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This '79 turbo has a weird cold start issue. 3-4 second crank till it fires after 12 hours. Once it fires and shut down, it will star immediately up to 8 hours. Hot start is fine. Fuel pressures cold and hot perfect. Only the over night cold start. Checked fuel pumps, delivery rate above 1200cc. Drawing a blank. Anybody with similar experience?
The 930 has cold start enrichment, which provides fuel injection at certain temperatures. The cold start valve in the throttle body is controlled via the thermo time switch in the chain housing; the power supply comes from the starter. I would start there. It should be ruled out that false air is being drawn in somewhere and the control pressure of the WUR should be OK.
Fritz knows his way around a 930 (or two) so would start there. The other possibilities are the AAV and AAR (aux Air Valve and Aux Air Regulator) which you may only have one of these depending what 'spec' your car is. CA cars have both (ask me how I know). Both of these devices route fresh air around the meter directly into the intake manifold. If you have ever noticed how your 930 revs high on startup then after ~ 1 minute the idle automagically kicks down to normal (900 rpm). The AAV warms up when the car starts with a heating element inside and as that happens it closed a crescent moon shaped disk inside the device that shuts off this extra boost of fresh air on startup (cold). The AAR works differently but does the same thing. It is controlled by a thermo time switch mounted to the back right (looking at it) of the fuel distributor head. It is a pie shaped device that opens and closes with vacuum from the thermo switch - also at start up. I've included a photo of these devices for reference.
AAV and AAR have a very similar function, both pass air around the throttle valve direct into the intake manifold. AAV to support the cold start, AAR to avoid rich mixture when coasting.
The AAV is mechanically bulletproof even when dirty, but it can happen that the electrical heating fails. The AAV is then permanently open and the symptoms are completely different from the described: warm start problems and significantly increased idle speed. The situation is similar if the AAR has a malfunction.
Mine doesn't fire instantly either - take a few cranks - probably 8 - 10 cranks to get it to go. Seems like fuel pressure needs to build and the right mixture needs to be present then it goes. When it fires there is no mistaking it... no hesitation then.
I wouldn't say that 3 - 4 seconds is an “issue“, but a friends 930 fires up with the first turn of the starter, no matter how long she has been sat.
Anyway, the op doesn't seem to have any interest in the topic anymore.
Fritz
I am new to 930's, though have been wrenching on my 996 Turbo and 991 Turbo for many years.....
While I certainly understand all the words below, when I really understand the details of all that, plus where those parts are, plus how to trouble shoot them all, plus what makes sense to upgrade if any, I'll consider myself a bit more 930 competent!
Thanks at least for giving me a starting point. And even if the OP's interest has waned, thanks for posting up some great info!
Originally Posted by fritz k.
The 930 has cold start enrichment, which provides fuel injection at certain temperatures. The cold start valve in the throttle body is controlled via the thermo time switch in the chain housing; the power supply comes from the starter. I...It should be ruled out that false air is being drawn in somewhere and the control pressure of the WUR should be OK.
Originally Posted by David Delano
The other possibilities are the AAV and AAR (aux Air Valve and Aux Air Regulator) which you may only have one of these depending what 'spec' your car is... Both of these devices route fresh air around the meter directly into the intake manifold. I
Originally Posted by fritz k.
AAV and AAR have a very similar function, both pass air around the throttle valve direct into the intake manifold. AAV to support the cold start, AAR to avoid rich mixture when coasting.
The AAV is mechanically bulletproof even when dirty, but it can happen that the electrical heating fails. The AAV is then permanently open and the symptoms are completely different from the described: warm start problems and significantly increased idle speed. The situation is similar if the AAR has a malfunction.
This is my first post on RL having recently acquired an '86 US 930 i would like to prepare for possible Kjet and ancillary problems. I'd like to request for references to some of the best previous threads for the purposes of enhancing my knowledge for trouble shooting potential problems such as what was mentioned in this thread.
This is my first post on RL having recently acquired an '86 US 930 i would like to prepare for possible Kjet and ancillary problems. I'd like to request for references to some of the best previous threads for the purposes of enhancing my knowledge for trouble shooting potential problems such as what was mentioned in this thread.
Looking forward!
The search engine is your friend, you should be able to find multiple posts for just about anything you desire.
The fuel accumulator is intended to hold fuel pressure to the system in between starts and is a 'reserve' for high demand :-) times so as to not overwhelm the fuel pumps. If that is not operating at full intended capacity you could be slightly fuel (pressure) starved at cold start which would require more cranks to get the fuel pressure and accumulator up to full operating pressure. A minimum amount of pressure is required to push fuel past the injectors. Mine requires a few cranks usually as well and I think this is the issue. I will test it by replacing the accumulator.
I have the exact same problem on my 930 1984. Runs perfectly but needs a bit of cranking to start. I just seems she doesn't understand its a cold start the rpm are low when cold but runs well, so need to warm up manually.
would that most probably be the the cold start valve? Again runs fine also when cold it just doesn't start the cold procedure (i.e. 1200 rpm for the first couple of minutes) and needs cranking to start - at the moment I just go with full throttle and starts fine.
I have the exact same problem on my 930 1984. Runs perfectly but needs a bit of cranking to start. I just seems she doesn't understand its a cold start the rpm are low when cold but runs well, so need to warm up manually.
would that most probably be the the cold start valve? Again runs fine also when cold it just doesn't start the cold procedure (i.e. 1200 rpm for the first couple of minutes) and needs cranking to start - at the moment I just go with full throttle and starts fine.
thanks!
Not necessarily, and if so it's more likely the thermo time switch. But it can also be that the "cold" control pressure of the WUR is outside the specification and is therefore enriched too much. The control pressure increases after a few minutes due to electrical heating and then the problem is no longer obvious. I would check the WUR first.
09-15-2023, 03:12 PM
Cold start issue
the rpm are low when cold but runs well, so need to warm up manually.