Volvo 1800ES D-Jetronic MY73

Hi Pierre,
I think you mean it closes when the throttle closes?

Regards
Norbert

Yes Norbert, but now I have a doubt... I'll check again 

So I can confirm that the idle contact closes at idle. Thank you Norbert for your correction.

About the engine hesitation, I can detect it just by opening the throttle : the engine revs with a small delay (a fraction of second). I tried to increase slightly the fuel pressure (2.15 bar instead of 2.05), it is better. So I was wrong : this hesitation was due to a slightly lean mixture. Maybe a very little more fuel pressure (2.2 bar) and it will be perfect. The accurate manometer is very useful in this case, to adjust precisely fuel pressure.

But even without this ultimate adjustment, the engine runs smooth and noise is low.

Another point : fuel consumption is now very acceptable. This is due to throttle sensor right adjustment and correct wiring of cold start loop. And as a consequence, cold start occurs quickly, just by turning ignition key, in roughly 1.5 second. 

I may be not too far from a very satisfactory tuning 

Hi Pierre,

if your car runs too lean (which you do not know as you do not measure exhaust) it is not the correct way to play with fuel pressure. You should find the real problem starting from engine mechanics and ignition.

So...
Following your advices, I set fuel pressure to 2 bar. This is not a adjustment lever for mixture.
I have found the reason of engine hesitation : on B20E, engine vacuum adds a negative advance. It seems that the negative advance was too high, although initial advance setting was correct. So, instead of trying to make the Bosch vacuum device work properly, I installed a 123ignition distributor. Works like a charm. Advance initial setting is 10 deg, with vacuum "advance" unplugged.
Good news : the gas analyzer works fine again. So I measured exhaust gas : 2.2% CO and 5.9% O2. Bad news, it's too lean.

On previous measurement, before tracking every and each problem, O2 rate was 0.8%. As I did not touch exhaust system nor intake system, I do not believe it is a false air leak that explain this 02 rate. It may be a mixture issue.

As far as I understood D-Jetronic, the devices that influence mixture are water temp sensor, air temp sensor and MPS. But those three devices work as enrichment devices. Am I right if I assume that those three devices can not explain a lean mixture ? Does a poor injection harness can explain a lean mixture ? I thought about ignition vacuum hose, so I installed a plug where the vacuum hose leaves the intake manifold : no effect on exhaust gases.

I also checked the injectors grommets, they are all fine. Engine compressions are ok, all above 10 bar. Valve clearance are all ok, checked twice, on cold and hot engine.

I'm a bit lost now... I can't understand how the mixture can be lean. The only explanation is that there is a false air leak that was hidden by an important enrichment. Now that I solved the enrichment issue, the false air leak is more visible. Or fuel flow is restricted ? I'll change fuel filter, to eliminate this possibility.

Any idea ?


 

Hi Pierre,

well I cannot confirm that engine and air temp sensor plus MPS only work as enrichment device. There is also an rpm influence via trigger contacts and acceleration pulses.

All sensors have the task to adjust the mixture. Both leaner and richer.