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914World.com _ 914World Garage _ Frustrated with D-jet----help please

Posted by: Porsche Rescue Jul 12 2003, 07:52 PM

'71 D-jet will not idle when hot. Poor throttle response coming off idle (acts like a carbed engine with no accelerator pump). Idle speed screw has almost no effect on RPM. Once engine gets going it pulls strong and smooth to red line.
ECU has no mixture adjustment. Valves, dwell and timing are correct (although dwell floats a bit with rpm, probably worn distributor). I have tested MPS and pressure sensor II and they meet B. Anders specs.
Cannot move any air through MPS by blowing. Throttle switch checks ok but I switched to another throttle body and switch anyway, no change. Replaced all vacuum hoses. Does anyone out there have any ideas? Don't say switch to carbs! "Not gonna do it, wouldn't be prudent" (#41).

Posted by: ChrisReale Jul 12 2003, 07:57 PM

How is the resistence on the CHT? Less than 100 when hot? You cannot properly diagnose an MPS by blowing or sucking. You need a vacuum gauge to do it

Posted by: Bleyseng Jul 12 2003, 08:14 PM

If the idle speed screw has no effect than there is another source of air (leaks). Also the timing could be off (too advanced) or caused by the worn distributor. The trigger points are effected also by a worn distributor causing poor injector timing ie bad idle/throttle response.

Readjust the valves
change the distributor to a rebuilt unit-$50
set the timing
check for vacuum leaks
Once you get these done, hooking up the retard hose back up should drop the idle down several hundred rpms. Then adjust the air bleed screw for idle.

The ECU's without a idle mix screw are tougher to keep the idle right on. Thats why they added the mix screw.

Geoff

Posted by: Porsche Rescue Jul 12 2003, 08:27 PM

Geoff, tell me more .....where do I get a rebuilt distributor for $50? Does it come with FI points?
The valves were done by local Porshce shop and timing set as well (they told me distributor bushings likely worn because dwell was not stable). I have checked it and it does float but stays within specs (44-50). Retard hose does drop idle as it should. Don't know where else to look for vacuum leak. I replaced all hoses. I suppose MPS could be bad but car sure runs strong from 2-5000 rpm.

Posted by: Bleyseng Jul 12 2003, 08:48 PM

Schucks sells them for $50, they are rebuilt by A1 Cardone, 1.7L ones only.

I would try that first before running around chasing FI gremlins. The distributor MUST be in good condition for Djet to run right.

Test the MPS for vacuum by sucking on the port and then sticking your tongue over it, if it holds real good then its likely to be decent. This won't tell your if it slowly leaking, if fact a leaker usually runs great cuz they are running rich. Lots of power in the rpm range you are talking about.

Geoff

Posted by: Porsche Rescue Jul 12 2003, 08:52 PM

From looking at the plugs I think it is running a bit rich. Guess I need to spring for a Mityvac (they are spendy little devils). I will go to Schucks tomorrow for the distributor. Only problem, if the MPS is bad, then what?

Posted by: Porsche Rescue Jul 12 2003, 08:59 PM

One more thing, if the MPS is bad does that mean it is supplying the air "leak" ?

Posted by: Bleyseng Jul 12 2003, 09:54 PM

If the MPS is bad the car will be full rich, like if the car was at WOT, 0hg of vacuum. At idle the MPS needs a good 15hg of vacuum to read right. So if the diaphram is cracked the MPS reads richer as there is Less vacuum acting on the diaphram. The diaphram controls the calibration of the mixture relative to vacuum, low vacuum at WOT, high a idle.
Geoff

Posted by: Porsche Rescue Jul 12 2003, 10:07 PM

So, if mine is cracked what next? Pelican says NLA. Try to find a good used one somewhere?

Posted by: MarkV Jul 12 2003, 10:34 PM

Performance Products spring 2002 catalog lists new one for 70-73 1.7 for $224.95, rebuilt one for $134.95. No new one listed for a 2.0 but they sell a rebuilt for $196.95.

Make sure you have a known leak proof vacuum source. I thought my MPS was bad, turns out it will hold a vacuum for 2 days.

Posted by: Bleyseng Jul 13 2003, 09:23 AM

Get a $15 vacuum pump from your FLAPS and pump it to 15hg and it should hold that for 5 minutes without much leakdown.

Geoff

Posted by: Porsche Rescue Jul 13 2003, 10:18 AM

I gotta do a better job of shopping around. Last time I priced a pump it was $50. Calling Schucks today for distributor (and a pump). Thanks

Posted by: Brad Roberts Jul 13 2003, 11:11 AM

I need to send all my MPS' to Geoff... if he finds a good one you can have it. I have about 8-10 1.7 MPS'.

I'm going to start giving away some of this archaic crap I have.

B

Posted by: Porsche Rescue Jul 13 2003, 11:51 AM

3 days for Schucks to get a distributor, A1 Cardone, $52. They also list one by Beck Arnley for $71. I went cheap. Will wait 'til I get distributor to get a vac. pump and check MPS. Don't throw those babies out Brad. Thanks to all of you.
I am trying to get my low mile (96K) all original non appearance group '71 running right so I can sell it. Need to raise funds (and use the space) to begin on my six this fall.

Posted by: Bleyseng Jul 13 2003, 01:34 PM

Send them up Brad, so I can recondition some of them.

Geoff

Posted by: r_towle Jul 17 2003, 05:58 PM

Could someone please let me know the phone number and web site for Schucks...

I am on the east coast...

Rich

Posted by: jdogg Jul 17 2003, 07:44 PM

Someone once told me that you could use a 1.7 distibutor in a 2.0. Said the the advance curve seemed to come in at lower rpms???? Any one care to elaborate? Will it just slip right in, trigger points and all??

Posted by: Porsche Rescue Jul 17 2003, 08:17 PM

Rich,
It appears to be a national chain. When I entered Schucks.com I got www.partsamerica.com. They showed the rebuilt 1.7 distributor for a '71 at $54.99 plus shipping. I didn't check for a 2.0. I haven't picked mine up yet but their online picture shows vacuum diaphragm and fuel injection points installed. Hope this helps.

Posted by: Bruce Allert Jul 17 2003, 08:38 PM

Jim, why not put my MPS on your car to see if that is the problem? It's a 1.7. Wouldn't that eliminate one problem? If it runs better then you don't need the dizzy. Does the 71 swap out with parts from a 73? Could even try the dizzy & see if that works. I have new Pertronics in it and new TPS too.
You could call it a "Swap Meet"
bruce

Posted by: Porsche Rescue Jul 17 2003, 08:43 PM

Thanks Bruce. I need a distributor regardless. The pros at Stuttgart Autotech said mine was bad. But I have a feeling that won't solve my problem entirely. The MPS is the next suspect. I will check B. Anders data and if a '73 1.7 will work on a '71 I just may take you up on your offer. Maybe I'll know something by Sunday.

Posted by: Bleyseng Jul 17 2003, 09:11 PM

A 1.7 MPS is a 1.7 MPS so try out Bruce's to see if that helps.

Geoff

Posted by: Porsche Rescue Jul 17 2003, 09:21 PM

Geoff, just checked Anders' chart and he agrees with you on the MPS. Guess I'll take the cover off TPS after I install new distributor. Did you notice that your Schucks reference has made it to the east coast? Wonder if they pay a commission?

Bruce, let's talk about the transplant on Sunday.

Posted by: Bleyseng Jul 17 2003, 09:30 PM

Yes, you can run a 1.7 dizzy in a 2.0l. Yeah, its not EXACTLY the same advance curve but give me a clean spark and injector timing over a POS one anyday.

Geoff

Posted by: Bruce Allert Jul 17 2003, 10:30 PM

Hey Jim, sounds like a plan. We'll get to the bottom of yer troubles! even if we gotta stick my whole engine in there! (oh... guess that won't solve anything, eh?)

bruce