Boost problems

Ameer Antar ameer at snet.net
Thu Oct 5 14:20:47 EDT 2000


so how do you know what yer mixture is. A great diagnostic tool is a 
air-fuel ratio gauge. It will tell you everything about the fuel system. 
That's not true about leaks causing rich running. That's only true above 
1.0 bar. Air will be sucked in to the engine thru the leak which was not 
measured by air flow sensor. Beyond 1.0 bar, there is more pressure in the 
intake system, so rather than outisde or false air entering the engine, it 
actually is escaping into the lower pressure atmosphere. Most people run 
under 1.0 bar, so as long as you're not under boost, leaks before or after 
the turbo cause lean running. Above 1.0 bar leaks after the turbo causes a 
slight rich mixture and low boost pressure. Above 1.0 and before the turbo, 
it will again cause lean running. If you had a gauge to look at, you'd know 
exactly what was going on. There are many places for leaks to occur on Audi 
turbos. The only way to know a hose is not leaking is to remove it. Leaks 
can be real hard to spot w/ a flashlight in some awkward angle. Also cracks 
many times occur right where the clamps are, making it even harder to spot. 
Check the whole system.

The hard starts, is prolly a bunch of things combined w/ a leak. If yer 
injectors are older than 60k, change em. It's real easy to do, esp. on the 
early 5kT's cuz there is no inj. insert. The best way to diagnose a CIS 
system is w/ a fuel presssure gauge, but 95% chance yer warm-up regulator 
is dead. Check the resistance of it. It should be 17-21 ohms. The real way 
to check the reg. is to watch the control pressure rise to about double the 
cold value. Mine was 55psi the whole time, cold or hot, so the reg. was 
telling the engine it was always warm, leaning the mixture. Probably what 
happened was the control valve inside seized or broke it's connection w/ 
the bimetal coil. There maybe other issues, but hopefully yer plugs, wires, 
filters, etc. are in good shape...

good luck.
-ameer


At 12:29 PM 10/5/00, you wrote:


>Heya,
>
>    Thanks for the post.   Sorry for the late reply.    I've exhausted 
> possibilities of a vaccum leak.  Its well sealed.   Checked under 
> pressure.   BTW though, on a turbo engine the mixture goes rich with a 
> vacuum leak as it bleeds off air and still injects fuel.  But it could be 
> before the turbo, I haven't checked there much.  I should.
>
>    As for injectors, definately a possiblilty but not my only 
> problem.  Probably why its hard starting in mornings but not the fix for 
> my lean running.    I fixed the lean ness on boost by disconnecting the 
> Warm up Reg heater. This means the Warm up Reg is at engine temp an not 
> more.  This seems to make it great once warmed up but its slow to warm 
> up.   I wonder if my warm up reg heater element was just over 
> active?    Or possibly fuel pump flow isn't high enough.
>
>    Anyhow, thanks for the help.   Its always nice getting another opinion.
>
>l8r
>
>   Todd
>
>   Ameer Antar <ameer at snet.net> wrote:
>>There are a lot of possibilities here. First check your engine mounts. They
>>don't usually go bad very quickly, but are vulnerable to oil and heat on
>>the turbo side. When the engine is above 1 bar, it may vibrate a little due
>>to the pressures and more if there is any internal imbalance. This
>>imbalance could be mechanical or caused by one injector leaking or other
>>engine control problem. Check the ECU pressure line for leaks. Also a small
>>vac. leak in the intake can cause a lean mixture at high throttle and
>>normal mix at low throttle. The vibration may be caused by lean running.
>>Are you getting full boost? If so your leak will not be in the intake
>>system between the turbo and throttle body. Any leaks in this area will
>>reduce full boost. Leaks from the air-flow sensor to the turbo will cause
>>lean mixtures. The hard starting hot or cold points to injectors. If you
>>haven't changed these in 80k miles or so, you should. I found the best and
>>easiest diagnostic tool is an Air-fuel ratio gauge. You can get a cheap one
>>for $25 or so from JC Whitney or a nice autogauge for $50. All you do is
>>crimp a 3-way splice onto the O2 sensor lead and connect 12V to the gauge.
>>It will tell you everything about mixture conditions, under boost, accel,
>>decel, whatever. It also shows when the ECU is controlling the mixture when
>>you see the mixture cycle on and off. Once you figure out if it is a fuel
>>issue, you can decide what to replace instead of having to guess. good luck
>>and let us know what you find.
>>
>>
>>
>>At 12:31 PM 9/25/00, you wrote:
>> >While driving the '91 200q (all-stock) around town this weekend, I noticed
>> >the following problem:
>> >
>> >When I "get on it" and the engine develops boost above 1.2 bar, the engine
>> >(and entire car) bucks like a bronco(!). It can be quite disturbing if
>> >you don't expect it. And it's tough dri ving the car and intentionally
>> >accelerating *slowly* :)
>> >
>> >I'd suspect vacuum (or actually pressure) leaks somewhere. I'd think when
>> >the engine is running vacuum (<1.0 bar) it doesn't care if it sucks air in
>> >from the leak or from the airbox. Once the turbo pressurizes the system,
>> >the air gets pushed out of the leak because it's under positive pressure.
>> >
>> >Could this also be related to another problem I've been having
>> >recently? The car is hard to start. It will take a considerable amount
>> >of cranking for it to initially "catch". Once it does, it idles
>> >fine. Does not seem to matter if the engine is cold or hot. FWIW, once
>> >started, the exhaust smells as if it's running rich.
>> >
>> >Any possible causes, or more importantly - solutions?
>> >
>> >State inspection is due at the end of this month. I'm sure my mechanic
>> >would love to charge me for some work... I'd like to "cut him off at the
>> >pass".
>> >
>> >(Another reason to own a quattro - they can't put the car on the NYS dyno
>> >inspection machine because of the AWD. They can only use the sniffer in
>> >the tailpipe.)
>> >
>> >-RJM-
>>
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>
>
>Todd Phenneger
>83' ur-q (awaiting a 20vt)
>84' 4ktq fun but I'm sick of CIS.
>
>
>
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