Good News with DJet - Almost there!, Making progress... Options

[customstarr]

I want to start by thanking everyone for the input & assistance - I still be totally fuched if it wasn't for this web site, and the people that are dedicated to the 914. Anders site on the DJET system is an unbelievable resource. The 914 community has to be one of the strongrest and most knowledgable of any that I've been associated with in my years of the car hobby.

Finally got to the bottom of my rich running D-Jet issues - saved the best for last I guess. Timing and trigger points - that's what made the difference. Trigger points were dirty & timing slighlty retarded (like me I guess.) In the quest to solve this, I replaced and/or checked everything.

Here's where I'm at: Car is running good overall. It wants to die if I don't stay on the gas during the first 10 seconds of a cold start. After that, it runs stable with a low idle (500-600 RPM) - but it doesn't stall. I suspect a lean condition based on the info I've read. The idle improves as the engine warms, ultimately stabilizing at about 1K.

Since this is an early system (early 71) it does not have the enrichment knob on the ECU, and it has a 4-Pin TPS. I can't find any info on how to test/adjust the 4-pin TPS.

Wondering how I can verify ECU is recogizing idle from TPS (no method to adjust), and how to richen the idle? Toon has a 1972 FI system available- I'm wondering if I should switch to that to gain control over these things, or if there's a way to do it on mine. I haven't found that answer anywhere.

[JeffBowlsby]

Glad you have learned about D-Jet...its not that hard if you are methodical and understand the function of each component. Two contacts in the TPS contol the idle function in the ECU, you may be able to take teh TPS out the circuit and fake the ECU into idle mode if you know which two contacts in the TPS control it. Here is a link to the TPS calibration procedure if you have not found it yet:

http://www.pelicanparts.com/techarticles/9...ttle_switch.htm

[customstarr]

Glad you have learned about D-Jet...its not that hard if you are methodical and understand the function of each component. Two contacts in the TPS contol the idle function in the ECU, you may be able to take teh TPS out the circuit and fake the ECU into idle mode if you know which two contacts in the TPS control it. Here is a link to the TPS calibration procedure if you have not found it yet:

http://www.pelicanparts.com/techarticles/9...ttle_switch.htm

That's the problem - that procedure is for a 5-Pin TPS - I have a 4-Pin TPS. That's basically the only thing that I haven't been able to verify. If anyone knows how to set the 4-Pin TPS, please chime in.

[Bartlett 914]

Good to hear you made progress. I know nothing about the 4 pin TPS so I can't help there. Once that is ruled out and the problem remains (hopefully not), you could ass a small series resistor in with the CHT. I would use 25 to 47 ohms to start. half watt should be good enough. This will richen the mixture over the entire range.
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[Johny Blackstain]

Congrats (IMG:style_emoticons/default/clap56.gif) ! Trigger points are a serious PITA sitting @ the bottom if the distrib. I did not know your ECU has no knob... learn something everyday here on the world (IMG:style_emoticons/default/smile.gif) .


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[JeffBowlsby]

The contacts are numbered on the TPS and in the diagram. The only difference in the 4-5 pin TPS is that the 5-pin has a blank pin...its not used. Check the pin numbers and you will be good...

[Demick]

It wants to die if I don't stay on the gas during the first 10 seconds of a cold start. After that, it runs stable with a low idle (500-600 RPM) - but it doesn't stall. I suspect a lean condition based on the info I've read. The idle improves as the engine warms, ultimately stabilizing at about 1K.

If your idle is too lean, the idle speed will 'hunt'. In other words, it will not hold steady idle, but will constantly change from 500-1500rpm or so (without you touching the gas). If it doesn't hunt, then it is probably not lean.

Your symptoms on cold start are typical for a non-functioning AAR (Auxiliary Air Regulator). I'd bet it's not working. There are several sources to read about it. Here's one:
http://members.rennlist.com/pbanders/DJetParts.htm
Scroll down until you get to the Aux Air Regulator section.

Good luck.
Demick

[customstarr]

It wants to die if I don't stay on the gas during the first 10 seconds of a cold start. After that, it runs stable with a low idle (500-600 RPM) - but it doesn't stall. I suspect a lean condition based on the info I've read. The idle improves as the engine warms, ultimately stabilizing at about 1K.

If your idle is too lean, the idle speed will 'hunt'. In other words, it will not hold steady idle, but will constantly change from 500-1500rpm or so (without you touching the gas). If it doesn't hunt, then it is probably not lean.

Your symptoms on cold start are typical for a non-functioning AAR (Auxiliary Air Regulator). I'd bet it's not working. There are several sources to read about it. Here's one:
http://members.rennlist.com/pbanders/DJetParts.htm
Scroll down until you get to the Aux Air Regulator section.

Good luck.
Demick

Thanks Demick - I just started another topic on the AAR. I do agree that the AAR is probably my issue. When I cold start the car, the idle raises and then drops & continues the fluctuation up and down until partially warm. When I pulled & plugged the AAR to Intake line, the idle stabilizes - albeit low, but stable. The idle improves to normal when warm. I was under the impression that the AAR would just stick open or closed, but mine seems to cycle open & closed.

BTW - no vac leaks - tight as a whistle. And like I stated, pulling and plugging the AAR line & intake boot hole stabilzes the idle.

YES!!! I'm getting there!

[Demick]

Pretty much impossible for the AAR to cycle open and closed like you describe. More likely, when the AAR is open, it does cause a slightly lean condition which causes the cycling. When you plug it, that lean condition goes away, which stabilizes the idle, but also causes very low idle since you've plugged the bypass.

I'd still remove the AAR and check for full operation (goes from fully open when cold to fully closed within 10 minutes or so with 12V applied). Once that is confirmed to be working properly - or fixed if it has not been working properly, and if the fluctuating idle persists, then try to richen the mixture at idle.

Have you checked your fuel pressure?

Demick

[customstarr]

Pretty much impossible for the AAR to cycle open and closed like you describe. More likely, when the AAR is open, it does cause a slightly lean condition which causes the cycling. When you plug it, that lean condition goes away, which stabilizes the idle, but also causes very low idle since you've plugged the bypass.

I'd still remove the AAR and check for full operation (goes from fully open when cold to fully closed within 10 minutes or so with 12V applied). Once that is confirmed to be working properly - or fixed if it has not been working properly, and if the fluctuating idle persists, then try to richen the mixture at idle.

Have you checked your fuel pressure?

Demick

A little more investigation: After cold start, idle fluctuates with AAR connected - with it disconnected the idle is stable but low. At full operating temp, idle is low regardless of AAR status (connected/unconnected). Idle bleed screw has little to no effect on idle speed. Car runs great and it doesn't stall at a stop, but idle is very low (500 RPM).

Maybe it's also worth noting that even when the AAR line is unplugged from the intake boot (with the hole in the boot left wide open), the idle does not change (maybe lowers very slightly).

I checked the fuel pressure a while back (30 PSI), but I have to admit, it was with an el-cheapo Harbor Freight guage that felt like it was about ready to fall apart.