Bjbpe

Hello again to all of you who are helping me to chase electrons in my S4. As an aerospace engineer for 50+ years I chased air and other fluids with abandon and stayed as far away from electrons (better known as Juice or electricity) as I could.

You fellows have been very kind in holding my hand while I timidly follow your advice. Dave, Stromius and others: I have squeezed my 180 pound bulk under the dash and pulled and checked the appropriate relay and fuse; they were both OK. I do have a multi-meter and swapped out to the horn just to be doubly sure. Everything checks.

So now I need to explore further. John and Schocki pronounced severe warnings about blowing the left hand ECU. In my feeble lexicography I take that to be the ELECTRONIC CONTROL UNIT which I really want to avoid sending it to an early grave. I would greatly appreciate any added information as to where the multi-pin plug is located.

Additionally Mr. Rpetty2 mentioned the pressure regulator (now we're getting into something I can appreciate) as well as the pump. Need a little clarification on "where", "what", etc.

Thanks guys. I hate crawling under this vehicle but I hate having to buy blown parts even more.

dr bob

Just to the right of where you wedged ypourself to access the fuses, the cover to the right of the passenger's feet hides a pair of controllers. The connectors are pretty well secured with those lever/latch mechanisms, but jack themselves clear when the lever is lifted. Just pop them loose, lift the connector clear of the little finger at the other end, and you can go to town with testing in the relay socket without worry.

But, before you get carried away there, spend a few minutes at the battery positive terminal. One big cable, and three smaller ones connected to the positive post. The smaller ones get loose sometimes, corroded a little sometimes. Loosen the smaller ones, and use a brass small brush to buff up the finish quality a bit. Assemble them snugly (~60 inch/lbs). Clean the main connector where it martes with the post, and the battery post itself. Tighten that to maybe 14 lbs/ft. Coat the whole thing with a film of Vaseline to block corrosive fumes.

Then start the car.


The pressure regulator is at the rear of the engine on the right (passenger) side under the bottom of the air cleaner housing. The left-side fuel rail has a damper at each end. There are vacuum connections to each damper and the regulator. Failure mode is a diaphragm rupture inside, allowing engine vacuum to draw fuel through to those hose connections. Try the sniff test on the hoses after a little cranking. Before disassembling any of that further, put a fuel pressure gauge on the front of the right side (passenger's side) rail and see if the pump is getting any pressure there. Putting a jumper in the fuel pump relay socket 30 to 87 should cause the pump to run. You should hear the pump (under the tank, right side, metal cover over it and the filter), and see 45-50 PSIG or so at the gauge on the rail. If no run, pull the metal cover off and inspect the wiring. If the pump runs, we need to find out why it runs but doesn't pump.

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One of our most (e)steemed local enthusiasts spent several days scratching his head over a similar set of symptoms, where the pump ran but wouldn't deliver enough to pressurize the system and start the car. The final remedy was to put a few gallons of gas in the tank. Gauge told him there was still a little bit in there. Pump told him otherwise.

Bjbpe

Thanks Dr. Bob. It's a new battery and the clamps were pretty snug when I replaced it but I'll give it a shot to be sure. Then I'll move on to your other suggestions.

SeanR

Just to add in case others are searching. Had this happen yesterday on a car that had been sitting for a few years (7).

Fuel flow was zero with the old pump so installed new pump and filter, car ran great for a bit and then due to a lack of flow died out. It was not consistent but once I put a pressure gauge on the fuel rail I could watch as I was in the drivers seat that when it started to bog that the flow was restricted. Pulled the fuel sender unit to see in the tank and what do I discover? The strainer was moving around at the outlet of the tank. So I pull the strainer and find that not only had it come disconnected from the insert to the tank, it had reversed its self so when the pump ran, it was shoving the closed end in to the pump in let.

Odd, but one of those things that can happen.

Rich9928p

I noticed that suggestions were to jumper the fuel pump relay socket, but no mention of what to where on the socket.

The 30 position of the socket is "always hot" .... there should be 12V (battery voltage) at the 30 position. If not, there is a problem between the battery position terminal and the relay socket. That is what Dr. Bob was talking about. The 87 position is what the high current side of the relay switches to, in this case the fuel pump. Since the 30 position is always hot and is not fused, care must be used.

If you look at the relay, there is a little schematic diagram of what it does, and on the bottom of the relay are the stamped pin position numbers. Compare the bottom of the relay to where it plugs into the relay socket, and you then see where the jumper wires should be placed ... between 30 and 87 positions.

This fact is also true for the LH relay and the EZK relays. These and the fuel pump relay are necessary for the engine to run. If all three relay sockets are jumpered 30 to 87, all the relay control logic is bypassed and the "most basic" conditions are presented to start the engine. If it starts, one of the jumper wires must be removed to turn the engine off because the ignition switch is bypassed!

Unplugging the jumpers one-by-one and inserting a relay will identify where the running problem is located ... if it dosn't run when a known good relay is plugged in, there is a problem with the control side of the circuit.

Bjbpe

Thanks to all for the various suggestions. Today I had success. For those who have been following my "won't start" experiences, you are probably aware that I checke4d out the fuse and relaw yesterday. The fuse was ok as was the relay (through a test of the horn). Since there was a hockey game on last night I closed up shop. Today I cleaned up the garage a bit (tools laying all over the place) and decided "What the hell! I'll give it one more try!" Amazingly, it started right up. So, the only thing I can figure is that either the fuse or the relay had a bad connection and the re-setting of those parts restored continuity. Hopefully I am past the problem as I'm hoping to get the car back on the road once the snowbanks disappear (it's snowing again right now so I have some time to fiddle with a few things.

Thanks again to all for suggestions. It would appear that the proble4m was in the fuse/relay. I still hate chasing electrons.

Dave928S

If it was a bad/intermittent connection then it would be a good idea to pull the fuse and relay again, and put a good corrosion inhibitor on the connections to ensure it doesn't happen again. Here is a link to a recent thread on that topic, with good products to use .... https://rennlist.com/forums/928-foru...-it-works.html

It would also be worth cleaning and re-tightening the two connections at the fuel pump, and earth points, which could also be giving intermittent connection.

Better to be safe than sorry .. and stranded somewhere.

Bjbpe

Thanks Dave. Gonna do that today.

Bjbpe

Just wanted to mention (for anyone's comment) what a difference the simple trick of cleaning the fuse and relay contacts has made. Over the 27 years I have owned the car, I guess I have gotten used to a very brief delay in starting the engine; not a big delay; probably no more than a second. Now, however, I barely twist the key and the engine is already running. For anyone who may think that their car is just a little slow in firing up, you might want to clean the contacts.

Dave928S

^^ Good to hear

Reinforces the common message here regarding cleaning connections and grounds. I had very similar symptoms to you on my GTS, which stranded me, and was fixed with a new fuse, relay, and clean connections. It's definitely worth following that procedure on all circuits that are vital to starting the car, as a preventative measure .. and a general CE panel and earth point clean and check.

Chalkboss

One word: DEOXYIT!

Bjbpe

As all can see, this thread is several months old and has not been active for two months. I've been using the car on a more-or-less regular basis but two weeks ago I had to spend time away from home as my wife was in a hospital in Colorado with a hip replacement. Warning to all you young fellows, at some point you're gonna get old; try putting it off.

Anyhow, while we were away, there was a hellacious thunder/rain storm in Wyoming. When we got back home, the weather was really damp and the car would not start once again. Given my wife's current physical health I didn't have time to trace the problem but, the next day, the car started once again. At this point I decided to buy a can of Deox.

Yesterday I sprayed the hell out of the entire bank of fuses and relays under the assumption of "What the hell, can't hurt". This morning I took the Porsche to work (yes, some of us old farts still put in full days!). Lo and behold, the car fired up instantly upon turning the key; fastest I've experienced since don't remember when. Amazingly, the radio and disk player have much better fidelity also and I don't think I am imagining this.

So, you guys have another convert to this bug juice and I hope I don't have to chase electrons for a long while.