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Hello!
So, I am currently working on a 1979 928 with a bit of an interesting problem. I'm at my wits end and would love some help if anyone here knows whats up.
The car is immaculate and ran excellently as of last month. It got put up on stands to do some interior work, and during the process, the dash cluster was removed. When another guy at the shop put the cluster back on, he switched a couple of the large white connectors around and the dash wouldn't work correctly (needles bouncing around + lights not turning on).
I got my hands on it, switched the wires back around so the dash works fine now, and tried to get it to start. Unfortunately, it would crank, but not turn over.
I went ahead and checked the fuel pump relay, and it was dead. I'm assuming something getting switched around may have fried it? I don't have a new relay right now, so I jumped the pins to run the pump so I could still try to start it. The fuel pump runs great with a jumper wire.
I also pulled a spark plug to check spark, and it has excellent spark, and the plug isn't fouled, so I don't think I have any problems with ignition.
My big question is, what other electrical problem could have possibly happened to cause a no-start? It ran great last month and the only thing that has been touched was the dash.
Tyler that sure looks like a youtuber's car who seems to be an expert, but are the injectors firing? let us know and i'm sure you will get help here.
We are all at a bit of a loss here in the shop, as the Jettronic system in these cars is not something we're particularly familiar with. This car has the mechanical injectors in it, correct? How do I verify the injectors are firing? Do I crack the fitting at the intake manifold.
The help is appreciated.
Hello!
So, I am currently working on a 1979 928 with a bit of an interesting problem. I'm at my wits end and would love some help if anyone here knows whats up.
The car is immaculate and ran excellently as of last month. It got put up on stands to do some interior work, and during the process, the dash cluster was removed. When another guy at the shop put the cluster back on, he switched a couple of the large white connectors around and the dash wouldn't work correctly (needles bouncing around + lights not turning on).
I got my hands on it, switched the wires back around so the dash works fine now, and tried to get it to start. Unfortunately, it would crank, but not turn over.
I went ahead and checked the fuel pump relay, and it was dead. I'm assuming something getting switched around may have fried it? I don't have a new relay right now, so I jumped the pins to run the pump so I could still try to start it. The fuel pump runs great with a jumper wire.
I also pulled a spark plug to check spark, and it has excellent spark, and the plug isn't fouled, so I don't think I have any problems with ignition.
My big question is, what other electrical problem could have possibly happened to cause a no-start? It ran great last month and the only thing that has been touched was the dash.
Thanks in advance!
-Tyler
Try to start car with quick start fluid to see if it is purely fuel that it is lacking .
Detach air filter, spray quick start fluid when starting car. If it tries to run, it means ignition is OK but injectors are not spraying fuel.
Does the car not even try to start and dies after 1 sec ? (if it does, it means your cold start valve is spraying fuel but not enough since injectors do not spray)
The only thing I can come up with for your starting issue is the fuel pump relay. Does your fuel pump run ? You can try to bypass the relay by bridging connection 87 with 30 when trying to start.
Try to start car with quick start fluid to see if it is purely fuel that it is lacking .
Detach air filter, spray quick start fluid when starting car. If it tries to run, it means ignition is OK but injectors are not spraying fuel.
Does the car not even try to start and dies after 1 sec ? (if it does, it means your cold start valve is spraying fuel but not enough since injectors do not spray)
The only thing I can come up with for your starting issue is the fuel pump relay. Does your fuel pump run ? You can try to bypass the relay by bridging connection 87 with 30 when trying to start.
I did forget to mention in the OP that very occasionally when trying to crank, the car will sputter like it wants to start before going back to a dry crank. I will try with starter fluid and see what that brings.
And yes, I did jump the pump relay and the pump runs fine. Can I check pressure at the injecors by just cracking a line?
I did forget to mention in the OP that very occasionally when trying to crank, the car will sputter like it wants to start before going back to a dry crank. I will try with starter fluid and see what that brings.
And yes, I did jump the pump relay and the pump runs fine. Can I check pressure at the injecors by just cracking a line?
Fuel pressure (control & system pressure) needs to be measured on the WUR that controls your fuel pressures.
If you've run the pump with the engine not running you've likely pumped plenty of fuel into the cyl. I don't know how long you ran the pump, but with the pump running and the engine off, the injectors are squirting fuel at the idle rate. Quite possible it's well flooded now. Or - it could be not getting any fuel at all.
Here's how I would do it:
1. Remove all spark plugs, check for raw fuel, remove fuel pump relay.
2. Let car sit for 24+ hours.
3. Have a fire extinguisher handy, work in the drive way if you can.
4. Crank engine check all plugs for spark.
5. Replace green wire.
6. Repeat step 4.
7. Install all plugs if you have spark. If no spark, diagnose.
8. Install fuel pump relay. Crank the engine, see if it will fire on its own.
9. If it fires, then check for fuel leaks in engine bay. Final tuning will be needed later.
10. If it won't run, spritz carb cleaner in the intake while cranking, check it will run on carb cleaner.
11. If runs on carb cleaner spritz, and not on fuel from pump, remove all injectors. Attach inj back to the lines from the fuel dist.
12. With injectors removed from intakes, jumper fuel pump. Check each injector for buzzing, and fuel spray. Remove pump jumper.
13. Allow fuel on engine to evap. If you have NO or missing fuel spray and buzz from injectors, report back here for further info. You may press the large round air metering plate down SLIGHTLY to see if fuel spray increases. Be careful, raw fuel on engine!
Ignition Box? I had a similar problem once. And I Changed the ignition box and it fixed the problem. When you open the hood its stuck to the left wing. Its kind of hard to see.
Best to go back to the last thing/area you worked on as the source of your issue is most often there. Once you have the instrument binnacle out check the condition of the ignition switch wiring harness and plug. If that all checks out good, verify voltage at terminal 15 on the fuel pump relay socket when the engine is cranking. If no voltage when cranking the ignition switch is likely bad or there is a break in the wire from the switch to the relay. As a matter of fact, I'd probably install a new switch WYAIT if there isn't any record of the part being replaced. The switch is a known wear item that will cause all kinds of strange issues when it starts to go.
Best to go back to the last thing/area you worked on as the source of your issue is most often there. Once you have the instrument binnacle out check the condition of the ignition switch wiring harness and plug. If that all checks out good, verify voltage at terminal 15 on the fuel pump relay socket when the engine is cranking. If no voltage when cranking the ignition switch is likely bad or there is a break in the wire from the switch to the relay. As a matter of fact, I'd probably install a new switch WYAIT if there isn't any record of the part being replaced. The switch is a known wear item that will cause all kinds of strange issues when it starts to go.
I checked the voltage at terminal 15 and found it was in spec. I know for sure that the fuel pump relay was certainly bad. Today, I did manage to get it to run on starter fluid, so I've narrowed it down to obviously a fueling issue. I'll definietly take a look at the switch too. I'm just confused as, it ran perfectly fine before it was worked on, so clearly something changed between then and now. I've checked pretty thoroughly over the instrument binnacle and can't find anything wrong, so more looking.
Did you get the correct relay with the extra small contact on it? If it lacks this and is just a normal 53 relay the car wont run easily if at all.
Replace your ignition switch as well while you're at it as recommended above. It will eventually fail and do all kinds of weird things before dying. Speaking from experience.
Also, the fuel pump relay gets the signal to run from the ignition computer, but seeing as you have solid spark it is probably fine.
Check your green wire as well if it is old. It should be a bright green color and is the common culprit of no starts and poor running.
Also verify your thermo time switch is working on the front of the engine. This is what fires the cold start injector and if it fails will cause very hard starts.
CIS also hates to sit so you should get a can of fuel system cleaner and run it through with the fuel pump jumped to clean all the deposits out. BG 44k is some of the strongest stuff for that.
The ignition box provides a second ground path to the fuel pump relay to energize once there is a timing pulse from the distributor via the "green wire" shielded cable. Power for the fuel pump relay comes from the ignition switch. As said above, install a new "green wire" from the distributor to the ignition box if it's age is unknown.
Based on your report I would suggest to replace the fuel pump relay, 928 615 113 01 XVII
the fuel pump fuse #22 its a 25A fuse, use good fuses
I would also install a new set of plugs Bosch WR7DC,
inspect the green wire if the connector ends are tan or brown then the wire is ready to be replaced
How many miles are on the car
So, as per advice in the thread, I replaced the relay and the green wire. Fuel pump works now, as the old relay was definitely bad, but absolutely nothing has changed otherwise.
I can run the car on starter fluid, so I know there is good ignition and spark.
I also checked the ohms on the thermo time switch. Everything seems within spec according to other threads on testing it.
I took fuel pressure at the Warm Up Relay, and I could only get ~20psi by cranking it over on the starter. I would assume this is acceptable, because running pressure seems to be around 30psi.
The car only sat for a couple of months, so I dont think the injectors would have had time to varnish up and stick. However, when I tried to crank it with one of the injectors out, it wouldn't spray into a cup.
I'm at a total loss, as none of us here know this system very well. Again, I would assume something electrical is the matter, but I know the fuel system is largely mechanical. Nothing on the fuel system has been touched since it ran last.
Guys.... I have a confession to make. I might be a bit mentally impaired.
Apparently, the car was run dry before it was parked and the gas gauge was frozen at 3/4 of a tank. I wasn't the one who parked it, so I didn't think anything of it.
Turns out it simply didn't have any gas. Put some in the tank, the fuel system primed, and she started right up. I feel incredibly dumb.
Thanks for all of the information, though. I've learned a lot about 928's, ha!
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No-Start Help
