Fuel pump question, low RPM stumble
12-21-2022 | 12:21 PM
#46
Rennlist Member
Joined: Aug 2005
Posts: 10,274
Likes: 348
From: I should be in TNT for Carnival!
You don't have to have the special lift table to take the engine out. My indy in Chicago area took mine out with jackstands, tranny jack and two post lift when we removed to change the motor mounts and all rubber bits that couldn't be accessed with engine in. $1900 for engine R&R.
12-21-2022 | 11:23 PM
#47
Advanced
Joined: Sep 2022
Posts: 53
Likes: 5
so far, from multiple different threads its been suggested:
-Mopar Combustion Chamber cleaner
-Swepco 502, a few hundred miles before oil change
-Liquid Moly engine flush
Anyone used the above? Im always hesitant using any additives like these
As I continue to send the pictures to other shops, the answers are all over the place. One common response unfortunately, theyre not interested in doing the work. Special tools apparently for doing the V8 timing chains, as well as a HUGE lift table needed to handle everything coming down and out as intended.
Follow up with a couple more today. One suggested that if the top end indeed needs to be done, he had concerns about the bottom end having 155k on it. I should consider getting a new long block from Porsche. A quick look shows NLA, but even if one was sitting on a pallet somewhere how $$ crazy would that be. Still feeling like Im going down a mis-diagnosed rabbit hole.
I need a shop to step up, and give me a second opinion on this. Ill just keep expanding my search for that shop outward I guess.
-Mopar Combustion Chamber cleaner
-Swepco 502, a few hundred miles before oil change
-Liquid Moly engine flush
Anyone used the above? Im always hesitant using any additives like these
As I continue to send the pictures to other shops, the answers are all over the place. One common response unfortunately, theyre not interested in doing the work. Special tools apparently for doing the V8 timing chains, as well as a HUGE lift table needed to handle everything coming down and out as intended.
Follow up with a couple more today. One suggested that if the top end indeed needs to be done, he had concerns about the bottom end having 155k on it. I should consider getting a new long block from Porsche. A quick look shows NLA, but even if one was sitting on a pallet somewhere how $$ crazy would that be. Still feeling like Im going down a mis-diagnosed rabbit hole.
I need a shop to step up, and give me a second opinion on this. Ill just keep expanding my search for that shop outward I guess.
12-25-2022 | 03:51 PM
#49
Thread Starter
Rennlist Member
Joined: Jan 2010
Posts: 4,968
Likes: 279
From: Oneida, New York
Update…found a shop that would tackle the head work, if needed. They agreed that initially they would work to confirm the diagnosis, before just ripping and tearing things out.
So, if the entire drivetrain is dropped out, not absolutely necessary for the heads, but if you add in the clutch/engine mounts…well then it’s easier to just put everything on the deck.
I already have all the clutch bits, and motor mounts…so I asked for just a labor estimate. No way of knowing all the “while your in there” top-end bits that would need to be replaced, once the heads were off. Initial labor only estimate was $6-7k. Honestly, if the top end did indeed need to be done…well it’s pretty logical that all the lifters and bits should be replaced also. That’s ALOT fo lifters for a 4 valve/cylinder V8…roughly $5k in additional piece’s parts.
So in a nutshell…not even a super high spec 6MT GTS is worth that kinda investment. Be in the $15k ballpark all in, with the clutch bits, and it still has 155k miles on it, and enough road rash to think that it was the track appliance for the previous owner, and not the tow vehicle for his track 911.
So, a plan B suggestion, and questions arose from there. Liquid Moly Valve Cleaner fuel additive was suggested, as well as a discussion on what fuel was currently used.
Everything close to me is now “Independent” fuel brands essentially, Circle K, Fastrac, Red Apple(Kwik Fill), Byrne Dairy…all used to have Mobil, Sunoco, Citgo. Now no fuel branding is shown.
I gave myself an education about “Top Tier fuels”, and was reminded of the old Mobil fuel tagline….Drive your car clean. I assume that the fuel that’s been run thru my GTS(Kwik Fill), has the minimum required detergent additive’s, and is not an aforementioned Top Tier fuel, with 2-2.5 times that recommended detergent level.
Added the first can of Liquid Moly valve cleaner into the tank, and gave her an Italian tune up earlier.
I plan on hammering the hell outta her for the next 5k miles, going with Sunoco 91 premium, and a can of that valve cleaner in every tank.
While the last parts thrown at her, plugs/coil packs, and HPFP did make a noticeable difference in the stumbling…it still idles rough, and stumbles at lower rpm’s. You can hear…and feel that stumbling.
What makes me believe that the diagnosis of the carbon build up, and subsequent valve seat deterioration as causing the mis-firing, and rough running is not correct…is how normal it feels/sounds at higher rpm’s.
From 4K rpm’s to near redline, she sounds and feels normal.
I have till June of 2023, until my State inspection is due again. If the CEL isn’t off by then, due to the better fuel/additive’s, and/or a trip to that Indy to get a second opinion…it’ll be time to step away.
Just a modern version of the ole “snake oil salesman “, miracle in a bottle/can
Season of miracles and all….I believe, I believe, I believe
So, if the entire drivetrain is dropped out, not absolutely necessary for the heads, but if you add in the clutch/engine mounts…well then it’s easier to just put everything on the deck.
I already have all the clutch bits, and motor mounts…so I asked for just a labor estimate. No way of knowing all the “while your in there” top-end bits that would need to be replaced, once the heads were off. Initial labor only estimate was $6-7k. Honestly, if the top end did indeed need to be done…well it’s pretty logical that all the lifters and bits should be replaced also. That’s ALOT fo lifters for a 4 valve/cylinder V8…roughly $5k in additional piece’s parts.
So in a nutshell…not even a super high spec 6MT GTS is worth that kinda investment. Be in the $15k ballpark all in, with the clutch bits, and it still has 155k miles on it, and enough road rash to think that it was the track appliance for the previous owner, and not the tow vehicle for his track 911.
So, a plan B suggestion, and questions arose from there. Liquid Moly Valve Cleaner fuel additive was suggested, as well as a discussion on what fuel was currently used.
Everything close to me is now “Independent” fuel brands essentially, Circle K, Fastrac, Red Apple(Kwik Fill), Byrne Dairy…all used to have Mobil, Sunoco, Citgo. Now no fuel branding is shown.
I gave myself an education about “Top Tier fuels”, and was reminded of the old Mobil fuel tagline….Drive your car clean. I assume that the fuel that’s been run thru my GTS(Kwik Fill), has the minimum required detergent additive’s, and is not an aforementioned Top Tier fuel, with 2-2.5 times that recommended detergent level.
Added the first can of Liquid Moly valve cleaner into the tank, and gave her an Italian tune up earlier.
I plan on hammering the hell outta her for the next 5k miles, going with Sunoco 91 premium, and a can of that valve cleaner in every tank.
While the last parts thrown at her, plugs/coil packs, and HPFP did make a noticeable difference in the stumbling…it still idles rough, and stumbles at lower rpm’s. You can hear…and feel that stumbling.
What makes me believe that the diagnosis of the carbon build up, and subsequent valve seat deterioration as causing the mis-firing, and rough running is not correct…is how normal it feels/sounds at higher rpm’s.
From 4K rpm’s to near redline, she sounds and feels normal.
I have till June of 2023, until my State inspection is due again. If the CEL isn’t off by then, due to the better fuel/additive’s, and/or a trip to that Indy to get a second opinion…it’ll be time to step away.
Just a modern version of the ole “snake oil salesman “, miracle in a bottle/can
Season of miracles and all….I believe, I believe, I believe
12-25-2022 | 05:39 PM
#50
Instructor
Joined: Dec 2021
Posts: 203
Likes: 44
How about getting a leakdown test done on #8 to see if the valve is sealing or not so you can rule that in/out? I only skimmed the thread but seems like nobody has even checked compression on that cylinder yet.
I once had an engine (iron block) with a mildly burnt valve which I was able to fix with an upper engine cleaner (I use the OEM Subaru one). Did a comp test before and after, something like 90 back upto 170psi.
On the Cayenne, I would be a little worried about where all that carbon will go when it breaks off and what it might do to our soft aluminium bores.... Hence the suggestion of a leakdown test first.
I once had an engine (iron block) with a mildly burnt valve which I was able to fix with an upper engine cleaner (I use the OEM Subaru one). Did a comp test before and after, something like 90 back upto 170psi.
On the Cayenne, I would be a little worried about where all that carbon will go when it breaks off and what it might do to our soft aluminium bores.... Hence the suggestion of a leakdown test first.
12-26-2022 | 08:55 AM
#51
Race Director
Joined: Nov 2006
Posts: 15,719
Likes: 1,455
From: Clifton, NJ
How about getting a leakdown test done on #8 to see if the valve is sealing or not so you can rule that in/out? I only skimmed the thread but seems like nobody has even checked compression on that cylinder yet.
I once had an engine (iron block) with a mildly burnt valve which I was able to fix with an upper engine cleaner (I use the OEM Subaru one). Did a comp test before and after, something like 90 back upto 170psi.
On the Cayenne, I would be a little worried about where all that carbon will go when it breaks off and what it might do to our soft aluminium bores.... Hence the suggestion of a leakdown test first.
I once had an engine (iron block) with a mildly burnt valve which I was able to fix with an upper engine cleaner (I use the OEM Subaru one). Did a comp test before and after, something like 90 back upto 170psi.
On the Cayenne, I would be a little worried about where all that carbon will go when it breaks off and what it might do to our soft aluminium bores.... Hence the suggestion of a leakdown test first.
12-26-2022 | 07:02 PM
#52
Instructor
Joined: Dec 2021
Posts: 203
Likes: 44
Yes. Most leaky/burnt valves start as a piece of carbon caught between the valve head and seat. The valve slamming shut a thousand times a minute eventually mashes the carbon into the seat or valve to the point of making a low spot that breaks the sealing ring.
In this case I caught it early enough that the cleaner was able to dislodge the crap before it fully damaged the seal surface.
In this case I caught it early enough that the cleaner was able to dislodge the crap before it fully damaged the seal surface.