My GTS was running fine and the next thing, the injectors stopped firing (next restart) ... so, I'm thinking relay ... I remember reading here that there's a harness wire that can be the problem near the rear of the engine, any ideas?

 

Heinrich:

A short in any of the injector leads can do this. I've seen twisted. frayed wires under the plug boots do this. That's the most likely spot for a short. Since all the injectors share a common ground, a short in one lead stops all of them.

Of course, jump the LH relay first.

 

+1 on LH Relay

You seem certain that the injectors are not firing and that that is the problem. Just to ask the obvious - do you have spark?

 

Check continuity between the two wires and continuity from each wire to ground.

The 12V supply for the injectors is from the fuel pump relay.

 

Thank you Bill, Sterling, DaveC and Matt. This is the direction I was thinking. OK I'll checkand get back to you guys. Dave, I am pretty sure this is the problem and yes I'll attend the relay first. I am 99% certain this is a relay issue, but you never know. Take care and thank you again :-)
Heinrich

 

Well, we have the LH relay clicking appropriately.
We have good fuel pressure.
We have good spark.
We have no Injector clicks.... Soooo...

We're gonna check continuity on the injectors.

 

If that's not the problem check your crank sensor under the MAF.

 

Ernie thanks, we'll check ... need to trace all those connectors anyway under the airbox. According to my friend who's working on the car, last thing he did between running and not running, was to instal the airbox.

 

If you have spark, the crank sensor is not the issue. I have a '91 S4 in my driveway right now with the same issue - injectors will not fire. Unfortunately, I'm busy working on my own car, but I'm watching this with great interest!

 

H..........under the air box/maf area there are a few ground wires that may have been disturbed; also the connection wires for the maf, the TPS and the IVS are all there also.

 

Sterling the relay clicks, but the injectors don't ... Malcolm, that is a possibility thanks.

 

The acid test is to pull the LH and stick it into one of your running S4's .... don't worry about MY - they will all interchange and run well enough for test purposes.

The LH relay may 'click' .... but all that tells one is that the trigger side of the circuit energizes via 86 - 86 to close the contacter joining +12v @ #30 to #87.
Swap relays to check, or alternatively, insert a jumper wire from 30 to 87. Another way is to verify +12v at pin #87 when the relay clicks

 

Since it hasn't been mentioned yet, it might be worth checking that clear ignition monitoring relay that the later cars have down by the ECU. Injector activation pulses from the LH have to go through that relay before they get to the injectors.

 

H--

Replace the FP relay and the LH realy with known good. The fact that the relay clicks just means it's "trying". Doesn't guarantee results. The 53B relays are too cheap to take a chance on, IMHO.

You can check the wiring harness from the protection relay socket by the LH brain, and at the brain connector itself. This is likely easier and faster than pulling fuel rail covers and risking more damage to crispy wiring under the hood.

The wiring diagram suggests that power for the circuit is applied to all injectors through the fuel pump relay, which receives battery power directly through a dedicated feed from the battery. Means it's one of the several smaller cables that attach to the battery positive terminal. Been in the battery well lately? If that feeder is disturbed, the FP relay may click but no power to MFI or the fuel pump. Is the pump running? The FP relay shares supply power with the MFI relay contact which feeds the LH module itself (via W23 ce connector to pin 9 on the LH connector). LH feeds power to the injectors via pin 18 in the connector. With the connector removed, you should test from 18 in the connector to ground and see an open circuit. If anything less, there's a fault to ground someplace in the injector wiring or in the ignition protection relay itself. Pull the relay aftre this test to be sure, since you'll want to do the next test there anyway.

The other side of the injectors is split between 1-4-6-7, and 2-3-5-8 at the monitoring relay. Pull that relay, and test from pin 5 on the relay socket to pin 18 on the LH connector. The resistance may be somewhere north of a few ohms, but not a dead short. Test from pin 2 in the relay socket to pin 18 at the LH connector, and the resistance should be the same as you measured from pin 5 previously. If one of these is less (closer to zero or actually zero ohms) you have at least isolated the problem to one set. If pin 5 is low, look at injector connectors 1-4-6-7; If pin 2 is way low, look at 2-3-5-8 connectors for shorted wiring.

If still no injection after these tests, poost back and we'll dig deeper.

 

Andrew: So am I, so am I

Paul Barrera '91$4 DOA (in Andrew's driveway)