924 Not Chooching. 

"HFV has no HFV. But somehow has 2 motorcycles" (hondasfordsvolvo) 03/13/2016 at 21:54 • Filed to: None

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So last December my father in law picked up a 77 924, for literally nothing. A friend of his had it sitting in a garage for s few years and knew my brother in law, and I like to tinker with cars, so he gave it to us/my FIL.

Well we let it sit in storage till it warmed up a bit and we’ve now we’ve messed with it a bit. Here’s what we know.

1 It had about 8 gallons of brown gas in the tank, which we drained.

2. The fuel pump, was bunked, but we replaced it

3. It is getting fuel to.. what looks like a mechanical fuel pump (like a distributor, with fuel lines, instead of spark plug leads.

4. it will fire if you shoot some starter fluid in the throttle body

5. The darn thing won’t chooch. it won’t run.

So we’ve got air, spark, and we should have fuel. So my question to you Opponauts is, What’s next?

This is much prettier than out 924, but I feel like people don’t click articles without pics.

JR1 > HFV has no HFV. But somehow has 2 motorcycles 03/13/2016 at 21:58

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LS swap?

JR1 > JR1 03/13/2016 at 21:58

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Seriously though if you haven't already check a Porsche forum there info is invaluable

NinetyQ > HFV has no HFV. But somehow has 2 motorcycles 03/13/2016 at 22:00

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I have never heard the word “chooch.”

But yeah, the only other major thing is cylinder compression, but I doubt that’s keeping it from running entirely. Probably not even a problem. So you were getting fuel to that mechanical pump, but not beyond it? If so, that’s obviously suspect. If it’s getting to the engine, does it fire when you try to start it? When you spray starter fluid into it, does it fire and run for a second or two?

Basically, my biggest suspicions are that you aren’t actually getting fuel to the engine, and that even if you are, perhaps the timing is way off.

DrJohannVegas > HFV has no HFV. But somehow has 2 motorcycles 03/13/2016 at 22:04

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That’s one skookum piece of Swabian iron.

-this space for rent- > HFV has no HFV. But somehow has 2 motorcycles 03/13/2016 at 22:07

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Sounds like someone found a sucker to haul away his junk for free.

lone_liberal > HFV has no HFV. But somehow has 2 motorcycles 03/13/2016 at 22:14

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From a quick google it sounds like the fuel distributor (that’s what they call it) could use a good clean.

JasonStern911 > HFV has no HFV. But somehow has 2 motorcycles 03/13/2016 at 22:18

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Off the top of my head, there’s a high probability you aren’t getting the fuel that you expect. Likely causes are a clog somewhere you missed (injectors or fuel filter), a bad air flow meter, or mystical gremlins in whichever primitive Bosch fuel injection system the 924 used (L-Jet/K-Jet/etc.). Renntech would be a great source of information specific to the 924. Or you could just do the ‘Merican thing and throw away the fuel injection and run a carb. While I’m not a fan as a Porsche enthusiast, I understand the justification from a simplicity and cost/labor/knowledge standpoint.

If only EssExTee could be so grossly incandescent > HFV has no HFV. But somehow has 2 motorcycles 03/13/2016 at 22:24

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That is the most old-lady looking Porsche I have ever seen.

Dr. Zoidberg - RIP Oppo > HFV has no HFV. But somehow has 2 motorcycles 03/13/2016 at 22:49

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You’re right about the no pics no clicks observation. In fact, some of FPs posts are so lacking in actual content, they use animated gifs as lede images.

twochevrons > HFV has no HFV. But somehow has 2 motorcycles 03/13/2016 at 23:17

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The ‘mechanical fuel pump’ you mention is the fuel metering unit of the Bosch K-Jetronic (also known as CIS) injection system used by the 924 and pretty much every other German car from the ‘70s to the early ‘90s. It’s basically your air flow meter and control unit all in one.

I recently revived a barn-find VW Scirocco with K-jet, getting the injection system sorted out was the hardest part. Some things to try:

Change the fuel filter. No idea where it is in the 924, but K-jet is very dependent on fuel pressure, and a clogged up filter can easily cause enough pressure drop to really screw things up (and burn out your nice new pump).

Make sure that the injectors are flowing evenly with a good cone-shaped spray pattern. Pull the injectors out and put them in glass bottles, take the intake boot off the metering unit, and with the fuel pump jumped to power, lift the metering vane with a magnet – you should see a fine, even spray, accompanied by a distinctive whining sound from the injectors. If the spray is thready, or one injector isn’t flowing as well as the others, you’ll need new ones – K-jetronic injectors have a check valve in them (the control unit ‘switches’ the injectors on and off by adjusting the pressure to them), so they can’t be backflushed like normal injectors.

K-jet uses an extra injector (a.k.a. the cold start valve) spraying into the intake manifold that runs for a few seconds only on cold starts – if this (and the thermo-time switch that controls it) isn’t working, the engine will be difficult to impossible to start.

Is the auxiliary air valve working? There should be a hose bypassing the throttle butterfly, with a disc shaped valve in it – this valve should be open when the engine is cold, and if it’s jammed, you’re probably not getting enough air through for a cold start, and will need to hold the throttle open instead.

Was the fuel pump a generic one? K-jet runs at much higher pressures than a regular fuel injection system, and you need to have a pump that can cope with it.

Some cars with K-jet (like my Scirocco) have two fuel pumps, a low pressure pump in the tank, feeding a high pressure pump mounted outside. If the low pressure pump isn’t working, the high pressure pump won’t get any fuel to pump. Not sure if this is the case for the 924, though.

Due to its mechanical nature, K-jet has numerous moving parts with very fine tolerances that can gum up with old fuel deposits. Even after replacing the filter and cleaning the tank out, it may help to throw some cleaning additives in, and manually flow fuel through the system like I described in the injector test.

The biggest thing, though, is to read any and all documentation you can get your hands on. My experience is with the VW-Audi world, where the Robert Bentley manuals are second-to-none in terms of detailed, accurate service and troubleshooting information. As a start, here’s a Porsche document on K-jetronic as they use it, and a more generic how-it-works document from Bosch. The absolute worst thing you can do with K-jetronic is to mess around with it without understanding it – it’s a remarkably bulletproof system, but it doesn’t take kindly to neglect or uninformed tinkering. The information in those documents got my Scirocco from not starting at all, to running on two cylinders, to purring like a kitten; feel free to ask if you’ve got any questions.

EDIT: looks like you’re in MN – if you’re in the Twin Cities metro area, I’d be happy to drop by and lend a hand sometime.

twochevrons > lone_liberal 03/13/2016 at 23:20

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As somebody who has resurrected a K-jetronic equipped car, I would strongly caution against opening the fuel distributor to clean it – it’s full of springs and precision parts that need to go back together just so if it is to have any chance of running again. Pulling the injectors and manually flowing fresh fuel with some kind of cleaning additive through the system is a much safer option.

lone_liberal > twochevrons 03/13/2016 at 23:22

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Top tip!

Sam > HFV has no HFV. But somehow has 2 motorcycles 03/14/2016 at 00:30

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Take a look at the fuel filter. It should be in a canister on the side opposite the valve cover.

I have no idea what chooch means, but have you tried mashing the pedal a few times when you start it? Sometimes mine needs a little kick to get it going.

Flavien Vidal > HFV has no HFV. But somehow has 2 motorcycles 03/14/2016 at 05:32

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Carburetor conversion... That should simplify your life on a car with that much work :)

HFV has no HFV. But somehow has 2 motorcycles > JR1 03/14/2016 at 08:48

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I actually suggested that. my BIL wants to swap in an Audi 5cylinder turbo.

HFV has no HFV. But somehow has 2 motorcycles > Sam 03/14/2016 at 08:50

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thanks. chooch is a word this Canadian youtuber uses a lot.

JR1 > HFV has no HFV. But somehow has 2 motorcycles 03/14/2016 at 08:52

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Maybe go with the Audi. As much as an American V8 would be great in a Porsche it kind of feels like blasphemy

torque > twochevrons 03/14/2016 at 11:18

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this is a brilliant reply!

HFV has no HFV. But somehow has 2 motorcycles > twochevrons 03/14/2016 at 19:50

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Thanks for the info. Now we have lots of studying to do.