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Hello all...don't frequent the forums much but was told by the FB groups to post here.
Background...I come from the land of 944 Turbos so this car is new to me. Finally got my first 928.
'81 Competition package. No injector pulse. I've ordered a noid light to confirm. Car runs on ether/starting fluid fine so spark is good.
Fuel pump/relay works and I'm getting pressure at the rail.
Switched power at injector plugs.
Injection relay works.
Cleaned DME ground on cam box under air valve.
Found two injector pigtail with broken wire casing and replace entire pigtails.
Alarm bypassed.
Welcome to the forums and congrats on your first 928 purchase! Please do a google search of rennlist and you'll see everything you need to know about L-jet starting problems, posted about twenty times! Just to get you started, though, the most likely culprits sound like the fuel injection relay (you can swap over other identical relays -- I think the horn relay is one -- to verify) and the two ground points on the passenger cam tower. I don't know how you verified whether the fuel injection relay works, so just do the swap. FYI, the L-jet system works by supplying 12V to the injectors full time and only the ground is switched to fire them... and that ground leads out to the two passenger cam tower connections. (Edit -- it sounds like maybe you got one of those grounds -- there are two). Also look through rennlist for care and maintenance of your central electrical panel, including all the fuses, relays, and all the colored connectors at the bottom. You might also want to check the giant connector at the L-jet brain in the passenger right footwell and make sure there is no corrosion on any pins.
With crispy and known injector wiring harness issues, it's also possible you have a short or disconnect somewhere. I posted a while back about which injector wires lead to which connectors and pins and the central electrical panel (and Ljet control box pins) if you need to do a continuity test -- but I'd try the easier stuff first.
Please share any further known history on the car -- when did it last run and then what happened?
Finally, if you haven't done so already, take a look at the sticky post above on FAQs.
The great news is that the L-jet system is quite robust and makes for a really sweet running car.
Good luck and keep us posted! Oh -- and it's kind of a tradition around here that you post some pictures of the car!!
Believe me, I've scoured the forums before posting.
I removed the cover of the relay and watched it physically actuate. I also swapped one in from a known working 951.
Yes, the injectors have power to them at all times and the DME pulses ground, I tested the injector pigtails and have power there. Both grounds are ok. Ive ordered a noid light to test ground pulse
Another thing ive noticed is that the voltmeter doesn't register until I tap on the dash, then reads very low. One battery i have been using is brand new and tests fine. The other is freshly charged. Could the dme not be seeing enough power to actuate the injectors or tell timing?
A low reading on the dash voltmeter is not good, but with the intermittent condition you describe, may also simply reflect a poor connection at the instrument cluster or elsewhere in the system. Ultimately it is not in the path to the L-jet system. You say you measured 12V at the injectors, so that's good. As a general bit of advice, the 928s seem to be sensitive to low batteries -- so always ensure you're testing with a fully charged and functioning battery. What's the voltage reading at the battery vs. at the injectors?
However, if you have a new to you car that is not running and has some known electrical issues, I highly recommend that you find the "Annual Electrical Maintenance" guide in the FAQ sticky and follow the listed procedures before going much further. Everything is a variable/unknown at this point on this car. Doing the recommended maintenance will help reduce the number of unknowns.
Also, as an FYI, power to the L-jet controller comes in through its pins 10 and 29. Those pins get their power from the separate/small wire harness at the battery, which leads in part to Connector V pin 4, which goes to Relay XVI terminal 30. When the key is in the run position and the relay is engaged, then power flows out to Connector X pins 2-5 which in turn power the injectors and the L-jet controller. (At least that's true on 83/84 models, generally the 80-84 systems are very close but the below link has additional resources).
I think you're on the right track to check for injector pulse. You can also try listening to them for clicking noise while cranking/running. The fact that the fuel pump runs is also good, though still a question mark without actually measuring pressure. Start with the basics and keep going, good luck!
Welcome! You will find everything you need here for your 928!
First, the FI relay is not the same as the "common" horn relay. (See attached, and print it out for your glove box.) It is its own part #. But it sounds like you've confirmed that yours is working.
Ignore your intermittent voltage gauge. It is a common problem, that is not related to your issue. Worry about it later.
Even after it is "fixed", never trust the pod gauge. Always use a multimeter.
rjtw is correct, your L-Jet is very dependent on great 12v+ and - going to the proper places.
At the battery posts your battery should read 12.5v or higher. At the jump post at least 12v.
Also critical to the L-Jet is good ground to the engine. Check and clean your ground strap (lower engine, passenger side), and the grounds to the cam covers.
If your car will run on starter fluid, the ignition and green wire are at least "ok" (not necessarily good, but ok). I'd pull the AFM and bench test it, and then very carefully check the plug and connector at the AFM for corrosion, and the existence of all 5 pins and plug sockets. The plug sockets will back out sometimes.
Oh, and it goes without saying, but I see it all the time...make sure you have good gas!
Report back on your findings and progress.
-Jason
Thanks for the correction about the horn relay, you're right!
And for anyone else following along, those fantastic one-pagers are available for other years here, linked in the other thread: https://rennlist.com/forums/928-foru...all-years.html
Starting fluid diagnostics are overrated. I used to use starting fluid for this, too. Now, I reserve it for my M1009 Blazer when the glow plug solenoid is disconnected.
I played helper to a L-jet 928 resuscitation that would run (run, not just hit) off of ether.. with the green wire broken at the distributor. As in it wasn't even touching the distributor. As it turns out, a new green wire was all that was needed to restore it to a running car. Let's also not discount that it might be possible to have a sufficient spark impulse through the green wire without the TSZ being satisfied to fire the L-jet. Or do we know otherwise? I don't.
I can only imagine how well the 32V engines, M28.11/12, and M28 21/22 will "diesel".
10-28-2019, 04:13 PM
oh boy, another no start thread!
