'89 S4 Only starts sometimes

[Towers]

Hey All,

I'm trying to trouble shoot my old man's '89 S4 that is having start problems.

It's usually not bad when it has a fresh charge on the battery, but sometimes it refuses to start unless you put it in neutral and crank it and even then sometimes its iffy. It seems like it happens mostly when the car is warmed up, so I don't know if it's a relay or temperature sensor getting tripped or if it's just incidental.

I replaced the battery ground strap and it seemed better for a bit, but started happening again. I'm going to replace the engine grounds because I've read a few threads where it seemed like they were the source of unreliable starting, but I was wondering if anyone else had any ideas.

[1982_928]

Neutral safety switch, possibly? That's the only thing that i can think would have anything to do with having to put it in neutral.

[Danglerb]

Fresh charge doesn't tell us much, is the battery "good"?

Ground straps and relays can both be issues, but often its the battery.

[Towers]

I thought as well that it could be the neutral safety switch but someone told me it prevents the starter from turning at all so it likely wasn't the cause.

The battery reads a strong 12.5v on a voltmeter most of the time, but I guess I could have it tested.

[Mrmerlin]

if your testing the battery after it has been connected for a few weeks,
then there is a good chance it has been run down,

I suggest to disconnect the battery while the car sits.

Charge the battery with a 6 amp charger not a trickle charger.

hot start issues are caused by leaking fuel components,
a fuel pump check valve,
a leaking fuel damper or regulator,
or leaking injectors.

I suggest adding a bottle of techron and do lots of short drives,
also add about 6 oz of MMO to the gas to keep parts lubed .

Replace the starter relay with a brand new 53.
Get deoxit spray and spray all of the fuse/ relay connections front and back on the CE panel.
put some dexoit on the ground strap locations

[Towers]

In case anyone was wondering it seems like it was a combination of the bad battery ground strap and a dirty fuel system. The combination of a new ground cable and some fuel system cleaner has smoothed out the intermittent starts.

Now to fix the rest of this beast!

[Alan in AZ]

I have no idea what you are all talking about....

Does the car fail to crank? (starter does not engage) or does it crank without starting?

Cranking is NOT turning the key - it is the process of the starter rotating the engine... (like with a hand crank in the old days).

What you actually described is not the former case - but that's what all the answers so far relate to... please explain exactly what is happening.

Alan

[Towers]

Originally Posted by Alan in AZ

I have no idea what you are all talking about....

Does the car fail to crank? (starter does not engage) or does it crank without starting?

Cranking is NOT turning the key - it is the process of the starter rotating the engine... (like with a hand crank in the old days).

What you actually described is not the former case - but that's what all the answers so far relate to... please explain exactly what is happening.

Alan

Engine would crank (turn the key, starter goes round and round) but it wouldn't catch, turn it back off, put it in neutral and turn the key again, starter would go and vroom.

So the starter wasn't failing to crank, the engine was failing to start.

Since I changed out the strap and put in some fuel system detergent it hasn't missed a start.

[Alan in AZ]

Originally Posted by Towers

Engine would crank (turn the key, starter goes round and round) but it wouldn't catch, turn it back off, put it in neutral and turn the key again, starter would go and vroom.

So the starter wasn't failing to crank, the engine was failing to start.

Since I changed out the strap and put in some fuel system detergent it hasn't missed a start.

OK as I thought, you were mostly getting answers to a different question.

I doubt it was either of those though - unfortunately it will probably be back

Alan

[Towers]

Originally Posted by Alan in AZ

OK as I thought, you were mostly getting answers to a different question.

I doubt it was either of those though - unfortunately it will probably be back

Alan

Any thoughts as to what it might be?

[tisilrad]

given it was dependant on your battery charge you may want to check power going into your central electric from the battery , this line feeds from the battery positive terminal to the central electric to the yellow plug at the bottom of the ce panel.(it is a red wire i believe) If this line doesnt have full power it may have just enough voltage drop to not provide proper 12 volts...