kzaenger

Hi,

I drove my 928 ('87 S4 auto w/ 76K miles) a couple of days ago and all was well. Today I went to start it and it turns over, fires up, then immediately dies. I let it sit a while and tried again and same thing...it'll turn over, catch, then die within a second or so.

I'd appreciate any thoughts on what could be amiss and where to start.

Thanks in advance,

Kevin

Randy V

The Occam's Razor question first: Does it have gas in the tank?

kzaenger

Well, it had plenty last time I drove it! There's no indication that it's a sprung a leak, but I'd have to verify that.

FBIII

If I were a betting man on less than complete info, I'd cast my vote for a faulty fuel pump relay.

Garth S

- which can quickly be confirmed by swapping in the horn relay (XII) for the fuel pump (XX) - provided that the horn works ...

Imo000

My guess is the fuel injection relay failed. I had the same exact thing happen to my '85 and my brother's 83. The engine would fire up for a sec or two then die. The fuel pump relay was good but the fuel injection relay was bad. If it was the fuel pump relay the engine might fire up for a sec but only once, after that it would not fire at all.

kzaenger

Thanks for the advice; I tried switching out the fuel pump relay to no avail. Then I tried the ignition relay...but I've tried cranking too much and my battery is too low, so I'll have to wait till later to see if this was the cause.

On a related note, should all the relays be the same? I have some that say 30A and some that say 40A...but the schematic diagram on each is the same. I switched out the ignition relay (30A) with one of the same to be sure. The only thing to note is that my ignition relay is the one with the fuse tester in it...which did work the other week when I was testing a fuse!

Thanks again.

JE928Sx4.

Don't rely on just swapping out the relay. Use a jumper wire first between pins 30 and 87 (?) I think it is. As I recall, you'll get the same problem if one of Relays IV, XVI and XXV (Ignition Relay-X 141.951.253.B, XVI EZK Ignition System (w/Fuse Tester) and 928.615.203.00 LH-Jetronic Fuel Injection 141.951.253.B respectively) are out as well. Jump them all to test first.

Same thing happend on the 86.5 I sold to a buddy, and it was the Ignition Relay-X.

JE928Sx4.

Ohhh.....don't forget the fuel pump fuse also, even if it's good make sure it's making contact (ask me how I know).

Bill Ball

Pray it is a relay, but find another 87+ 928 owner in your area and swap out the LH brain. If it fires at all and dies, it is not a fuse.

jserio

Yeah, I was thinking Brain freeze.

kzaenger

Tried swapping a bunch of relays, checked fuses and still no luck. I was able to get it to fire up and run if I held the gas above 2K RPM or so. But it didn't seem to be running very smoothly...and as soon as I let my foot off the gas it died. Anything else to check? Obviously I'm hoping it's not the brain! When the brain goes, does it just go? The car had been running fine up till today.

Thanks for the input.

Bill Ball

This sounds like the LH brain, but could be the MAF. Disconnect the MAF and see if it acts the same. I remember a failure like this where the MAF connection was the problem. Simply disconnecting and reconnecting fixed it. Here's hoping!

Brett Matthews

Hey kzaenger!
It is starting to sound like the problem I'm having with my shark! I've been posting about it, search under my 'list name for posts/threads to see what I've found, or I could email back and forth.

I had my LH rebuilt, and although it SEEMS as if that didn't fix the problem, that may have cured other problems I wasn't aware of..... Like, why was the fuel pump circuit from the LH bypassed....

My point is, to go at it from the other direction than I did; start with the least expensive checks or parts first!

Rickman@columbus.rr.com

Rich9928p

Kevin,

I've had several '87 and '88 LH injection modules in recently for rebuilds. Sometimes LHs die quickly, other times they die in many slow ways - death by multiple cuts. The multiple cut death is the worst scenario, because the car can stall and leave you by the side of the road, and then start up later. Shops can charge a lot of money chasing things down. Many shops aren't aware of the LH failure modes and make kludge repairs, such as wiring around the fuel pump relay. Sooner or later the LH always dies, and the mess is larger than ever to clean up.

I provide pretty detailed diagnostic steps for checking out many of the other possible problem areas for no start in the diagnostic section of my website www.electronikrepair.com. One of the LH failure modes is to inject way too much fuel - I saw that with Brett's and JE's LH modules. That can cause other problems downstream. Also, more than one component failure can occur at the same time.

A quick way to tell if your LH is dead is to plug in a known good LH from a friend or regional buddy's 928 into your car. If your 928 starts up and runs great with the test module, you've diagnosed the LH quickly. I test LHs as part of my service.