AFARR

1984 928s Auto.

Picked up the car today--a project by any measure, but it looks like something I can handle (it was cheap, to boot). Before anyone says anything, I was on a very limited budget for a project car--almost got a 911 (70's) and saw this one. I can leave the car to sit as I get the spare funds for parts--I know parts can be expensive, etc. I probably would have never gotten a 928 if not for this one.

It had been driven up until yesterday--the owner had let it sit for an extended period, and wanted to make sure it would run for me. He drove it over the last couple of days.

I had planned on putting the temp tags on the car and driving home...wound up having AAA tow it here so I can work on it.

I put my own battery in it, had to use a jumper box (my battery came from a BMW and I had not had a chance to fully charge it).

Started right up.

Pulled out of the parking space (jumper box still connected, sitting in the trunk area of the car). Pulled forward about 20 yards to a parking lane. Parked the car to get the Temp tags put on the car (left it running to charge the battery)

The car suddenly stalled.

Tried to fire it up again, and got nothing.

Tried tapping on the Fuel Pump (looks to be fairly new, as does the fuel filter), no success. I was in a noisy environment, so I couldn't tell for sure if the pump was humming when the key was turned.

Tried several times, finally caught again, ran for about 2 minutes, stalled again.

Tried this repeatedly (including removing the Jumper box and hooking my other vehicle up to the car with jumper cables).

Very rarely would it catch and run for a minute or two (each time did seem shorter).

Finally couldn't get it to catch at all.

I did try the basic roadside stuff...pulled the fuel pump relay (and pulled the cover off of it)..seemed to be working (would click when the key was turned). Just now, pulled the EFI relay and got the same click when the key was turned. Checked all the fuses. Pulled the Distributor cap to check..some arcing on the interior with roughness on the edge of the rotor, but looked like it should still provide some spark.

The only unusual thing I noted was the dash volt meter never went above 12 volts, even with my '94 Explorer jumping the battery. Not sure how accurate the volt meter is in the dash, though. When you turn the key to 'Run', it shows about 10 volts. Once it started, it jumped up to just under 12 volts.

Any recommendations on what to look at first in the AM? I know I need factory manuals--I will get a set (figured on gettting the car home first).


Thanks.

I did a search for a similar problem, but most seem to be "runs then dies", not "runs, dies, won't start....runs, dies, won't start,......won't start...runs shorter, dies...finally, won't start at all"

Dave Howerdel

A relay, being an electrically operated switch, often fails in more than one way. Just because the coil operates properly, does not mean the contacts are good or that current is flowing properly(when a switch fails it can still be operated but the contacts are toast). The coil working is not a true test of the relay.
That being said, it sound to me that one of your relays is going bad. When it gets hot, it gives out. Cools off and works again. Make a jumper, and replace the relays with it one by one. If you find the one that's suspect, replace both and keep a spare.

AFARR

Question, though...I had the car towed here (over 2 hrs driving). Tried to start at that time, and still turns over but won't catch--should have been significantly cooled down after the drive.

Thanks--I will try the jumper thing.

Dave Howerdel

I've had cars fail the same way. What happens is that the relay, as it starts to fail, arcs upon closing, This arcing causes more and more carbon buildup on the contacts until the connection can no longer be made. Often a relay will buzz, caused by the contacts rapidly opening and closing, before it fails altogether(this is the contact on the end of the magnetized coil that pulls in the switch).
Sometimes relays can be cleaned but I've alway found it easier to replace them as the arcing tend to diminish the surface area of the contacts themselves.

AFARR

I would assume I should try the Fuel Pump/EFI relays first? Any other recommendations?

Jack Riffle

Your problem sounds like the AFM relay is bad. The car will start for a few seconds and then die. This is because it is running on the small amount of fuel provided by the cold start valve. When all fuel pressure is exhausted......no more start. Pull relay XV1 and jumper from the #30 terminal to the #87 terminal and start it up. Also, look at the bottom of the relay. If there are 5 male terminal there, then you have 2 #87 terminals and they must both be jumpered to the #30 terminal to make the car start. Yes, I know the WSM show only one #87 terminal, but for my 1981 L-Jet ( which is also what you have) there are 2 # 87 terminals. Let us know how you make out, and good luck.

AFARR

Jack,

I did pull the #16 relay (does show in the diagram 2 #87 terminals)--looked like it was working, but as mentioned above, I cannot be sure. I will try to jumper tomorrow.

I figure a run to RadioShack is in order--a bit of wire and some flat plug ends to make a jumper--unless anyone else has suggestions for a better design.

John Struthers

You jumped directly at the battery to start?

m21sniper

Sounds like the infamous fuel inj. relay



Pull relay number XVI and jump from terminals 30 to 87. If it's the relay it will fire up until you release the key.

That relay is unique to the fuel inj, and none of the other relays are interchangable. Get two of em from one of the big three, they're about 20-30 bucks or something. You'll want a spare.

Alternatively, try removing the relay cover and sanding or filing the contacts. A lot of times that will solve the problem too.

AFARR

John Strothers---yes, directly at the battery (+ to + on battery, - to Ground in battery box).

Garth S

I'm not sure what you mean by a 'jumper box' when referring to the BMW battery - is this battery fully charged and connected as the normal battery after cleaning the cars cable clamps and battery posts ? - including the wingnut /chassis connection of the ground strap? ( there have been some instances of the braided ground strap breaking within the insulation - so check continuity) Or is this some arrangment of a battery in a box connected to the car with jumper wires? If the PO was driving it - why change the battery?
These may appear inane questions - but starting at the last thing changed is often a good spot ....BTW, an invaluable tool is a digital multimeter.
If there is full power to the starter, then the above connections are OK; however, if there is a signifigant voltage drop, the injection brain ECU may well fail to function - even with a jumper hooked to a second vehicle .... BTDT

AFARR

Sorry to have been non-specific:

"Jumper Box" is one of those rechargeable (Gel battery, I would assume) portable boxes with 4 to 6' cables that you can use to help boost/jump start a dying battery--the place I picked the car up from had one rated at 600amps (I have a smaller unit at 400amps that cost $40 at home--I have seen some with a built in air compressor also).

After I used the jumper box and removed it, I put the traditional jumper cables connected to my car.

The PO had let the car sit for close to two years (hence the interior issues). Before storing, he pulled the battery. He didn't recall where the old battery got to, so he used one from another vehicle of his to get the thing driving (hence my bringing the BMW battery). I thought the BMW battery had a full charge initially--but it was too week to turn over the starter (hence the initial use of the jumper box).

I do have a digital multi-meter also at home.

Thanks!!

rixter

do not jump the car at the battery!!!

there is a jump post passenger side of engine bay, jumping from the battery can cause MAJOR electrical damage

m21sniper

I've jumped my 928 at the battery literally dozens of times.(i have one of those 3 day draws- 3 days sitting, and the battery needs a jump)

LOL.

AFARR

Quote: "jumping from the battery can cause MAJOR electrical damage"

OK, then what should I start looking at? Maybe that is also a cause.

I did look in the manual and see that there are directions for both the engine compartment AND rear battery for jump start.