? I would check that first.

DasPoop · « **Reply #11 on:** October 26, 2011, 12:45:51 AM »

so you have 70+% leak down in all holes? sounds like you did more than just pop a head gasket. Start it up and take the oil cap off and see if you get sprayed in the face with oil. I am thinking under boost you are only hitting on 3 holes and the one that is hurt is the one that blacker plug came out of. Your putting pressure in the crank case and forcing it past your now scored to hell bores/busted ringlands

crttaz · « **Reply #12 on:** October 26, 2011, 02:36:18 AM »

with 70% leakdown you won't have 175 psi cranking.

15-20% leakage = 150-160 psi cranking.

You need 120 psi cranking for the engine to even run.

PhilStubbs · « **Reply #13 on:** October 26, 2011, 06:46:36 AM »

Leakdown tests are done at 80psi, I have a feeling he meant 70psi and not %.

enikolayev · « **Reply #14 on:** October 26, 2011, 06:40:11 PM »

Quote from: SecksyPeePee on October 26, 2011, 06:46:36 AM

Leakdown tests are done at 80psi, I have a feeling he meant 70psi and not %.

Quote from: crttaz on October 26, 2011, 02:36:18 AM

with 70% leakdown you won't have 175 psi cranking.

15-20% leakage = 150-160 psi cranking.

You need 120 psi cranking for the engine to even run.

I think the high reading can be attributed to both the large p-w clearance since this was done on a cold engine, and maybe to some degree the HF tester.

I'll do another compression test to confirm once i get another tester, but the car runs perfectly in vacuum. Even averaged 48mpg from Sac to Reno and back.

Quote from: SecksyPeePee on October 25, 2011, 10:02:40 PM

Quote from: SecksyPeePee on October 24, 2011, 06:41:37 PM
Have you done any logging? I would check that first.

You've convinced me.

Also, I'll check all the grounds on the ecu later this week.

chris · « **Reply #15 on:** October 26, 2011, 07:49:44 PM »

enikolayev · « **Reply #16 on:** October 26, 2011, 08:51:48 PM »

Quote from: chris M on October 26, 2011, 07:49:44 PM

cel?

No cel codes.

Just did the compression test. Pretty surprised by the results.

Dry: 205, 210, 210, 210
Wet: 210, 210, 210, 214

Sounds like a healthy engine internally.

Car was tuned with vitara pistons previously and had 150-155psi compression, could this contribute anything to the misfire problem?

chris · « **Reply #17 on:** October 27, 2011, 02:17:04 AM »

what map sensor is on there

Maybe try a stock and burn a new potato chip for a stock oem sensor

bigdaddyvtec · « **Reply #18 on:** October 27, 2011, 02:28:51 AM »

Headgasket.

I dont care what the leaky tyest or compression says.

My pile has done it.

Leakdown was spot on, HG was just compromised enough to were it wouldnt happen till the car started to warm up and it did EXACTLY what youre talking about.

FUCK YOU

enikolayev · « **Reply #19 on:** October 29, 2011, 04:20:53 PM »

Quote from: chris M on October 27, 2011, 02:17:04 AM

what map sensor is on there

Maybe try a stock and burn a new potato chip for a stock oem sensor

Tried this. Same story.

Quote from: bigdaddyvtec on October 27, 2011, 02:28:51 AM

Headgasket.

I dont care what the leaky tyest or compression says.

My pile has done it.

Leakdown was spot on, HG was just compromised enough to were it wouldnt happen till the car started to warm up and it did EXACTLY what youre talking about.

FUCK YOU

I have just replaced the HG. Sprayed a shitload of copper gasket spray on both sides, and torqued that bitch to 85ft-lbs. Can't be the HG.

Car refused to start shortly after being turned off today though. Opened the hood and wiggled shit around, then it fired right up. Weird.