Rich mixture.

Hi,

I just registered myself here on this forum, as a owner of 3 car equipped with the D-jetronic this is the place to be! I have 2 volvo's, a 142 from 1971 and a 144 from 1973. The 3rd car is a Citroen DS 21 from 1970. 2 car runs without problems but my 144 is a bit difficult one, bought in France it gave me several days of head ace. Burned exhaust valves, bad bearing and huge oil consumption. All that has been solved, now 1 problem remains, a rich fuel mixture causing the engine to preform poorly.
Tomorrow I'll check some parts, but I would like to know if a faulty MAP or throttle switch can cause a rich fuel mixture. Does anyone knows if that is possible?

Best regards,

Mathieu

Hi Mathieu,

a cordial welcome to oltimer.tips by Dr-DJet !

To answer your questions: Yes a detuned MAP sensor can very well cause a rich mixture. A faulty throttle switch can only cause it if it continuously opens and closes pins 9 and 20 in alternation. Rather less probable.

Hi Volker,

Thanks for the reply. This afternoon I swapped the MAP sensor for the one in the 142 that drives well. Now something weird happened, the stationairy rmp went up to 2200 revs and I was not able to get it much lower when the statsionairy adjust bolt was completely in. Both MAPs have the same number 0280100015. I drove some kilometers but the engine still preforms poorly. The rpm's stayed at 2000 revs. When I was back home I fitted the Original MAP sensor back and now thestationairy rpm's were back at 850 revs.
Have you any idea what can cause these difference in rpm's and what more I can check? I've already checked the compression of each cylinder, 3 were 14 bar and 1 is 13,5 bar. ( warm engine, throttle fully open) The 2 temperature sensors resistance were in the limits. Last week I fitted a brand new 123 ingition, so the triggerpoints such not be a problem.

Best regards,

Mathieu.

Hi Mathieu,

I had accidentially deleted this thread. But now I have restored it, hopefully completely.

Well I would make a bet: Your secoand MAP sensor that you swapped in is heavily leaking vacuum. Your 142 should consume a lot of fuel and run very rich then. A broken diaphragm increases the rpm of your car when you install it.

How did you fit vacuum for the 123 ignition?

Hi Volker,

A leaking diaphragm could be a reason for a high rpm, put when the engine of my 142 is warm the avv is closed and the stationairy rpm is 1000 rpm. I drove the car yesterday and the engine runs much beter than and the acceleration of the car is much beter. But off course it is possible that the MAP got broken when I swapped them. I measured the resistance of the coils in the MAP and there value were ok. Concern the 123 ignition, posseble something is wrong with the vacuum aswell, The distributor that was fitted has vacuum retard , and from what I understand the 123 has a vacum advance system. The supplier adviced me not to use curve 9, but 6 and to connect the vacumhose like it was on the original distributor. Do you know if this is right or do I have to modify something on the manyfold?

Best regards,

Mathieu.

Hi Mathieu,

if swapping those MAP sensors increases rpm, there must be a vacuum leakage that occurs when you swapped. The diaphragm of the MAP sensor swapped in was my hot guess.

Which Bosch no. does your old iginition distributor have? If it is 0 231 163 010 and you swap it with 123\B18-B20-R-V-IE, then you should not connect the vacuum line. I have described that here , but only in German.