Meny

Hello everyone.
I wanted to share my experience diagnosing and repairing a hard start problem in my 2001 A6 2.8 (I apologize for my bad english in advance, as I am from Juarez, Mexico).
I imported the car to Mexico from the US several years ago and never had any major issues with the car before.

Symptoms:

The car had trouble to start the engine when it's been off for more than 15 minutes.
If I just turned off the engine, it will start immediately and remain running for as long as needed without problems.
If the engine is off for 15 minutes or more, I have to crank it for 15 to 20 seconds for it to start.
It makes no difference if I press the gas pedal, it will start from 15 to 20 seconds max.
The engine always starts but it's annoying to have to crank for so long, I feel I can damage the starter.

Backround:

I have moderate mechanic skills as I have some experience with auto repairs and modifying/tunning. I also own a good set of tools and a Injectronic CJ4 diagnose tool (No VAG tool/cable yet).
I work for a major international IT company as a service request project manager, so I can work from home all the time if needed, therefore, I have time available to set up a mini auto repair/garage at home whenever I need to (Repair engines, heads, change timing belts, water pumps, brake jobs, tune ups, etc).

Repair:

I started by checking with a diagnose tool. No codes and no check engine light on
Did a data stream check with my CJ4 tool and saw that the coolant temperature was high, even when the engine hasn't been on for several hours.
So I did the logical thing and replaced the green coolant temperature sensor hoping that this would fix the issue.
No luck, the problem remains the same. The car needs about 15 to 20 seconds of cranking to start

So now I need to check the fuel pressure, maybe the problem is with the pump. Since I have a universal fuel pressure testing kit, I didn't had the correct fittings for this Audi.
I went to the back of the car in the passenger side, were the fuel filter is located and saw the fuel hose that goes from the pump to the filter, so I removed the hose from the filter inlet and installed a T fitting, this allowed me to connect my pressure tester.

Started the engine after about 20 seconds of cranking the starter.
I figured that since the pressure was released and the fuel drained from me removing the fuel hose, it would take even longer to start the engine. But no, It took about the same time to start it.
So now I am certain that the problem is fuel related.
The fuel pressure is 50 psi when running, so pump is delivering the needed pressure.
I disconnected the vacuum hose from the fuel pressure regulator and it went up to 57 psi. All good and since the pressure regulator is not leaking fuel, I discarded the fuel pressure regulator.

So now I focused on the residual pressure, as per Alldata information, the residual pressure needs to be about 2 bar (30psi approx) after 10 - 15 minutes of turning off the engine. Mine went to 0 after just 10 minutes.
By then I knew the car is loosing fuel pressure after I shut down the engine, and when I need to start it again, it has to build up fuel pressure from 0 psi and this takes about 15 to 20 seconds to start the car.

I my mind only 2 things can cause the residual pressure to drop to 0:
1. Fuel leak
2. Bad fuel pump (Check valve).

So I visually inspected for leaks. None
I removed the fuel rail with the injectors still attached to se if one or more are leaking while engine off. None

This only leaves me with the fuel pump, since the Audi parts are almost unavailable here in Mexico, I really hoped that I didn't had to replace the pump because of the price and hassle to get it.

I figured that since the engine runs great and the problem is only at start up, the pump is not the problem.
The issue is with the check valve that is not working and the residual fuel pressure goes back to the tank.
How do I replace/repair the check valve with out replacing the entire fuel pump?

The check valve is integrated in the fuel pump assembly, so what if I just install an aftermarket check valve as closes to the pump as possible to retain the residual fuel pressure once I shut down the engine......

Yes, this is possible. So I took a look in the internets and found that this is a problem with a lot of cars from all makes.

I found several fuel check valves available. eBay and Amazon but all seem low quality and not suitable for fuel injected cars, only low pressure carburated ones.

I found one in a DeLorean forum, for fuel injected systems that will work on my Audi:

SMC 410 Check Valve, 5/16", high-pressure

410 Brass Check Valve 5/16"HB x 5/16"HB w/Viton® - 1 PSI Cracking Pressure | U.S. Plastic Corp.

I order one and arrived in 2 weeks, installed it in 10 minutes and now the problem is gone.
The car starts immediately no matter how long the engine is being off.

wohooooo, $ 20 dlls fixed the problem and I kept my OEM fuel pump.

I hope this helps someone that has the same hardstart problem I had with my Audi.

Sorry for the long post, and since I don't have a potato pic, please imagine one with the Audi rings in the middle.

Thank you.

johnkk

Well done diagnoses and fix. Your write-up is probably clearer than most whose first language is English!

Interesting that Audi parts are hard to find in Mexico, since VW's are made there.

georgeb944

My sentiments exactly! You clearly have a knack for diagnosing problems!

Welcome to the world of Audi!

jcman

It's always refreshing to see an extremely well thought out and presented thread to help out the members, you nailed it with the bullet points....Bravo!

Meny

Yup, VW Jettas, Rabbit/Golf and Beatles are made in Mexico, but Audis and Passats not, so parts are rare, good thing I can go to El Paso, TX to buy parts.

Thanks