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Matt
Matt, Engineer
Category: Audi
Satisfied Customers: 17283
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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audi 90 sport: I have a 1994 Audi 90 sport. Its been having

Resolved Question:

I have a 1994 Audi 90 sport. Its been having trouble running smooth in the morning when it was either cold or especially when it was wet. I assumed this was due to the spark plugs or wires. So I bought the plugs first since they're cheaper and hoped that was all that was needed. But before I had a chance to change them, my dad decided to mess with it and I think he may have reconnected the wires wrong. I went to start it this morning and there was a lot of popping almost like backfiring. So I changed all of the plugs hoping that he just messed one of them up somehow. After changing the 4th plug and attempting to start the car, it just turns over while the key is turned but dies as soon as I stop turning the key. I changed the last two plugs, but still nothing. So my questions are 1. Where can I find the wiring order for the spark plugs and 2. If that isn't the problem, then what is?
Submitted: 1 year ago.
Category: Audi
Expert:  Matt replied 1 year ago.
Hello

can you tell me what engine this is please? the 4 cylinder , v6 , engine size?
Customer: replied 1 year ago.


its the v6 but I don't know the size exactly

Expert:  Matt replied 1 year ago.
OK thats enough

this diagram should help - firing order is at the top

graphic
Customer: replied 1 year ago.


right I knew that because its written right on the end where the wires connect. But how do I know that the wires are in the right order?

Expert:  Matt replied 1 year ago.
Hello

the order of the leads onto the coil packs shodul be looking at the engine from the front on the left hand side of the coils the leads go 1,2,3

1 being the nearest to you
And on the other side it go's 6,4.5
6 being the one nearest to the bulkhead

it should also be marked up on the coil pack with a sticker as to what lead goes where
Customer: replied 1 year ago.


then that's not the problem... They're all in order. Any other ideas?

Expert:  Matt replied 1 year ago.

Hello

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth cleaning out the idle speed control motor / valve as these get clogged up with carbon and some brake cleaner washed through helps free things off.

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.

This leads them to be quite intermittent in the case of mild leaks

its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue

On no account touch the sensor wires with anything physical as they are extremely fragile

Matt, Engineer
Category: Audi
Satisfied Customers: 17283
Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Matt
Matt
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Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing