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914World.com _ 914World Garage _ Stock D-jet 1,7 running wery lean but why?

Posted by: larss Jul 9 2019, 01:30 PM

Have some problems with a stock 1,7 D-jet that runs wery lean, hunts and pops in the intake, hardly running at all....reving up wery uneven and slowly.

-Engine has not been running for severeal years so there is no history to tell.
-Timing triple checked 27 degrees at 3500rpm
-Fuel pressure triple checked 31psi
-All 4 injectors new (repro)
-Trigger points checked OK
-Changed to anoter MPS (which runs well in another d-jet) with no difference
-Changed head temp sensor with no difference
-Compression tested, even around 145psi
-Points, condenser, cap, cables are new (also tested with an old set but no difference)
-All injectors getting pulses, checked and injector plugs are at the correct injectors
-Yes firing order is triple checked

The only way to get it running quite OK is to replace the head temp sensor with a potentiometer at 3Kohms, runs quite good with that even when warm.
This leads me to think that it is running w e r y lean for some reason.

Any ideas?

/Lars S


Posted by: JeffBowlsby Jul 9 2019, 01:32 PM

Which MPS part number do you have, does it hold vacuum and has it been previously adjusted?

Posted by: larss Jul 9 2019, 10:51 PM

QUOTE(JeffBowlsby @ Jul 9 2019, 09:32 PM) *

Which MPS part number do you have, does it hold vacuum and has it been previously adjusted?


Thanks Jeff!
Sorry but the car is not neraby so I can not check tne MPS no at the moment but both MPS we have tested holds vacuum perfectely and still have the epoxi plugs and one of the MPS is borrowed from a car which runs good.

I dont know if I shall trust the new injectors flow rate beeing the same as the original yellow ones. They are bought as beeing a direct replacement however.


//Lars S

Posted by: BillC Jul 10 2019, 10:21 AM

Have you checked for a vacuum leak (or leaks)? Since you already tried a different MPS, looking for leaks is the next thing to check.

If the vacuum and intake hoses haven't been replaced in a while, start there. Also, check the intake manifold (the sheet metal piece that the throttle body mounts to) to make sure there are no rust pinholes in the bottom (fairly common problem, especially when the car sits for a while).

Posted by: larss Jul 10 2019, 10:45 AM

QUOTE(BillC @ Jul 10 2019, 06:21 PM) *

Have you checked for a vacuum leak (or leaks)? Since you already tried a different MPS, looking for leaks is the next thing to check.

If the vacuum and intake hoses haven't been replaced in a while, start there. Also, check the intake manifold (the sheet metal piece that the throttle body mounts to) to make sure there are no rust pinholes in the bottom (fairly common problem, especially when the car sits for a while).



Thanks BillC!
The hoses are all new and checked but as you mention vacuum leaks I suspect the PCV to feed a bit to much air...will check on that the next visit.


/Lars S


/



Posted by: larss Jul 11 2019, 08:57 AM

Short work on the engine today again...
Found out that the PCV was fully open all the time replaced it with a fixed 3mm orifice, idle came down a lot, now idles at 700rpm...but it didnt make any difference on the running, still wery lean, bucks and hesitates a lot when reving up, it can take some 5sec for reving up when opening the throttle.

Checked the throttle switch again, it gives about injector 20 pulses from closed to open and is well adjusted.

We ran it fully warm and adjusted the potentiometer (which we have replaced the head temp sensor with) so that it ran with good response. We must have the pot. on about 3kOhm, much less than that and it wil hesitate. 3kOhm corresponds to a dead cold engine!

Something is making the mixture way to lean but what?

(Sorry Jeff did not get the MPS no this time).

/Lars S

Posted by: JeffBowlsby Jul 11 2019, 09:32 AM

Besides the lean condition, are your distributor weights lubed and vacuum advance working?

Posted by: larss Jul 11 2019, 09:50 AM

QUOTE(JeffBowlsby @ Jul 11 2019, 05:32 PM) *

Besides the lean condition, are your distributor weights lubed and vacuum advance working?


Thanks Jeff,
Yes can see the marks moving to the rpms.รค
Have it spot on 27 degrees at 3500...no vacuim


/Lars

Posted by: JeffBowlsby Jul 11 2019, 10:07 AM

I was not asking about your ignition timing settings, but are your vacuum and mechanical advance functions working? If not it may be a reason for the lag in revving.

Posted by: larss Jul 11 2019, 10:27 AM

QUOTE(JeffBowlsby @ Jul 11 2019, 06:07 PM) *

I was not asking about your ignition timing settings, but are your vacuum and mechanical advance functions working? If not it may be a reason for the lag in revving.


Excuse me Jeff!
Vacuum advance working, checked by sucking.
Rpm advance checked by strobo.

Lars S

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