1980 928 5sp no injector pulse ??? Help

[john 928]

Ok guys I got this 1980 that I've been working on and I thought I would of never got to where I am with the car. So far I have the car running on fuel down the throttle body.
I have checked fuel relay and the XV1 relay,I have 30 psi fuel pressure all the regulators are good. The aux air and cold start inj work with pulse.i checked the ecu and have power to all injector terminals 32,33,14.15 and power to afc terminals 10,29.
I have good ground to the ecu and all ground terminals 5,16,17,36 but no ground to the 02 sensor shield ground 23.
I have good ground to the 2 rt side valve cover grounds at this point I'm leaning towards a bad ecu.
Did I miss anything silly any help would great thanks guys
John
516-322-3422

[JK McDonald]

Hey John - Have you seen the car run previously or is this a new project to you ? Although the computer can fail - they are pretty tough. Make sure to check and clean all the critical fuel computer ground terminals just above your fuse/relay panel, inspect the computer connector plug and the injector harness for damage.

Since it sounds like you have a reasonable spark and the signal from the distributor (green wire) to the ignition unit is good - If you have the cold start injector wired and plumbed correctly - as the starter turns the motor over it should try to run for a short period on the cold start injector.

Next - make sure the distributor (green wire) or "Engine Speed Pulse Signal" is also reaching the computer connector - Pin #1. This signal is used to tell the computer to alternately apply the fuel injector grounds in pairs. If the computer is correctly receiving the "Engine Speed Signal" a NOID LIGHT can be used to see a flash at each fuel injector connector.

One other point - make sure you have a good hot battery. If there is any question as to your battery status - add a second battery at the jumper post up front. There have been several instances where an owner has been chasing a "No Start" condition only to find out that it was a questionable battery or it's ground straps. If there isn't enough of the +12 volts remaining while the battery is being loaded by the starter - the fuel computer will not wake up.

Keep us posted - Michael

[john 928]

I have not seen the car run before I got it. It was sitting under a tree for about 4 years. I replaced the green wire with a new one and put a new battery new fuel pump& filter drained and cleaned the tank and removed all injectors,rails and regulators and cleaned entire lines.i also replaced all the fuses,relays and cleaned the fuse panel. I also put a battery charger on it to start it while I'm working on it . The car does start for about 2 seconds then stalls. I have a niod light and get no pulse from any of the injectors

[john 928]

When you say pin #1 you are referring to the 35 pin connector
Ljet right that says engine speed from TZS 16

[JK McDonald]

Hey John - Yes - Pin #1 is the pulse that tells the computer that the engine is turning over. It sounds like you've gone through all the basic T/S steps.... Perhaps someone has a spare computer that they will loan you to verify whether this is the problem. I think I have one for a 1982 for an automatic transmission car - I'll see if I can find it. Not sure if the In/Out pins are correct but will do some research.

Michael

[john 928]

I have a 84 Atm parts car not too far from me. Does a 84s auto work on my 1980.
This is the part number on mine

[JK McDonald]

Hey John - I've dug through my spare parts storage container and have yet to find a working computer for an early 80's 928. I did find one marked dead - but I will check with a couple of friends who may have something. I'm not sure about the interchangeability of the computer from the 84 you mentioned.

I realize a missing injector ground signal is probably your major issue but just for some peace of mind have you pulsed your injectors using one of the little testers to make sure they are not stuck closed with old fuel ? Also check to make sure the AFC "door" is not frozen closed and moves smoothly.

There are many owners on this site with lots of 928 experience - I'm sure they will think of something you may have missed.

Michael

[john 928]

Thanks for looking. I ohm out the afc to make sure it was good and also swaped it with one I have in stock. When I pulled the injector rails off I took each injector and bench tested each one running carb cleaner thur them to rule out bad injectors. I went last night and checked pin #1 and had a good light pulse from my test light when I cranked the motor. I'm going to try a few things and see if the 84 ecu is the same
I appreciate the input and help
Thank you

[stepson]

I have a known working L-Jet computer I could loan you if you can't find one closer. You're only gonna need to borrow one for about 30 minutes, for gosh sakes. PM me your address if you can't find one closer.

[john 928]

Thanks guys
I have some local sources hopefully I can find one .
I'm starting to realize it's good to have lots of test equipment
Lol

[JK McDonald]

Hey John - I was going over some notes that I'd taken while helping to sort out another "No Injector Pulse" problem on a 1982 928 a while back. There is supposed to be a voltage stabilization circuit inside the ECU that can temporarily keep it's internal operating voltages boosted up (I assume some large capacitors) if the external battery drops below 9 or 10 volts during start. We'd determined that this circuit had failed and was dragging down the internal operating voltage in the old 82 computer I still have - marked bad.

Just a suggestion but you might test your ECU supply voltage during start just to make sure your external power source is over the 10 volt mark.

Good Luck, Michael

[john 928]

Thanks I will try that when I get home .
There are 2 12volt power pins #10 & #29
Both say afc relay xv1 87 should I check both
Pins?
Thanks

[john 928]

Here's a pic of the pin layout

[JK McDonald]

Hey John - You had stated early on that you had CHECKED the L-Jet Computer Power Relay XVI ? I thought we were well past this component but - for T/S purposes and to eliminate a potential relay problem make up a THREE WAY SPADE JUMPER WIRE. Remove Relay XVI from it's base and jumper socket pins 30 - 87 and 87 together (There is one (1) pin 30 and two (2) 87 pins in the internal relay circuitry). ..... This will provide a good solid +12 volts to the computer and tell you definitely if Relay XVI is or is not the issue.......

Also after rereading the rundown on some of your original problems - you mentioned that the two large resistors near the P/S pump reservoir were smoking. Just to eliminate a potential trouble spot, disconnect and clean the resistor terminals. Then verify that one reads (aprox) 0.4 Ohms and the other reads 0.6 Ohms. These are your voltage dropping resistors used to protect your coil during start and run. Don't mix their electrical wiring positions up.

Keep us posted - Michael

[john 928]

I made a jumper to 30 and the 2 87 spots already
And the same issue I also checked voltage at the 35 pin connecter
And with a fully charged battery I got 12.4 volts at both 12 volt terminals.
I will check those resistors but they cause a no voltage reading on the injectors?.
I was looking for a ecu and the part # ecu that I have they are saying it's hard to find

[JK McDonald]

Great - John you are definitely making good progress. It is often just a matter of completing a series of logical steps to check off what is working correctly before you will get down to the source of a problem. We have all had one issue or another chase us around a few laps as an unfamiliar car is brought back to life. There is a reason why such a limited number of these outstanding cars are in the hands of such a select few. The slack jawed 928 Porsche filling station gawkers are often still talking to themselves as we pull out and head back toward the on-ramp.

Continue On - Michael

[john 928]

This is so true, I always look for a good car with good history that someone gave up on and can't fix it and don't want to spend any more money because they can't fix it themself. This one by far has been a pain in the ass chasing all the electrical issues. But that's how you learn and the next one is easier to get running.
I love these cars and will always have one.
This one I think needs a ecu

[qdac]

Some of what I am going to say here is a GUESS. However, I have spent a LOT of time poking at and analyzing the L-Jet system on my 1981. I even bought and read the book!

The public opinion is that the controllers on the L-Jet rarely go bad.

My understanding is that the L-Jet ECU boxes versions .02, .03, & .04 are interchangeable. The .01 version (what you have) is SPECIAL, probably (GUESSING here) because the AFM was changed and presents different test resistance values between early models and the later models. If you change to a newer ECU, then you should consider also changing to a newer AFM. I can point you to the magic date stamp on the AFM if you need to see it to verify the model - it is HARD to find.

I don't know if the Temp II sensor differs between the L-Jet years. Please look it up. These three (ECU, AFM, and Temp II) should probably all be for the same year. VERIFY THE WIRING. It might have changed along with the ECU/AFM change between the .01 and .02 versions.

I found a spare .03 ECU on e-bay cheap and I have swapped between the .02 and .03 versions on my 1981 (with the newer style AFM) without any apparent change in behavior. My AFM is definitely the newer version.

I don't see many .01 or .04 ECUs on e-bay. Maybe those cars don't get parted out as much. You may have problems finding a .01 ECU if yours is bad - but this is unlikely.

I feel it is more likely that your AFM is having troubles. There is a 944 web site that discusses testing and tweaking these items. Google it.

My understanding is that if your Temp II is bad or disconnected, your engine will run so rich that it will not fire. Verify this.

Check spark timing - I had to remove my distributor for other work and I re-installed it one tooth off. It didn't start.

A lot of people on these boards claim that their engine fires for a second and then dies. My GUESS is that they are running off the cold start injector and that their ECU isn't doing its job. Are you seeing this behavior or are you not seeing any fire at all?

Good luck with this - I had the advantage of starting with a running system and so it was easy for me to make a change, look at the effect, and then make a decision on what to do next.

[john 928]

I can say that it runs and stalls on the cold start but I still have no injector pulse. Your saying of the distributor is off I won't get any injector pulse when everything else tests good. I swaped out the afm with a 84 and no change. I will check the timing by I think I'm chasing a bad ground or bad ecu.
So your suing if my temp 2 is bad I won't get injector pulse?

[JK McDonald]

Hey John - How is your search going in locating a L-Jet 928-618-106-01 computer ?

From one of my Bosch Fuel Injection Control books it looks like the slight difference between the 1980 - 1984 computer P/N includes some of the external inputs and/or sensors. There are naturally some electronic tweeks internally as well - but the last two series digits (01, 02, 03 and 04) primarily designate variances between the early vs later performance, emission spec's, AFC calibration, timing, acceleration curves, etc..... Your computer 928-618-106-01 provides for the earliest set up. Although there is no indication mentioned in the results of updating your car to a later series I'd assume that you need to at least stick to the correct auto/std transmission.

As a last resort there are Bosch Service Centers on the internet that can repair your computer. They would also be able to provide a definitive answer as to cross reference part/series information.

One other static test that you might try (if you haven't already) is to use an ohm meter to check the resistance BETWEEN one of the computer ground pins (pin 16) and each of the output injector ground signal pins (14, 15, 32, 33). If there is a very low resistance reading between each pair of pins (16 - 14, etc...) it's output amp is damaged or shorted.

I don't think qdac is saying the distributor being off a tooth or the Temp II sensor would prevent the injectors from getting the ground pulse. Qdac was faster than I was in providing some good information...

Good Luck, Michael