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Severely missing after timing belt change

 
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bureau13  



Joined: 07 Sep 2017
Posts: 67
Location: South Florida

PostPosted: Mon Jan 22, 2018 3:55 am    Post subject: Severely missing after timing belt change Reply with quote

So I finished my timing belt job...timing shouldn't have changed, cam and crank gears line up properly, etc. I didn't touch the distributor, or anything like that. The car started right up, but sounds like it's running on three cylinders most of the time. Every so often, it will smooth out at idle (or steady-state cruising) and you can feel it as well as hear it, but it always goes back to the misfire state. Also, when driving, whenever I give it gas, it misfires, and I can feel it holding back.

Here's a short video of idle, showing both states:

https://photos.google.com/share/AF1QipNp-UKApn-xwCiEPEAY9pInSDOZYaRUHwAK6JUrkDtjdDxs76q3bmCPBFr_mqYQ2A?key=OVhsR21lVlBfMXBZRTVPR1VoTkdHVzF1dHM2d2Fn

Any ideas?
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1534
Location: Somerset, UK

PostPosted: Mon Jan 22, 2018 7:26 am    Post subject: Reply with quote

If the old belt was a tooth out on the cam and timing was cock on then it would have ran relatively OK (advanced cam timing brings on turbo early but runs out of legs at the top end, retarded cam gives more top end on a turbo at the detriment of the early onset of boost)

If the new belt has rectified this issue with the tooth it would have knocked out the timing

Continental belts are known to be 1/2 tooth longer than Gates/Dayco which can knock out the timing

Timing needs checking regardless
_________________
1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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bureau13  



Joined: 07 Sep 2017
Posts: 67
Location: South Florida

PostPosted: Mon Jan 22, 2018 3:38 pm    Post subject: Reply with quote

It definitely makes sense to check it. Maybe a silly question...but if this were timing would it not be more consistently off? I started it a bit ago and it ran perfectly at idle for about two minutes and then started missing again.
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1534
Location: Somerset, UK

PostPosted: Mon Jan 22, 2018 9:05 pm    Post subject: Reply with quote

Was the engine cold? Was the idle enriched with fuel whilst cold? Once warm did the idle become slower/lumpier once cold enrichment had stopped, circa 2 mins after starting?

Something has changed in the cam belt/cam/dizzy timing. Or you have dislodged something during the work.
_________________
1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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bureau13  



Joined: 07 Sep 2017
Posts: 67
Location: South Florida

PostPosted: Tue Jan 23, 2018 1:17 am    Post subject: Reply with quote

In this particular case, the engine was cold. Cold start enrichment is a possibility, I think. I tried to retest that and get an accurate time, to see if it was consistent, but of course it was no longer cold.

For the belt work itself, neither gear seems to have moved while the belt was off. I placed the belt, with the long crank-to-cam gear side as tight as possible, then tensioned the belt. I was a little concerned that I over-tensioned it but I don't THINK that would cause this in any case.

As I mentioned before, I did move the fuel distributor up and out of the way while wrestling with the cover. I can't see anything visibly kinked, however.

I suppose if I pull the plug wires one by one I should be able to isolate which cylinder is missing.

Carrera RSR wrote:
Was the engine cold? Was the idle enriched with fuel whilst cold? Once warm did the idle become slower/lumpier once cold enrichment had stopped, circa 2 mins after starting?

Something has changed in the cam belt/cam/dizzy timing. Or you have dislodged something during the work.

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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bureau13  



Joined: 07 Sep 2017
Posts: 67
Location: South Florida

PostPosted: Tue Jan 23, 2018 4:49 am    Post subject: Reply with quote

Forgot to mention...I did have the "pipe" that comes from the turbo up and over the valve cover to the throttle body disconnected. I moved it a bit for some extra room. In case that gives any clues about something I may have dislodged...
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1534
Location: Somerset, UK

PostPosted: Tue Jan 23, 2018 8:50 am    Post subject: Reply with quote

bureau13 wrote:
Forgot to mention...I did have the "pipe" that comes from the turbo up and over the valve cover to the throttle body disconnected. I moved it a bit for some extra room. In case that gives any clues about something I may have dislodged...


Vacuum leak?
_________________
1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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bureau13  



Joined: 07 Sep 2017
Posts: 67
Location: South Florida

PostPosted: Wed Jan 24, 2018 1:58 am    Post subject: Reply with quote

Very possible. I didn't take off too many lines, but I could have compromised something. I have a smoke tester so I will give that a go.

When it's missing, I do smell fuel. I can't localize it though, my nose is not directional enough for that I guess...

Carrera RSR wrote:
bureau13 wrote:
Forgot to mention...I did have the "pipe" that comes from the turbo up and over the valve cover to the throttle body disconnected. I moved it a bit for some extra room. In case that gives any clues about something I may have dislodged...


Vacuum leak?

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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bureau13  



Joined: 07 Sep 2017
Posts: 67
Location: South Florida

PostPosted: Sun Jan 28, 2018 7:13 am    Post subject: Reply with quote

Carrera RSR, you nailed it. Vacuum leak...at least, I have one, and I clearly caused it, so I assume that is my problem.

It's that big red o-ring sealing the metal air tube to the throttle body. Pinched it right in half. Smoke test had smoke pouring out of there. It doesn't look like I'll be able to get one locally, so I'll have to order it.

PET shows another seal there, which is NLA. Coincidentally, I found a thread on a different forum from a few years ago where you were looking for this NLA seal and I don't know if you ever found one, but people seemed to think it wasn't critical. My car doesn't seem to have one at all, so apparently it's not.
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1534
Location: Somerset, UK

PostPosted: Sun Jan 28, 2018 10:36 am    Post subject: Reply with quote

Red round O ring is critiical. Black surrounding ring is not. The red O ring can be replaced by any sealing ring of similar diameter and size
_________________
1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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bureau13  



Joined: 07 Sep 2017
Posts: 67
Location: South Florida

PostPosted: Fri Feb 23, 2018 5:56 am    Post subject: Reply with quote

Just to provide closure, replacing the butchered red o-ring did in fact fix the rough running problem. It runs like a champ now, just as before.
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
Back to top
View user's profile Send private message
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