Intermittent miss up to 2k and idle when warm NA-T

[Travis89Turbo]

Originally Posted by pwpanas

I'd assume you didn't notice any cracks in the #6 piston's ring lands (this is common when compression is low). A bent valve is unlikely, unless your previous config was interference? A bent valve on the top side almost never happens with the OHC+bucket config. A leak tester is an excellent next step. Good luck with it, and please keep us informed. If I were to just guess (which I don't like doing), consider replacing your #6 piston (i.e. not the head).

Okay. Results of leak down.... I have only done cylinder 5 and 6 for the time being due to the cross over intake mani. And it was gettin late.

#5= an average of 25% leak. No leaking out of valves with small blowby past rings.
#6=an average of 85% leak! Blowing pressure out of intake and exhaust with very very little blowing by piston.

The ge is still Non interference motor but I'm assuming the added pressure from boost and high compression. May have tweaked them. It's not a massive bend cause it looked flush. I had done quite a bit of research before my tear down just tryin to find troubled areas on the GE. And like you said the cracks in the piston ring glands is a common problem. So I inspected the piston thoroughly and it besides the slight carbon (more then I expected at only 70k) the piston looked flawless as did the rings I pulled and measured within limits per factory manual. Although I replaced them anyways. The GE pistons are coated just as the GTE so I stayed away from the wire brushes.

I forgot to add that I found Volume 1 and Volume 2 of the factory service repair manuals on eBay for an insane deal of $45 shipped. Some were sellin for over 100+ These manuals are great. They cover everything you could think of and then ten times more! Thanks for the advice to pick those up!

[interested!]

Originally Posted by Travis89Turbo

Okay. Results of leak down.... I have only done cylinder 5 and 6 for the time being due to the cross over intake mani. And it was gettin late.

#5= an average of 25% leak. No leaking out of valves with small blowby past rings.
#6=an average of 85% leak! Blowing pressure out of intake and exhaust with very very little blowing by piston.

Hi! , The high blowby through the in and ex ports makes me believe the valves are on overlap - exhaust closing and inlet opening , may be an idea to retest with the crank in different positions to thoroughly test cylinder no 6 pressure .

[Travis89Turbo]

Originally Posted by interested!

Hi! , The high blowby through the in and ex ports makes me believe the valves are on overlap - exhaust closing and inlet opening , may be an idea to retest with the crank in different positions to thoroughly test cylinder no 6 pressure .

Only thing I can think of that is left would be ECU possibly. Hopefully I can talk my friend with the mk2 to let me swap ecus.

[interested!]

Hi! , No problem ! Question ? : is the engine a high miler from new without top-end overhaul ? -- The valve seats and valves may have some pitting and this is letting the pressure through , my 7MGTE head needed an overhaul ,the seats and valves desperately needed recutting/refacing following a BHG as they were severely pitted ,a leaking ( oil ) turbo and general clean-up . I've had two engines where the inlet valves have split at the seat and burnt away , one was nearly new , the other a high miler . both were misfiring .

[pwpanas]

Originally Posted by Travis89Turbo

Only thing I can think of that is left would be ECU possibly. Hopefully I can talk my friend with the mk2 to let me swap ecus.

How is your valve shim clearance?

Originally Posted by interested!

Hi! , No problem ! Question ? : is the engine a high miler from new without top-end overhaul ? -- The valve seats and valves may have some pitting and this is letting the pressure through , my 7MGTE head needed an overhaul ,the seats and valves desperately needed recutting/refacing following a BHG as they were severely pitted ,a leaking ( oil ) turbo and general clean-up . I've had two engines where the inlet valves have split at the seat and burnt away , one was nearly new , the other a high miler . both were misfiring .

True. I've seen a VERY badly pitted head from running higher boost on pump gas. In fact, (among other damage) it punched right through from one combustion chamber to the next! Lots of welding and machining was required to get that head back in shape.

[Travis89Turbo]

Originally Posted by pwpanas

How is your valve shim clearance?

True. I've seen a VERY badly pitted head from running higher boost on pump gas. In fact, (among other damage) it punched right through from one combustion chamber to the next! Lots of welding and machining was required to get that head back in shape.

I checked valve shim clearance and all were to the lower side of the limits per FSM.

Mileage is only 71,000. I purchased the car from an elderly man that was original owner. All factory service records.


I have an idea. Thinkin back a few post when I had pulled all my turbo stuff off and put the header on to determine which bank of cylinders was giving me trouble. I am wondering if its just the differential pressure between the rear bank that causes the ecu to go hay wire.

What if I weld an 02 bung pre turbo on one of the front bank cylinders to trick the ecu. I know this would cause 6 cyl. To run rich but it should keep the ecu out of lean mode. And the worse that could happen is I blow a motor that I am ready to pull out anyways.

Looking way back when I first bought my na header way before the turbo kit I noticed 6 cyl. Was not near as colorful (almost ss still) compared to the others. I think that has been a weak cyl. For a long time? But the turbo pushed it beyond the ecus threshold after the boost. It did run great and not skip a beat when I was running o2 on the front bank.

[pwpanas]

Originally Posted by Travis89Turbo

I checked valve shim clearance and all were to the lower side of the limits per FSM.

Mileage is only 71,000. I purchased the car from an elderly man that was original owner. All factory service records.


I have an idea. Thinkin back a few post when I had pulled all my turbo stuff off and put the header on to determine which bank of cylinders was giving me trouble. I am wondering if its just the differential pressure between the rear bank that causes the ecu to go hay wire.

What if I weld an 02 bung pre turbo on one of the front bank cylinders to trick the ecu. I know this would cause 6 cyl. To run rich but it should keep the ecu out of lean mode. And the worse that could happen is I blow a motor that I am ready to pull out anyways.

Looking way back when I first bought my na header way before the turbo kit I noticed 6 cyl. Was not near as colorful (almost ss still) compared to the others. I think that has been a weak cyl. For a long time? But the turbo pushed it beyond the ecus threshold after the boost. It did run great and not skip a beat when I was running o2 on the front bank.

If the #6 valves are bent, you could get 4 new valves, seat them with lapping compound, and then re-shim just those four buckets. *shrug* just brainstorming ... like you said, it's a good time to try options since you're at the point where the engine may have to come out anyway.

[Travis89Turbo]

Originally Posted by pwpanas

If the #6 valves are bent, you could get 4 new valves, seat them with lapping compound, and then re-shim just those four buckets. *shrug* just brainstorming ... like you said, it's a good time to try options since you're at the point where the engine may have to come out anyway.

Well here's where it gets even trickier. I was doin the leak down on the wrong stroke. I turned engine 180 and then leakage was in the 30s?? No blowby past the valves but some out of the bottom end past rings. The motor hasn't even ran enough for the new rings on 6 to seat. So now I don't think its a valve issue anymore. Lol. This dang thing.. I'm determined to figure it out.

What I did last night is pulled all the turbo equipment off and put my NA header back on with the ECU's Narrow band O2 sensors wired into the front bank. And then My AEM wideband in the rear bank. And wouldn't you know it. Ran perfect. Doesn't skip a beat or run rough at all. And like I was figuring the rear bank is running just slightly rich 13.4 vs before issue idle was about 14.5. I was able to run the engine up to operating temp hoping to help seat the new rings. Although I found my brand new cam seals are leaking like crazy so I am addressing that issue first today.. And I mean leaking bad. Wondering if I blew them out with leak down test? But not a big deal to change.

So what I am goin to do to for a more permanent fix is weld the o2 sensor bung into my number 1 cyl. Pipe on my turbo mani pre turbo to run my ecu. I got thinkin about tuning after that and figured the best way to do it accurately (except for 6) is to weld an additional o2 bung in either 1 or 2 for my wide band. Allowing me to tune accurately to 5 cylinders and 6 be slightly rich due to lower compression which may go up with some break in. Although it will technically only be tuning to one cylinder but the others are within a few psi of eachother and the low amount of boost/power I am aiming for and just daily driving it not beating it up I believe it should work.

Then the thought of passing the emissions smog test. Luckily its obd1 so its the sniffer. How I plan on makin it pass is with a separate tune I will add only for smog and load it to the ecu at the smog parking lot. Is move my wideband to the downpipe after turbo and de fuel the other cylinders to make My exhaust fall within smog limits. What do u think? To pass smog based off other vehicles I have tuned is around 14-14.7


I will be doin tune with MAP.ECU1 with built in map sensor and runnig an IAT sensor. Deleting MAF.

[interested!]

Hi! , Excellent news! just a bit of tweaking now , had us worried for a while .

[pwpanas]

Originally Posted by interested!

Hi! , Excellent news! just a bit of tweaking now , had us worried for a while .

Agreed.

Originally Posted by Travis89Turbo

Well here's where it gets even trickier. I was doin the leak down on the wrong stroke. I turned engine 180 and then leakage was in the 30s?? No blowby past the valves but some out of the bottom end past rings. The motor hasn't even ran enough for the new rings on 6 to seat. So now I don't think its a valve issue anymore. Lol. This dang thing.. I'm determined to figure it out.

What I did last night is pulled all the turbo equipment off and put my NA header back on with the ECU's Narrow band O2 sensors wired into the front bank. And then My AEM wideband in the rear bank. And wouldn't you know it. Ran perfect. Doesn't skip a beat or run rough at all. And like I was figuring the rear bank is running just slightly rich 13.4 vs before issue idle was about 14.5. I was able to run the engine up to operating temp hoping to help seat the new rings. Although I found my brand new cam seals are leaking like crazy so I am addressing that issue first today.. And I mean leaking bad. Wondering if I blew them out with leak down test? But not a big deal to change.

So what I am goin to do to for a more permanent fix is weld the o2 sensor bung into my number 1 cyl. Pipe on my turbo mani pre turbo to run my ecu. I got thinkin about tuning after that and figured the best way to do it accurately (except for 6) is to weld an additional o2 bung in either 1 or 2 for my wide band. Allowing me to tune accurately to 5 cylinders and 6 be slightly rich due to lower compression which may go up with some break in. Although it will technically only be tuning to one cylinder but the others are within a few psi of eachother and the low amount of boost/power I am aiming for and just daily driving it not beating it up I believe it should work.

Then the thought of passing the emissions smog test. Luckily its obd1 so its the sniffer. How I plan on makin it pass is with a separate tune I will add only for smog and load it to the ecu at the smog parking lot. Is move my wideband to the downpipe after turbo and de fuel the other cylinders to make My exhaust fall within smog limits. What do u think? To pass smog based off other vehicles I have tuned is around 14-14.7


I will be doin tune with MAP.ECU1 with built in map sensor and runnig an IAT sensor. Deleting MAF.

Thanks for the update! Please keep us informed.