1990 S4 Auto ROW..
Recent battery (3 months),
Recent ground strap (1 year)
Grounds cleaned within last year.
Battery connections cleaned within last year.
Recent fuel pump (2 years)
Recent CE panel clean (2 years)
Intake refresh, hall / CPS, coils, distributors, plug wires etc. done a few years ago.

I generally keep my car on a battery tender. When dong so it usually (not always) starts fairly promptly (normal).
However, if It has been off the tender for a day (or less) I sometimes get a no-start. Car will start as per usual with a booster.

Yesterday morning I moved the car out of the garage to use the space to sort some items. It started well 24hrs later after which I drove it a short distance to go to a meeting. It started again in the normal manner 3 hours later.
I went to move it back into the garage a few hours after I got back home and no start. I could hear the fuel pump start up at ignition and again while I was trying to start it. It cranked strongly and for quite a while ( a minute or so over 5 or so tries) without firing or fade.
I put the booster on (hot post / brace bracket) and it started up as per normal.
This is not just an isolated incident. It has occurred several times over the last few years, sometimes after a hour or two running with a 15 minute stop, sometimes after an overnight stop after a 3 hour run. It does seem to be getting more common.

Any ideas what might be the problem? I have got into the habit of keeping a booster pack in the car whenever I am using it but am worried I might encounter a hard fault sooner or later.
I have spare LH & EZK computers somewhere in my stash but am yet to swap them in when I get the no start condition. (I am usually out somewhere when it does it or in a hurry to get somewhere).

I measured the parasitic draw recently which was 116mA for 20 or so minutes then dropped to 16mA. (Door lights off and relay removed)

Thanks
Myles

 

Bump!
Any ideas anyone?

 

If you have a spare LH unit the for sure you should be trying that to see if the problem remains the same or is somehow modulated. I doubt you have a MAF problem but needless to say they can have issues especially if there is degradation at the connector. The other common erratic problem source is the CPS [crank position sensor]. They can be a bit of a sod to get out and the connectors have a habit of crumbling with age- how old is yours?

 

Thanks Fred.
CPS was done a few years ago with the intake refresh.
MAF is old but wiring is in good condition.

I will try swapping in the spare LH and see if I have any issues. The problem is how long do I wait before I decide that this has resolved the problem??????? (I HATE intermittent issues!)

Myles

 

Myles,

A friend of mine over here had an issue on his S4. Did not sound like an LH type of issue in that it would start, run a bit and then die. We stuck in my spare LH and the car ran flawlessly. The more one can eliminate from the list of possibilities the closer one is to the solution. Stick in your LH and the same type of issue appears one can conclude it is not the LH. As to how long does one have to run the thing to make a determination well I guess that depends on how often the problem currently manifests itself.

If it is a wiring problem they can be real tricky to find. One can look at the things and they seem ok but all it takes is a weakness inside the wiring, at some point the thing fails to conduct adequately and all it takes is a pothole or a bump of some kind and down it goes.

 

Could be the hot water valve.



*I know thats not the issue, but it's how things are solved on the FB group these days*

 

Ha Ha.
I suppose I could just start at one end of the car and replace bits until the problem seems to disappear. Seems to be how a lot of mechanics work these days.

 

Myles,
Check your Temp II sensor also. Easy check and easy access. Temp II can make your car very hard to start.

 

John,
thanks for the suggestion.
The Temp II sensor is only a few years old. I would think that if it was a problem then I would still have the hard start issue even with jump starting.

It will literally go from turning over quite fast (as fast as would usually start it) with no firing to starting up immediately when a booster is added.

Myles

 

No start condition diagnosis always starts with:
- do you have spark?
- do you have fuel?

With a new(-ish) CPS, and assuming your observation of hearing the fuel pump during cranking (means you have a pretty loud pump...) is correct then...

... it still doesn't mean you have spark. Get a timing light or employ a 'ghetto method' (searchable) to ensure that you have spark when you are cranking during a no-start condition.

Do that and report back.

 

Also, Make sure the two LH harness grounds at the back of the block are both clean and tight. A loose LH harness ground will cause exactly the symptoms you describe and it's a stone cold bitch to figure that out by diagnosis.

Or, if you want to throw parts at the problem:
EZK, LH, and fuel pump relays
bolt coil wires (if you've recently replaced the plug wire set make sure you used the correct coil wires: the Beru sets come with two sets of coil wires. One is for
'old-style' pre-'89-ish (IIRC) and one is for new-style coils. The plug end for the coils is different.)
LH and EZK ECUs
both ignition amplifiers
both coils

Throwing parts is expensive which is why I recommend diagnosis even though it's a PITA on an intermittent issue.

 

Last but not least, buy steal or borrow a Bosch Hammer or the Theo Tool. Your '90 has the diag port and that makes life a lot easier...

 

Dave,
the fuel pump can be heard running for a moment when the ignition is turned on and for about the same duration once I stop cranking when it fails to start. Pump, filter, relay & in-tank pump are all reasonably newish.

I am pretty sure I have no spark but will borrow a timing light to have ready for next time it refuses to start.

 

Dave,
I know I did the two LH harness earths last round of maintenance on electrics. I will see if they are loose. Shame they are such a PITA to get to.
The wire set I got came from Roger and only had one set of coil wires. The problem existed before the new coils & distributer rotors / caps were fitted.

Myles

 

Dave,
I will see if I can track down either of those tools in NZ. I have not heard of anyone with one though.

Thanks for the advice and list of things to try. Like you, I would prefer not to just throw parts at the problem as it takes time and cost to get things from the USA.

I will report back once I have had a chance to check out your list (and the car mis-behaves at home again).

Myles