924Board.org

[timsquare]

The story so far:

Bought this one recently, engine allegedly rebuilt about 8k miles ago, ran ok. Slight misfire at 4k, total power loss going round hard right handers. New plugs and leads cured the mis-fire. Fitting an in-tank pump (cut out by PO) seemed to cure the "can't turn right in a hurry" problem. Fitted a boost gauge where the clock should be just to see what was going on.

Easy starting, 10psi of boost on the gauge, (never reads vacuum though?) good power, no fuel level on the gauge, but otherwise - happy days. One serious test drive later:

cough, splutter, splutter fart, stop. "crap, run out of fuel" thinks me (no gauge remember). put some more in it. never run properly since.

I've tested:
Spark at all plugs
Fuel flow rate (in case I'd killed a pump)
MAP line to DITC (its there and seems ok)
seal on the charge tube to throttle body flange - knackered, but now 'fixed' as the two seal are NLA

It still starts on the button, idles fine but will not develop power, or run well off idle. Throttle switch working fine all the way back to the DITC connector, DITC plug just rebuilt. That said, when you pull the 'retard connector' (the crap fuel / advance at idle test plug) it does run much better. In this state it is at least drive-able.

Any ideas? please! any more head scratching and I will be bald. I thought it could be charge air temp sensor, anyone know what the curve for that looks like?
_________________
931 ('81 ROW)
120d (d - for 'devil's work')
748s (s - for 'stupidly expensive in clutches alone')

[ideola]

Not sure what you mean when you say "pull the retard connector". Unless I'm mistaken, the retard connector should not be connected for normal driving conditions. I'm wondering if fuel mixture and other settings have been mucked with to try to overcompensate for the retard connector having been erroneously connected by a PO.

The other thing that immediately springs to mind is to check the connection at the igniter (the little black receptacle on the inner fender well behind the headlight), and more importantly the large DITC connector at the silver box under the heater core. This large plug has multiple female receptacles that are just a press fit into male pins on the DITC box. They often get corroded or become loose over time. The connector itself has no means of being secured to the DITC box. Strongly recommend that you carefully inspect and service those connectors (clean them up, gently squeeze the female receptacles so they grip the male pins better) and firmly reseat the connector onto the box. I also recommend that you firmly zip-tie or rubber-band the connector to the box to prevent it from being able to back off on its own (or from vibration or getting kicked on entry and exit).

See if that helps...

...otherwise, conducting a proper CIS pressure test may be in order, as there could be a fueling issue that a simple flow test won't illuminate.
_________________
erstwhile owner of just about every 924 variant ever made

[morghen]

what do you mean never reads vacum? do you have a dial that should read vacum and it does not?
what about idle? what does the vacum/boost dial read at idle?
_________________
Supercharger and EFI kits
https://www.the924.com

[timsquare]

[timsquare]

Morghen,

by never reads vacuum, I mean the gauge scale reads -0.5 bar to +1.5bar, but sits at 0 at all times other than when the turbo is really spinning (ie 3000rpm +)
_________________
931 ('81 ROW)
120d (d - for 'devil's work')
748s (s - for 'stupidly expensive in clutches alone')

[timsquare]

[ideola]

[timsquare]

[ideola]

The connector should not be connected. Ever. Unless you can only get poor, low-octane fuel.
_________________
erstwhile owner of just about every 924 variant ever made

[Cedric]

Are you 100% sure about the connector dan?

You could try changing the coil and ignition module at the front (those are std and almost free, mines from a volvo 740 ). The module was broke on mine, making the car hard to start and ignition to be non consistent.
_________________
1980 924 Turbo
www.instagram.com/garagecedric/

[timsquare]

I might give a new coil a go, and have a look for an ignition module that is the same, just for something to do. I have spares off and old '84 NA car, think they are the same.

I keep thinking that if it starts fine, and idles fine, but goes horribly wrong as soon as you touch the throttle, maybe the DITC is sort of stuck in idle mode (so messing with the advance to try to maintain 950rpm). Seems unlikely though given that the throttle switch signal is getting to the pin on the DITC module.
_________________
931 ('81 ROW)
120d (d - for 'devil's work')
748s (s - for 'stupidly expensive in clutches alone')

[emoore924]

When you ran out of fuel, could you have sucked a bunch of crud into the fuel system and plugged a filter, injector or fuel dizzy. Seems too coincidental that you had a fuel-out situation coinciding with the failure to run.

I had a motor home break down just like this because a $2.99 filter on the side of the carbie got plugged up. It would run fine at idle but had no power. Some fuel was getting through but not enough to really run much beyond idle. Replaced the $2.99 filter and all was well.

[kcoyle]

Regarding retard connector;

From a "Smoothie" post:

The DITC box (digital ignition timing control) sits below-behind the radio. It takes input from the crank sensor, intake air temperature sensor, and a line from the intake plenum to its' built-in map sensor (to measure boost/vacuum) - from these inputs it determines the appropriate timing and tells the ignition trigger (on the front-left wheel well) when to fire. There's also a single-wire connector that lays over top of the left wheel well for use with low-octane fuel - disconnect the wire to retard timing by about 7 degrees (though you should find it's not necessary to disconnect it with a US 931 running regular low-octane fuel).



I'd do a CIS pressure test (system/cold/hot) look for loose stuff under the hood, and maybe check the air temp sender resistance for a start as well as what's been suggested.
Also, vacuum will be behind the TB, I'm tee'd in right under the TB to a port facing the front of the car.
_________________
1982 931- Stock with MBC at 8psi

Relax, all right? My old man is a television repairman, he's got this ultimate set of tools. I can fix it.

[Cedric]

You could always take the idle switch apart and clean and lube it. You should hear it click if you turn the throttle bewteen closed and slightly open. Could be nice just for a piece of mind. Its glued together but i opened it with a thin knife and then just glued it together when its was cleaned and lubed You could also measure if its switches as it should, just take the connector of and measure on the pins. Its just a simple open/closed switch.
_________________
1980 924 Turbo
www.instagram.com/garagecedric/

[ideola]