Manuel928S4

Hi, everyone
I have an 88 S4 and last night I was in a drive through and my car completely died. It was a sudden shut down of everything, like if you took the key out of the car and removed the battery cable. The only thing working were the interior lights, which were dimmed. I disconnected the negative battery terminal and the car wouldn't respond for about 30 seconds after putting my key in the ignition and, then, turned on like nothing happened. After that, I headed out and, when my car was in idle again, the same thing happened.

I think this was unrelated, but today the car suddenly started running on 4 cylinders. I shut off the car for a few minutes and the car ran fine. The car did the same thing about 5 minutes later. I was able to replicate the symptoms by disconnecting one of the ignition modules. I haven't had any time to try to replicate the symptoms in real life again.

I suspect the shut down was related to the alarm system, because it's the only thing I can think of that would entirely disable the car. I dont think a faulty ignition switch would disable even the hazard flashing lights. If anybody could point me to what I should start checking, would be greatly appreciated.

Thanks in advanced,
Manuel

Speedtoys

Make sure the battery cables are all tight, all three.

Also, your ground cable could be very suspect as well, look at the ends, anything white or green? Look under the insulation.

Engine ground can suck really bad as well.

Might be a good time to ask, when was the last time ALL of the main chassis grounds were cleaned being in PR?

Manuel928S4

Thanks for the quick reply! I cleaned all of the chassis grounds, except the engine ground, a few months ago. I guess I will look into that. Also, I have been meaning to replace the battery ground strap, even though it looks ok. I will do a resistance test tomorrow just to see if there is anything obvious there.

Thanks,
Manuel

Speedtoys

And the positive wires off the battery, there are more than 1..and they have to be clean and tight.

FredR

What do you mean by a "drive through"- presumably an automated car wash system?

Water ingress will not harm an earthing system- quite the opposite!

A faulty ignition switch most certainly can bring down the entire engine management system as the switched "bus 15" is needed to power up the computers and energise the relays that switch power to energise the engine management system. Water flying around left right and centre could theoretically cause a power disruption as there are live, non-fused connections on the starter motor, the alternator, the ABS post and the hot post. Water should not be able to permeate at these positions but...?

Is your car equipped with cats? Loss of ignition on 4 cylinders is usually associated with one of the ignition protection relays shutting down for whatever reason. The sensors are located in the cats and if water gets into one of them the system may cause a shutdown of one of the two circuits. These relays, located next to the computers, have an LED that illuminates if this happens- one is green the other red and that tells you which cat sensor is involved in the event.

A problem with the ignition switch should not shutdown 4 cylinders and neither will an earth fault.

Petza914

Fred, by drive through, I think he means where you pull up to pick up food, like a McDonlads restaurant.

Based on the symptoms, the electrical part of the ignition switch could also be faulty if it's not a ground issue.

Speedtoys

88 S4 has this protection system?

FredR

Jeff,

Not sure when cats where introduced in your neck of the woods- not over here for sure!

However, when i hear of a S4 running on 4 cylinders one automatically suspects cats and the protection relay circuits. They were fitted on MY90 and possibly MY89 but MY88?

FredR

Hi Pete,

I was wondering if there was some significance as to why the specific location was reported and figured a car wash might have a contributory capability- use of English also varies considerably across the world.

mb911

Sounds like the safety feature is more a hassle ?

Manuel928S4

Fred, by drive through I meant like a Fast food drive through; meaning that the car was in idle for a while.
I originally suspected that but, from my readings, the safety deactivation was introduced in 89. I’m currently working, but when I got here, the car shut down the 4cyl again while I was parking the car, so I guess I’ll find out if the LEDs are red or not.

Speedtoys

Nothing runs well if you have badly maintained ground straps and battery + power leads.

Takes 10min to make sure they're all tight and clean, result?

FredR

Hi Manuel,

Given I am "English English" our use of the language can vary some compared to your side of the pond. I wondered if there was some implied connection between the circumstances and what happenbed but clearly not the case.

Regarding the first event- the ignition switch could cause something like you described- these items do fail and unpredictably so but many exist flawlessly for years on end.

Regarding running on 4 cylinders a final element failure would cause the engine to run on 4 cylinders- how probable such an event is remains to be seen. These units can and do fail with age - whether they would fail intermittently on their way out I cannot say- hopefully other listers will chime in if they have experienced similar.

Checking the main earth strap is a must do. As Jeff advised you, you need to pull back the black plastic heat shrink half an inch or so at both ends and take a look at the strands. When these things go they have broken strands, green oxidation and generally look awful. If they are in bad shape one can degrease them, brush some soldering flux into the joint, heat them over a gas stove and run in some solder. Roger does a non standard bulkier item. You also need to check the engine block earth strap located at the rear of the engine just behind cylinder No4.

Manuel928S4

Fred, no worries. My English is not the best. My native language is Spanish, so I apologize if I write something difficult to understand.

Well, im a bit embarrassed to say the running on 4cyl issue was just the coil wire that goes to the distributor. It seems like the insulation degraded, moisture got inside and corroded the end that goes to the distributor and, I’m guessing, it was enough that it got loose from vibrations. Im going to Check the resistance on all spark plug wires and, if there is any other one bad, I’ll order the set. If not, I’m almost sure I have a good used set somewhere and will change the distributor wire.

But (I think) this doesn’t yet explain why my car completely died while idling. Im just going to order the two grounds and change them. They’re way overdue changing.

Thanks a lot to everyone for helping!!

Manuel928S4

I also took a picture in the car’s natural state (with the hood open and a lot of swearing hahahah) when the car started acting up. Im sharing it because it came out pretty nice!
In all seriousness, this car is way more reliable than it gets credit for. All the issues I have had have been maintenance/age related. I haven’t had anything previously fixed go wrong again.