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Discussion Starter · #1 · (Edited)
Can anyone else, who has a AFM on their C20LET, tell me what they see on their 2L 16V C20LET engine at idle (cold).

My engine used to run fine and for the past few months its not idling good when cold (ie first thing in the morning), it can struggle and then stall. I've never noticed my Air/Fuel meter (AFM) till now - it reads lean. If I keep the revs up (ie 2K-3K) for about 30sec then it idles fine (but still shows lean).



Using opel-scanner shows when the CTS reads +60ºC or greater then it operates in closed-loop mode and the engine idle's spot on. The ECU, when cold, should run rich at idle until the engine has got up to temperature - buts its not and I'm trying to figure out why.

So I want to know what other people see on their C20LET at idle (when cold).

Engine spec:
Rebuilt 10 years ago by myself and idled fine until a few months ago. Full engine rebuild with K16 running Phase2. Uprated fuel pump, Saab Reds, adjustable FPR (measures 3bar with vac hose off).
Had a puff of smoke at first start and lumpy idle/stalls at idle. Engine compression check shows 200psi on all 4 pots. Spark plugs all look dry and good colour. Diagnosed this down to possible leaky oil stem seals (ie oil dripping into chamber over night and at first start burns it off - hence the smoke). All replaced last week and included C20XE inlet cam mod with vernier pulley wheel. Puff of smoke on first start now gone (good) but still struggles to idle (bad). Also in these past few months I get error code 113 (boost out of range) - is this related?

== SOLVED ==
So basically problem fixed.
Fault was down to:
  • vacuum leaks
  • incorrectly set vernier on c20xe inlet camshaft mod

The ECU error code 113 was due to the large air leak in the inter cooler. ECU measured air though the Airmass meter but due to the difference in boost it thought it would be producing and the actual result it was measuring (at the boost sensor in the ECU), due to the large mis-match i flagged up error code 113.
 

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I have a wideband on my cav turbo, at cold idle it runs in the 12s and 13s, running rich, when it warms up it starts to lean out and settles at 14.7 or there abouts which is normal stoich. Ads
 

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Discussion Starter · #4 ·
So everyone (so far) is running rich at idle when cold. So the problem with mine sounds like its running lean at idle when cold......just got to figure out why.
I've checked the fuel pressure, get 3bar with vac hose off.
IT could be poor fuel spray pattern on the fuel injectors, but then again, when the engine is in closed-loop mode the idle is spot on and never misses a beat (suggesting the fuel and pressure are ok).
Closed-loop mode kicks in when the CTS = 60deg or higher. CTS seems to be reading sensible figures from cold to hot - so I'm happy its not the CTS.
 

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Discussion Starter · #6 ·
is it worth changing the cts we all know the problems they can cause ,,, and autovaux have geniune bosch ones in stock
Got a genuine Bosch item already fitted. In fact I do have another spare (used).
Anyway, using the scope plot function on opel-scanner I can see the CTS (and hence its wiring) are all working fine. The reading is linear from cold (about 18ºC at the time) to well past closed-loop stage (>+60ºC) and at +70ºC my engine dash water gauge started reading and was matching/tracking the CTS, so it all looks fine.

I've been doing data captures using the opel-scanner. But its a slow process because I can only do it once a day, early in the morning when the engine is cold...and for only about 30-60 seconds because after that the engine runs better (doesn't stall but still lumpy until it reaches closed-loop mode).

What I want is another C20LET owner close to North Kent where I can plug in the opel-scanner and make comparison with my car at idle when cold.
At the moment I have loads of data but I don't know if its right or wrong.
 

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Just had a re-check of mine and even when cold its trying to keep 14.7 but with fast idle as you would expect.

Mart
 

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Mine reads between 15.2 and 16 when cold, I wait about 1 minute before I drive off, this helps, but sometimes I still see high 15's when cruising, till it warms up properly.
 

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Discussion Starter · #10 ·
An update on why my engine is running lean and cutting out on idle.
Connected up the opel-scanner and read a lot of live data and did the actuator tests. All seems ok, AFM readings all ok, TPS readings all ok, CTS readings all ok, ISCV readings all OK, fuel injector pulses all OK. The only thing is that the engine hunts on 1st start and can't keep the revs up and stalls. So I don't think its an electronic sensor fault.





 

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Discussion Starter · #12 · (Edited)
As I don't think its an electronic sensor or actuator problem, its back to basics.
I did a compression check, all 200psi, no problems there.

Next I checked the spark plugs, again they all look ok, correct colour, dry, no cracks on the ceramic body, tip looks good and gapped correctly.


Next was the fuelling, with vac hose off I read 3bar which is correct (uprated fuel pump and Saab reds. Been set up the rollers at the beginning of the year and got 10-12 at WoT at 3Bar)


I also checked the condition of the OS as these can block up over time. Again this looked in good condition and was dry (so turbo or engine is not leaking seals).


so no problems found so far.
 

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Discussion Starter · #13 ·
Whilst looking at the condition of the pipes for air leaks etc I noticed that the MAP/boost pipe from the engine bay to the ECU had a T-piece on it for my Boost gauge connection. However it the diameter of the pipes were wrong so to thicken up the T-piece half electrical tape was used! I can't remember doing this but it must of been me as I'm the only one that works on it. Took the pipes off and gave everything a good clean and blow out and refitted with better fitting rubber pipes. Tired the car again but still stalls on 1st start with cold engine. so this was not the problem.

 

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Discussion Starter · #14 ·
Still checking for air leaks as I'm sure that's the problem. I think metered air is escaping, so the ECU thinks X amount of air is entering the engine and injecting fuel in buts its the wrong mixture. Too little air and it will stall, so it tries to increase the revs with the ISCV but it still an't do it (too much air escaping) and it stalls. With this much air escaping I though I would be able to hear it but it all sounds good.

To find vacuum/air leaks I tried a few methods:
  1. Soapy water with engine running. If there is a vacuum leak you hear it get sucked in and engine revs dip a bit. Very safe to use.
  2. Spray Carb clean or WD40. Does the same as above but more effective. The downside is that on a hot engine is can be dangerous (ie flammable liquid).
  3. Smoke test. Proper automotive tool is expensive (£1000) and garages can charge £50/hr for using one. So I bought a party smoke/fog machine from Maplin with water based fog liquid, some old rubber piping to make the connection up and it worked like a charm.



It found 2 leaks
1 was on the hose to top-hat connection. My large wider claps were too wide so they were clamping down on the lip to the top-hat, thus not actually making a air tight clamp. so had to go back and use a thinner jubilee instead. Job done.
2nd one was harder to find. I could see smoke coming around the bottom of the rad in the engine bay. Jacked the car up and it was coming out the intercooler area which lives in front of the rad. Took the front bumper off and smoke was coming out from a weld seam on the intercooler. There was a hair line crack along the whole seam. I would have never found that! Plus that would also be a large boost leak too (this may explain error code 113 - boost out of range).



I managed to find a local engineer shop that would weld aluminium and got it fixed for £40.
Put the whole car back together and repeated the same tests above. No air leaks.
 

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Discussion Starter · #15 ·
With all vacuum air leaks found, no problems with engine sensors or actuators, and all the basics looking good I started the engine up cold and.....it worked! It didn't stall.
Tried this over a a week or two and each cold morning the engine fired up 1st time, didn't stall and idled good. The only convern was that I noticed that the vacuum readgins were reading low and the fueling looked lean still.
Some of this was answered in this post.
http://www.migweb.co.uk/forums/engines-transmission/685713-c20let-xe-cam-mod-map-vacuum-readings.html





Basically the vacuum reading was due to a misleading gauge and fuelling was due to an incorrectly set c20xe inlet camshaft mod.

So basically problem fixed.
Fault was down to:
  • vacuum leaks
  • incorrectly set vernier on c20xe inlet camshaft mod
 

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Good to see all that perseverance was rewarded and thanks for posting it - may help some other poor soul with the same problem.
 

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Excellent diagnostics, glad you sorted it, I've got an Autogauge Vacuum/Boost gauge, but the one that goes black when ignition is off.
 

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Nice find there. :D
I have a very similar issue with my LET, but mine idles like crap from cold for about 6 minutes, then switches to running perfectly. I've changed the CTS and ICV with no joy.
No EML either.
I'll start tracking down vac leaks this weekend.


Is that a genuine OpelScannerCAN?

I've got a hookey OpelScanner Advanced and it can be a but unreliable when the engine is running (disconnects), but apparently, the ECU is a bit noisy and comms can be a bit hit-and-miss. Seems to be fine with other cars though.
 
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