7A cold start and CO% problems

[Azimut]

Hi everyone

Some time ago i bought a 7a engine, rebuild it and installed to my competition.
From the beginning it had problems with MOT, CO level too high.

I tried different things to solve this problem.


At present time i still have problems with CO ~ 0,4% (allowed 0,3% on idle in our country), and bad idle after start in cold weather: starts fine, but after few seconds rpm drops from 1200 to normal idle ~ 800 and start to jump ~600-1100 for about 5-15 seconds and in the end this rpm jumping starting be less and go to normal idle. If start warm engine, this problems dont appear usually. Some times when this problem appear if start to drive and take gear off, rpm will go to idle then drop for second to about 500 and then became normal 800.


What was done:

7A original cataletic converter (before was some noname universal one)
034motorsport injectors
AAH maf (tried 3 different V6 mafs with metal and plastic case )with adjustments by Vag-com
Tried second ECU
Tried few 7a FPRs (now installed modified AAH 4.0bar FPR)
New fuel pump
New coolant temperature sensor (bosch), wiring also controlled to ECU
New knock sensors (new stile with holes for bolts)
Fresh lambda sensor
Checked for vacuum leaks
AAH TPS, idle switch works perfect
Tried 3 different idle valves
New distributor rotor, metal gear also installed
Timing marks controlled, camshafts markes also
NGK iridium plugs with second set of plug wires
Wiring and other staff tested with different manuals, everything seems to be fine


Maybe someone had similar problem ?

found some information on russian audi forum that someone had similar problem but with AAH (2.8 128 kw engine with Hitachi ecu). It was an old thread and nothing about problem solution was found, topic started only discovered that in the moment when this rpm jumping appeared, ignition timing jumped from -15 to 0 and thats all .
Tried to make some video, bad quality and not shore that link will work>

https://vk.com/video65874250_456239019?list=b45d4cf141774163e4

[Azimut]

Vag com dont show any fault code, all measurings according to manual seems to be normal >


Here is a picture from MOT, now lambda measurings are normal, there was a hole in the exhaust system,
CO now is around 0,4 after all what was done this year >

[quattrito]

What I can say you need defo original knock sensors. As 7A seem to act badly with next generation ones. As i have had at least 10+ 7A engined cars and have tried both options.

P.S. Have a lot of 7A parts.

[Azimut]

I have got original knock sensors, they should be in working condition, only problem is to tighten them with 10 N`m. New ones i can tighten with no problem because have suitable tool. If you have experience with both types knock sensors, did you tightened those new ones with 20 N`m as it is written in manuals or 10 N`m as for old styled sensors? Was there a markable difference in engine work with different type sensors. I decided to put new styled sensors after rebuild because read that some 7a owners had done this before and didnt had any problems.

[quattrito]

Tightening didn't affect engines working capability, I tightened them with hand not very hard. Maybe in your situation, it is not the problem of the knock sensors, but my latest engine went mad with those sensors being broken. With new type sensors, engine does work, but seemingly not as effective as with the old ones. I have tested that and some of my friends have told me the same.

[PeterS]

A couple of things to check - look for unmetered air - namely vacuum and other potential leaks after the mass air flow sensor - - check the o ring under the bypass adjust screw in the throttle body - if you disconnect the idle stabilizer the engine should still idle ( it is a damper or shop absorber) - You may need to adjust the idle - see the instructions on www.20v.org. Also check the entire crankcase breather to intake track - the pipe behind the head tends to get gunked up over time.

[M2ki]

HC is also high, and that means unburnt fuel/oil.
Catalytic converter only affects CO.

[Azimut]

vacuum and breather after maf checked few times. O-ring on bypass screw changed and idle adjusted according to 20v.org instructions. I think i should try to put back the original knock sensors.

[Azimut]

HC is also high, and that means unburnt fuel/oil.
Catalytic converter only affects CO.

I know this, but cant solve this problem with too rich mixture. Compression ratios are all good and same in all cylinders, spark plugs are also same color and dry. No oil consumption marked . Thats very interesting. Even when i go to MOT put CO meeter back and start to regulate CO screw on the maf, the measurements on CO move closer to normal, but after some time go back to same as they were before i regulate the CO screw. I also tried this with vag com in the basic settings mode nothing changed.

[PeterS]

It might be time to do a proper compression and leak down test..

[steve briance]

I know you say the CO content is set by the MOT test at 0.3% and yours fails at 0.58 but...that is still quite low in my book. The factory adjusting procedure says to set to 0.5-1.0% and mine ran a LOT better bringing it up from 0.4 - 0.8% (we are allowed 3.5% for old cars)

I find it odd that there is a high HC reading as there isn't actually that much fuel going in by the sounds of it, maybe it is burning oil? Did your rebuild include new piston rings?

I also remember seeing on here people having issues with spark plugs and i notice you have NGK Iridium. I tried those once on the promise of having a longer service life. didn't notice and difference to be honest and i know some folk on here have trouble until they go back to triple electrodes. Although i think the cause of your trouble is fuel metering, do you have a set of triple electrode NGK to try?

What is modified about the FPR?

Have you tested fuel pressure in the rail?

[Azimut]

I know you say the CO content is set by the MOT test at 0.3% and yours fails at 0.58 but...that is still quite low in my book. The factory adjusting procedure says to set to 0.5-1.0% and mine ran a LOT better bringing it up from 0.4 - 0.8% (we are allowed 3.5% for old cars)

I find it odd that there is a high HC reading as there isn't actually that much fuel going in by the sounds of it, maybe it is burning oil? Did your rebuild include new piston rings?

I also remember seeing on here people having issues with spark plugs and i notice you have NGK Iridium. I tried those once on the promise of having a longer service life. didn't notice and difference to be honest and i know some folk on here have trouble until they go back to triple electrodes. Although i think the cause of your trouble is fuel metering, do you have a set of triple electrode NGK to try?

What is modified about the FPR?

Have you tested fuel pressure in the rail?

Ive forgot to mention that now is installed normal 3electrode plugs, ive tried 2 different 7a FPRs, one was bad, now i made a case for FPR like AAN has and installed AAH FPR 4.0bar, also controlled pressure in rail with gauge ,vacuum control works from throtle body also. Rebuild was done with new piston rings ofcourse, after 5000km Ive measerured compression and its good and same in all cylinders. Engine do not burn oil, no smoke, plugs are good, and i dont add oil from change to change.

[Bowie69]

Am interested here, in the cold I get these symptoms also... completely standard 7A but with earlier banana manifold.

Have tried multiple ISVs, FPRs, ECUs, different plugs, new leads, coil, rotor and cap, disconnected engine breather entirely, disconnected carbon canister, compression is around 170PSI when cold, no faults shown through OBDeleven.

[steve briance]

did you try the fuel flow test?

It seems to be the only thing you haven't done!

Somewhere on the web is a figure of 800ml coming out of the fuel flexible hose where it goes to the fuel rail in 15 seconds with the pump activated.

Just for the record, i have exactly the same problem (is there a 7A which doesn't do it) and checked my flow rate and it was fine but it is easy to do and nice to know it is not the problem.

I've been thinking recently that it might be something to do with damp. My coolant temp gauge and fuel tank gauge are less intermittent in the warmer weather than the middle of winter and i think my idle problems also get better with warmth but that could just be that the engine is warm of course!

Over on another forum someone transplanted a 7A into an old VW passat estate and remember him having problems with the ISV and tracing that to be a bad wire from the ECU. He said it had very high resistance such that the ISV wasn't getting enough energy to react quickly enough. This sounds familiar to me as when i drive and dip the clutch coming to an idle in neutral, if i dip the clutch at 1500-1600rpm, no problem. If i dip clutch at 1000-1100 rpm = quite often a bouncing idle 200-800rpm before settling. My ISV is clean as it has been in an ultrasonic tank but i do wonder if the signal from ISV pin on ECU is not getting through and the ISV needs a bit more time to work...

One day i may run a test wire rather than undoing the loom.

[steve briance]

hmmm.

Where are you measuring the CO from?

On the tubular manifold there is a CO measuring point PRE CAT. MOT people never use it but i wonder if setting the correct reading there would = an MOT friendly reading at the back?