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Hesitation/Missing
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Sat Mar 13, 2021 5:38 pm    Post subject: Hesitation/Missing Reply with quote

Oy, this is starting to get a little tiring.

I rebuilt the throttle Body, and that did nothing.

Now after my last test drive, It all of a sudden started hesitating from a stop, but seemed better after I got moving.

So i rebuilt the TB, put it all back together and No improvement.

Right now its definitely missing at idle and the AFRs are bouncing.
I can't figure out what the issue is yet.
I tried Spraying all the hoses/gasket areas with Starting fluid, and it made no difference, I couldn't find any area with a leak (yet) (where as I did before with the TB and the crack in the injector spacer)

I was thinking it might be the Intake gaskets, but the last time I had the intake off(several years ago, but I've only put maybe 100mi on the car since) I threw some RTV on them (didnt put new ones on) But youd think the starting fluid would have found a leak)

I've replaced all the Vacuum lines and most other hoses, and half the rubber elbow (again the Starting fluid test didnt find anything in those areas)
No coolant in the oil and no oil in the coolant. No smoking out the exhaust.

Holding the throttle open it seems smoother But I still hear an occasional miss and the AFRs bouncing.

Im hoping I havent burnt a piston or valve.

Sigh....
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Sat Mar 13, 2021 5:49 pm    Post subject: Reply with quote

Oh Also checked for loose spark plugs
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2194
Location: Somerset, UK

PostPosted: Sat Mar 13, 2021 6:10 pm    Post subject: Reply with quote

Why create this new thread? Same problems and suggestions as per your ongoing AFR thread. Starting a new thread in a new location isn’t going to change advice or find a new solution. Get it on the dyno with an experienced Kjet technician.
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Sat Mar 13, 2021 6:51 pm    Post subject: Reply with quote

I didn't think it was the same problem, was starting to dial in the AFR. (I think the TB seals would have helped, If I was able to drive it again)
This just popped up, wasn't having this issue previously.
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Carrera RSR  



Joined: 08 Jan 2010
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Location: Somerset, UK

PostPosted: Sat Mar 13, 2021 10:40 pm    Post subject: Reply with quote

MikeDanger wrote:
I didn't think it was the same problem, was starting to dial in the AFR. (I think the TB seals would have helped, If I was able to drive it again)
This just popped up, wasn't having this issue previously.


You just dialled in you AFR with a vacuum leak. Now you fixed the leak you need to dial it all in again without the leak. Welcome to the CIS juggling act. Every action has a reaction....... you fixed the leak, now fix the idle fuel and air mixture and then the AFR if that changed.
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924RACR  



Joined: 29 Jul 2001
Posts: 8420
Location: Royal Oak, MI, USA

PostPosted: Sat Mar 13, 2021 11:07 pm    Post subject: Reply with quote

Speaking of why i finally ditched CIS for MS...

Though admittedly, I didn't completely purge the missing from my 931 until post-MS conversion, when I ditched the stock dizzy and ignition and went to the VW 4-tower coil.

Not to discount all the issues with the CIS, Mike I forget what kind of ignition setup you're using - still stock or did you already purge that?
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Sun Mar 14, 2021 2:14 am    Post subject: Reply with quote

Carrera RSR wrote:
MikeDanger wrote:
I didn't think it was the same problem, was starting to dial in the AFR. (I think the TB seals would have helped, If I was able to drive it again)
This just popped up, wasn't having this issue previously.


You just dialled in you AFR with a vacuum leak. Now you fixed the leak you need to dial it all in again without the leak. Welcome to the CIS juggling act. Every action has a reaction....... you fixed the leak, now fix the idle fuel and air mixture and then the AFR if that changed.


Im pretty sure this is a "new" problem. It wasn't missing like this before and the AFR was more steady. The lack of power on takeoff happened suddenly. (it was running pretty well and felt like I was 90% there with the AFR's) If the TB was the issue, then it should have been better after replacing those seals. Adjusting the Mixture made no difference in the Missing.


It SEEMS like a Bigger Vac leak than anything before.... but if it was that big, how come I can't find it with the Starting fluid/ether? Which now makes me worry its something more serious?

Can I rule out Piston/Rings/Valves/Head gasket?

My initial lean was towards the Intake gaskets, but the Starting fluid test isn't making a change (well I thought maybe I possibly heard a slight change when spraying near the back of the intake, but it might have just been the engine fluctuating due to the problem, because it was such a minor change, rather than an "ah-HA, I found it!" type of change.)
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Last edited by MikeDanger on Sun Mar 14, 2021 2:29 am; edited 1 time in total
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Sun Mar 14, 2021 2:22 am    Post subject: Reply with quote

924RACR wrote:
Speaking of why i finally ditched CIS for MS...

Though admittedly, I didn't completely purge the missing from my 931 until post-MS conversion, when I ditched the stock dizzy and ignition and went to the VW 4-tower coil.

Not to discount all the issues with the CIS, Mike I forget what kind of ignition setup you're using - still stock or did you already purge that?


All stock for now, (Learned my lesson on the 2 previous 931, Don't take it apart before you're ready to put it back together!)
this is an 81 So I figured it should be more reliable than the S1 (of course until the crank sensor fails!)

Ive replaced the Cap and Plugs, and someone in the past replaced the Wires.

Just a bummer being so close to being driveable, and then adding the FMIC.
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TJC  



Joined: 04 Apr 2010
Posts: 808
Location: Central-ish Arizona, USA

PostPosted: Sun Mar 14, 2021 2:34 am    Post subject: Reply with quote

[quote="MikeDanger"][quote="Carrera RSR"]
MikeDanger wrote:


Can I rule out Piston/Rings/Valves/Head gasket?



Perform a comprehensive compression test and cylinder leak down test to answer this question.
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2222
Location: MI

PostPosted: Sun Mar 14, 2021 2:53 am    Post subject: Reply with quote

[quote="TJC"][quote="MikeDanger"]
Carrera RSR wrote:
MikeDanger wrote:


Can I rule out Piston/Rings/Valves/Head gasket?



Perform a comprehensive compression test and cylinder leak down test to answer this question.


That..

And you should/should have probably added the IC before tuning, to keep it from exploding on a poor tune..
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2194
Location: Somerset, UK

PostPosted: Sun Mar 14, 2021 3:29 am    Post subject: Reply with quote

YES! It will be a new problem. You previously dialled in the Idle fuel and air mixture plus AFR with potentially an air leak in the throttle body. Now you fixed the air leak in the throttle body YOU MUST reset the idle fuel and air mixture. Your job starts all over again........
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Sun Mar 14, 2021 9:19 am    Post subject: Reply with quote

Carrera RSR wrote:
YES! It will be a new problem. You previously dialled in the Idle fuel and air mixture plus AFR with potentially an air leak in the throttle body. Now you fixed the air leak in the throttle body YOU MUST reset the idle fuel and air mixture. Your job starts all over again........


yes but IF the TB was the issue there should have been some improvement, that leak was minor at best. I'm sure it was probably leaking before, and it wasnt missing like it is now.
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Sun Mar 14, 2021 9:28 am    Post subject: Reply with quote

So I have a new Clue.
I just started it (cold engine) and didn't get the missing...for the first 3-4 minutes, I thought "hey, it's gone?" and the AFRs were steady and climbing to around 14.5

Then it started again. AFRs bouncing between 13.7 to 17 quickly.

I tired to use a propane torch to look for leaks but found none. Again adjusting the mixture made no difference in the missing.

What would change in those first few minutes? Something heating up? a crack getting bigger?
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MikeDanger  



Joined: 21 Nov 2002
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PostPosted: Sun Mar 14, 2021 10:41 am    Post subject: Reply with quote

is there any way to disconnect the o2 from the top of the engine/cockpit?
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Mike9311  



Joined: 14 Dec 2004
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PostPosted: Mon Mar 15, 2021 1:58 am    Post subject: Reply with quote

I've read most of what you've posted but I don't think I have seen you check your plugs?

Run the car with the miss and turn it off. Then check your plugs. Do they all look the same or is any single one different?

I always start at the plugs because they tell a story and it really is the easiest thing to do unless you are tmic'd of course
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