924Board.org

cjpurifoy924 · Joined: 06 Apr 2016 Posts: 21 Location: GREENVILLE, NC

Hello all,

I'm the noob who swapped the long block from an 82 N/A into a 78. I had started something that resembled a build log but after editing out all of the self deprecation and long, drawn out explanations of what I did wrong and the lessons I learned it comes down to this.... I have her running, though still not road ready. Big shout out to Mr. Ian for helping me get this far.

The symptom I have is glowing red headers with slight load. I have read this means I am way too lean, or combustion in the header, or crazy retarded timing.

Here is why I suspect the A/F ratio first. I built a fuel pressure gauge and tested things per the workshop manual and Dan's instruction thread. The numbers were good (I don't have them in front of me but they were close to spec). After a few oil changes to remove all of the fuel from the inside the block I pulled the injectors and did a flow test and observation. The flow rate was erratic, spray pattern horrible and one injector leaks and was humming/spraying as soon as the fuel pump was powered on. In order to get her running long enough to continue testing I adjust the cis down to where the injector stopped leaking then adjusted the bypass screw until I got an even idle. So I essentially have set the A/F ratio set to accommodate a known bad injector...and my need to have her running.

I have also had some distributor problems. For a long time I was chasing ignition issues. After working around the ICU for a while I finally found that the pick up coil in the dizzy was bad. The ohm test seemed to be OK from the ICU harness but later I pulled the dizzy and checked it out of the car. It was bad. I replaced it and she fired up willingly. However, I am not an experienced mechanic and may not have put the dizzy back together correctly as the first time I put it back together the timing was irrational. It would jump around as I revved up but would even out at idle. Due to my inexperience I didn't know if this was normal, a dodgy timing light or something really wrong with the distributor. I took it back apart and found that the vacuum advance lever had jumped off of the pin inside so the advance didn't know what to do. At least that is my guess. Currently I have the timing set to about 15+ TDC at 1000 rpm. Now it seems to be more stable but I have not taken her out on the road since the red header discovery and so I haven't had a run through the gears since the last dizzy rebuild....attempt.

I have not been running her for long periods since seeing the header turn into a night light. Just long enough to warm her up and troubleshoot the temp sensor and gauge. What steps should I take to troubleshoot this? I feel like injectors should be the obvious thing to replace but at the cost of $200 new, and my tight budget, I thought I would come and ask your opinions. What would you do first?

I have held off posting this because I suspect the first response will be "Buy new injectors and dizzy and call it a day." Also, just throwing it out there, I have a complete 1982 N/A (minus the engine) that I would be willing to trade or barter parts from if anyone has some injectors or a dizzy laying around. Just saying...

Thanks in advance for any help.
_________________
Best I can with what I got.

78 Porsche 924 n/a
82 Porsche 924 n/a

924RACR · Posted: Wed Jan 04, 2017 11:58 pm Post subject:

Yeah, you need to replace the injectors. Anything short of that is a waste of time and a risk to the engine.

As for the distributor advance, it's certainly possible (and not too bad a task) to fix the advance; I'd recommend also cleaning/lubricating the mechanism while you're in there.

But that's more base advance than you should run; in fact, that can also cause the overheat of the header. Dial it back below 10 degrees static; somewhere around 6-8 would be safe and not lose power. We run 12 on the racecar, but this isn't that, dial it back and keep it alive.

You may also well need to change the oil; that bad with the injectors can dump fuel into the oil and dilute it, compromising your lubrication system.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

RC · Joined: 25 Mar 2007 Posts: 2636 Location: Australia

15* BTDC is fine (I run 20-24 ECU stabilised) for idle. However it is total advance that matters, 40* @ 3-4K RPM is optimum. Disconnect & temporarily plug any vacuum lines, so you just use mechanical. Check the flywheel marks, note distance between 0 - 10* lines, IIRC 3.75 teeth, mark lines same distance with different colour marking pens, 20,30, 40*. Then check with timing light @ 4K, adjust so max adv = 40*. static should be ~15 anyway, Test & road test, hows that? Vac adv is purely for economy & emissions, reconnect & troubleshoot at your leisure. Retarded ignition will cause your symptoms.

Also check for exhaust system blockage, another common cause. Does your car have a cat?
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World`s quickest 924 2L slushbox

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11723 Location: PacNW

40° is way too much for a USA car. Vacuum signal adds another 10-15°. . .detonation city.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

RC · Joined: 25 Mar 2007 Posts: 2636 Location: Australia

Appears your comprehension is suffering there James.

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11723 Location: PacNW

Stand by for ignition curves from FSM.
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

924RACR · Posted: Thu Jan 12, 2017 6:33 am Post subject:

Yeah, we run 42deg total advance at high RPM - mechanical only, as noted, no vacuum devices in use on the racecar. Which works out to about 12 deg advance at idle.

Somewhat different mechanical curves, I guess.

An adjustable timing light is the best/easiest way to do it...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

Fifty50Plus · Posted: Thu Jan 12, 2017 6:51 am Post subject:

Same as Vaughan with my race car. No problems starting.
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

cjpurifoy924 · Joined: 06 Apr 2016 Posts: 21 Location: GREENVILLE, NC

Thanks guys. It's a beautiful day for wrenching and I have some parts to work with now thanks to Ian. I am taking my time and going through things while I have them apart. I will update with results and more questions I'm sure.

Thank you all for sharing your knowledge.
_________________
Best I can with what I got.

78 Porsche 924 n/a
82 Porsche 924 n/a

cjpurifoy924 · Joined: 06 Apr 2016 Posts: 21 Location: GREENVILLE, NC

Hey all. Short update here. Time has been short these last few months but I have been working on things as often as I can. I got a few parts from our forum friend Ian.

I have installed a dizzy (that I have not been inside of), some reasonably flow matched injectors, a tested coolant temp sensor, header wrap, updated exhaust and a wide band sensor. I also put the throttle body from the 82 on the intake. There may have been a problem with the throttle body from the '78 since I had the bypass screw bottomed out in order the get idle down to 1000. My friend and I checked compression and valve clearances and saw nothing out of place (he is a lot more experienced than I.)

Long story short I have reduced exhaust temps quite a bit by being able to lower idle, advance timing and ensure air fuel ratio's aren't too lean. The bursch header still glows after a good thrashing or if I hold rpm's at 2500+ for about 20 seconds but it will cool at idle after 5 minutes or so. It is likely 35+ years old at this point so I imagine it has seen some heat cycles and is pretty thin. I seem to have vacuum leaks around the injectors? Spraying starter fluid near them raises rpm's. Maybe the O rings need replacing?

Now that I have her running fairly well I feel that I need to go through all the pressure checks again. It likes to run lean when cold but evens out to 14.7 once warm. AFR reads 12.5 ish at WOT which I've read is a good sign. I have not invested in an adjustable timing light yet but it is on my list. I have quite the list now.

On another note. I don't know if he would want me to call attention because he is a pretty modest guy but Ian has been AWESOME in helping me figure this thing out. He has given tons of advice and even traded parts. He went so far as to pull his racecar to an autox event, WAY out of his way, and let me beat up on it in order to make sure the 924 fever doesn't leave me. That was easily the most fun I have had on four wheels. I can't wait to have mine road ready. Also, after having attended an endurance race with Ian I am seriously thinking about caging the '82 and finding another engine to put in it..... maybe a 2.5l from one of the 944's at a nearby junkyard? It is in bad shape for a road car but wonderful shape for a racecar.

Thanks again for all your help. I'll have more dumb questions soon.

Best Wishes
_________________
Best I can with what I got.

78 Porsche 924 n/a
82 Porsche 924 n/a

Fifty50Plus · Posted: Sun Apr 02, 2017 2:00 am Post subject:

Fix your air leaks FIRST! Your header should not glow at 2500.
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car