M4A3E2

So I have a '78 924 that I got running after 21 years off the road. While I've been daily-driving it for a week or so, I noticed it will do cold starts perfectly fine, and almost immediate hot starts fine, but if it sits for any period of time between starts (anywhere from 5 min to 2 hours) it'll just crank and crank for a long time unless I use starting fluid. Any idea where to start looking to fix this? Fuel pressure is good, and so is oil pressure.

Dan Martinic

1978? Really? Now that's cool! Sorry I can't help with your issue. Sounds like the heat soak changes something. Maybe look at coolant temp sensor

zoo

Sounds like you're not getting fuel out of the injectors. Do you hear them spraying if you open the AFM?

M4A3E2

Fuel is spraying, which is why I'm so confused. It does slow down on the cranking when it fires up finally, almost as if the ignition timing is too high?

Gage

Injectors leaking down? Check the oil for fuel smell.

M4A3E2

Pulled the injectors out to check if they were spraying, and the engine was popping out of the ports? Seemed awfully strange to me. I didn't disconnect the cold start injector though, just the switch. Could that have caused that little issue? After I reinstalled everything, it started right up.

M4A3E2

Checked the injectors again today, they were good. Cranked it, and there's a MAJOR vacuum leak, just replaced the lines but I think the air flow boot broke on the little side port it has.

Also, it still turns over VERY slowly when its actually firing up, whats up with that? It cranks fast, then slows down significantly when it actually fires up.

GPA951s

A Hot start problem Like that is Textbook Residual fuel pressure loss... Check valve by fuel pump.. might just have some dirt in it..

M4A3E2

Valve by fuel pump? Like at the banjo fitting, or the pressure accumulators?

Dan Martinic

I think he means the check valve attached to the actual fuel pump... #31 in pic

M4A3E2

Oh! Ok, I'll check that out as soon as my new o-rings arrive and this horrendous vacuum leak is sorted. I repaired the boot but something is still leaking and causing backfiring in the boot/injector seats.

GPA951s

Yup, losing residual FP Combined with heat causes vapor lock.

M4A3E2

Figured out the vacuum leak, giant PCV valve I left off. 3 different occasions today of me starting the car (11 am, 1pm, 3:30pm) and no issue at all. Once my fuel level is low I'm going to try and clean my check valve and see what that does to make sure there are no possible issues except maybe the DME, which seems to be working.

M4A3E2

Ok, so fuel system is clean and I am getting fuel, but it still refuses to do warm starts. The engine was cold enough I could rest my hand on it, yet it still didn't want to crank, left me stuck at a Kroger.
Series of events:
Go to car, spins over and sputters but no start.
Check vacuum lines, check relays and connections, check fuses.
3 blown fuses, replace all of them and just for funsies throw in replacement DME.
Battery is dead, get jumped but car still just sputters occasionally with no start.
Was like that the entire time till I just gave up.

At one point, I had no tach bounce at all! Then it suddenly started to work again? Car still refused to start.

M4A3E2

Drove the car and it just died today. Fuel pump was clicking but not spinning... Does this mean bad DME or bad pump?