StratfordShark

I have an 88 S4 which fires instantly when cold and quickly reaches smooth idle, but is less reliable re-starting within a few minutes to a few hours after shutdown. Sometimes it will fire on the key only, but splutter for a few seconds before settling into smooth idle. Other times I have to catch it with the gas pedal or it will die. Running performance is fine.

Researching other posts/sites it looks like I may have one or more leaky injectors.

Have looked at various accounts of injector servicing/cleaning but as we're dealing with fuel here I'd really appreciate advice on best procedure to remove the injectors and test for leaks. Oh I also have a bottle of injector cleaner/fuel additive but just now I'm running my tank down so I can clean up/and or replace the fuel sender so won't use the cleaner for a while (it recommends adding to a full tank). I understand crud in injectors can cause them to leak too?

If I can diagnose leaky injector, do I just replace it or is it more likely to be leaking from hoses?

Many thanks in advance for advice,

Adrian
1988 S4 Auto Marine Blue

ZEUS+

Do you have a fuel pressure gauge ?

ibkevin

Why not just send them out to be serviced?

Uneven flow in injectors cause many problems.

douvillier

Install fuel pressure gauge, pressurize system, and see if your system is in limits, if it is and remains steady you have a another problem. If pressure drops, pressurize , clamp the delivery line and shut of the key. If the pressure remains steady the pump is defective because the check valve is bad. If pressure drops then pressurize system again and clamp the return line. If fuel pressure holds, the pressure regulator is bad. However, if the pressure continues to drop, an injector is leaking. Remove the spark plugs, one at a time, to locate the leaking injector. Of course my favorite is to pull the dipstick and try to light it, if it flames you have gas in the oil. Naturally I haven't tried that one yet.

borland

Yes, check the leakdown with a fuel pressure gage. The test is detailed in the WSM.

Another possible causes could be your MAF out of tolerance or faulty temperature sensor.

Also, try disconnecting the battery to remove any fault codes and allow the fuel injection brain to recalibrate the idle mixture.

StratfordShark

Thanks for all these excellent suggestions. I was wondering about the fuel pressure too. I don't have a fuel pressure gauge but presume it just pops into port at end of the line and would be handy to have one. At least I have the clamp! On the 88 S4 is the check valve integral with the fuel pump, so would need to renew pump if valve faulty?

This was I get to find if it's a leaking injector without having to actually take out injectors and look for fuel weeping, and the spark plug tip is smart.

Thanks again,

Adrian
--------
1988 S4 Auto Marine Blue

StratfordShark

[QUOTE=borland]Yes, check the leakdown with a fuel pressure gage. The test is detailed in the WSM.

Is there any reason why the manual recommends bridging fuel pump relay contacts to run it, as opposed to just turning on ignition with key?

Adrian

John Speake

If you just switch on the ignition, the fuel pump will not run. This is because the LH ECU will not energise the fuel pump relay until it receives rpm pulse from the EZK.

This is a safety feature, e.g if you crash and the ignition remains on (engine stalled) then the pump won't continue to pump fuel (into a possibly fracured fuel line).

UKKid35

[QUOTE=StratfordShark]The fuel pump will only run when the LH ECU detects a signal from the crank sensor telling it that the engine is turning over. This safety feature can be bypassed by replacing the relay with a jumper for the purposes of the test.

UKKid35

As ever, beaten by JDS!

UKKid35

Because the best quote you can find in the UK is about £25 per injector (just short of $400 for the set), not particularly good value unless you know that they are the cause of the problem.

ZEUS+

If check valve is defective, replace check valve. No need to replace pump.

S4-on-your-back-door

another way to check leaking injector jump relay let pump spool up until it shuts off , unbolt fuel rail
and pull it out with injectors attached (just anuf to see tips of injectors and watch them, if they drip than there leaking

Bill Ball

This works in concept, but the fuel dampners and some other parts are rigidly mounted which means you can't pull the rails with the fuel lines attached and under pressure. You'd have to remove the rails and jerry rig something with flexible lines.

We have some places here, such as witchhunter.com, that will fully service the injectors and provide new seals for about $15 per. Shipping to and from the UK can't be all that much.