Car will not start

4.2 V8 32v Naturally Aspirated - 414 bhp
willu17
Neutral
Posts: 21
Joined: Mon Feb 08, 2016 11:01 pm

Re: Car will not start

Post by willu17 » Sun Mar 31, 2024 6:03 pm

willu17 wrote:
Sun Mar 31, 2024 6:02 pm
I’ve been plagued with issues. New battery, new starter, new clutch switches. Each time I replaced one I thought I had fixed the issue, but after a week or so it would come back until finally the car was stranded and wouldn’t start at all.

I managed to diagnose a dodgy earth strap by putting a jump lead between the earth rod under the battery scuttle and the engine block. The car started straight away.

To fix this I have put a new earth strap between the chassis and engine block and I’ve had no problems since..

KNN
Neutral
Posts: 5
Joined: Thu Feb 09, 2023 6:53 pm

Re: Car will not start

Post by KNN » Fri Apr 05, 2024 9:02 pm

Hi,

I had this issue since day one of my ownership, previous owner wasn't sure so his workshop. One thing to take note, the start is instant during a cold start but after few runs and stops, I had difficulty starting, had to try at least 10 to 15 times of this cycle (switch off, switch on, clutch in, brake pedal and press start)!

It was embarrassing not being able to start when everyone is in and ready to move, especially when it is hot outside, never been cold here with tropical weather. There is only about 15 to 20 in this country, so my mechanic did not get a chance to work on this issue.

Long story short, I went through all those things which could prevent these cars from starting, decided to try spending few months to eliminate the root causes one by one, on my own before resulting to change the starter. Scan the car completely and save the results, clear the codes. Between each step outlined below, I gave myself some time to see if the intermittent starting has reduced or no impact.

1. Changed to the right battery - Previously it was a battery called AMARON DIN 110, however Audi told me that based on their scan some modules were not getting enough power. They recommended me to change to VARTA specific model code, but I changed them outside the dealership. Step 1 done.

2. Replaced upper Clutch Pedal Switch - step 2 done

3. Replaced lower Clutch Pedal Switch - Even though this was replaced, I believe there was a rubber on the small metal plate which was supposed to push the switch completely. This was missing, so I found a square black rubber, cut them nicely and fitted onto the lower pedal metal piece. - step 3 done.

4. Replaced brake pedal Switch - It may or may have not interfered with starting process, but usually we will have to press the clutch and the brake pedal before starting, so I replaced them. step 4 done.

5. Replaced Starter Relay 1
6. Replaced Starter Relay 2

These starter relays, can become faulty over time and may not work well when it is warm. There are 2 of them, so please replace both. Why do I say it will become warm/hot, because when I was doing this experiment, I removed the lower trim below the steering column so that I can easily switch the old and new ones for testing. One thing I noticed was, without the lower trim which had some thick padding, you can feel the warmness on your right knee which was close to the area with fuses/relays. To clear my doubt I bought a industrial grade Bosch temperature sensor and pointed at the fuse/relay black boxes in that area and believe me it was almost 50'c plus, after some driving.

After replacing all of the above, the chances of starting after driving became better. Then I realized something, usually when we switch on the ignition we could hear the fuel pump making a sound briefly but this wasn't happening before each start. So I would usually press the gas pedal briefly before pressing the start button, and I can hear the fuel pump going off. So I decided to change fuel pump relay, there are two in the fuse/relay box at plenum chamber. These relays have been updated with new colour and new 3 digit numbers on them, probably revised version.

7. Replaced Fuel Pump Relay 1
8. Replaced Fuel Pump Relay 2

I now can hear the fuel pump priming when I turn on the ignition. Situation improved, much better than before but still not satisfied..

9. Finally, the last thing was the starter which I doubt would fail that easily. Looked at the ground cable between starter and body, it was not in the best condition, so added another thick custom ground cable onto the existing original cable.

Now, in the morning car starts without any issue, even after driving it starts as usual. There were one or two instances it did not start in the first attempt, but started within 2 or 3 attempts, however this is now very very rare, maybe 1 out 20 to 30 starting procedure. If it goes south again, then I need to start looking for a brand new starter hopefully not anytime soon.

I hope you do not have to go through all of the above, but worth the attempt. Good luck!

GhiniRS4
Neutral
Posts: 28
Joined: Tue Dec 12, 2017 12:57 pm

Re: Car will not start

Post by GhiniRS4 » Thu Apr 11, 2024 9:31 am

Hello,

Recently, I replaced the starter motor. Previously, I had replaced the starter relay and battery for this issue, but after every 3-4 days, the vehicle still couldn't start smoothly, and the problem persisted.

This time, I handed it over to a professional technician for handling. Initially, the technician noticed this issue. He tested it by holding down the start switch button for 15 seconds before it could start smoothly. This situation seems like it needs to be preheated before starting?!

After removing the starter motor and comparing it with the new one, as shown in the figure below:
2024-04-11 162531.jpg

At the joint circled in red, the aging of the joint increased the resistance. The technician believed it resembled a preheating process. It seems like a resistor problem where the voltage couldn't reach the required power supply, resulting in a failure to start smoothly. There might be a problem with the starter motor or the power supply circuit to the starter motor, including the possibility of internal coil aging, etc. In any case, some components, due to long-term use, cannot operate normally, the resistance increases, and finally, it requires a process similar to preheating the circuit before activating the power supply to trigger the starter motor to operate.

Although the removed starter motor was not disassembled for inspection, the current testing after 7 days showed satisfactory starting conditions. It started smoothly with a single press of the starter motor button.

The above information is provided based on my personal vehicle condition for sharing experiences. There may also be other reasons. Each person's vehicle condition may vary. It is for reference only. I will continue to test it every week to see if there are any other problems that the technician and I may have overlooked.

Thank you.

r8wut
1st Gear
Posts: 66
Joined: Sun Aug 13, 2023 12:13 pm

Re: Car will not start

Post by r8wut » Sat Apr 13, 2024 9:46 am

Agree, with the statements above..

as our cars age, so does the likelihood of increased resistance / corrosion particularly with the various ground cables, points and connections.

Worst case scenario, I've seen first hand an ECU on another vag car we have - literally short-circuited and fail (read PITA + time consuming to resolve) - due to faulty / corroded earths.

I'll be addressing and posting my work on how to avoid this on the RS .. will update thread once I've done it

Meanwhile..
just checked the ground strap from starter to chassis, unbolted, wire-brushed, cleaned and re-tightened to ensure not loose, good contact / no resistance.
IMG_20240412_114834.jpg
IMG_20240412_151637.jpg
IMG_20240412_151641.jpg

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