Manifold Pressure Sensor

[J-M Reed]

I am looking for help with my fuel injection system. I have a Euro 1973 CSi and I've had it in a shop for several years now - mostly sitting there with the hood up and no one doing anything. Anyway - it went in for no wipers and window motors not working. Now those work but, of course when it was started (with gas drained and replaced) the fuel injectors all started leaking. Those were replaced along with plugs and wires as 2 wires were arcing. It starts and runs beautifully now until it gets to temperature and then stalls out. The mechanic did a smoke test to check for vacuum leaks, none, and he also replaced the thermostat and tested the temperate sensor (good he says). He also did a compression test and I have great compression. I read the online article (found through here) by Paul Anders on the Manifold Pressure Sensor and sent that to the mechanic. The thing I did notice about my MPS is that prior to my ownership the epoxy was drilled out. I have tried to find anyone in my area (Buffalo, NY) who knows the D-Tronic system to no avail. At this point, the mechanic and I have been in several arguments, with him adjusting the tuning to keep it running - which worked for a couple days, and him saying it may or may not be the MPS. At this point I want to get it out of there - I could switch out the MPS myself. I am wondering if anyone else has had this specific problem of stalling, and if anyone knows someone in the Buffalo area who knows these systems. There was one guy at the BMW dealer here who replaced all my fuel lines before he retired about a decade ago, he was the last guy there who knew the D and L-Tronic systems.

Thanks

J-M

 

[sfdon]

If the MPS is disconnected the car will not run.
If it is defective it will run badly.

Why not install a known working MPS to solve your debate? Takes two minutes.

All of the Csi wearable parts are now available on loan from the e9 coupe Csi loan library.

I have to say that your fault description doesn’t sound like anything related to the MPS. More likely spark related?

 

[J-M Reed]

Thank you - I would like to try putting in a known working one. I did put in new spark plugs and wires, but I'm not sure if there is anything else related to that that I should look into. I was going to replace the cap / rotor but the mechanic said they were fine and did not need replacement. I also know he did not replace the cold start injector, because he said it started great cold. Anyway, I should have been on here a long time ago ...

 

[sfdon]

I would do simple cheap things first.
Swap out the MPS and start car. Wait 30 seconds and disconnect the plug from cold start injector and put vise grips on fuel line going to cold start injector.

If it still stalls out you know it’s not the cold start circuit or the MPS.

 

[J-M Reed]

Thank you. Who do I contact for the lending library?

 

[sfdon]

I’m going with spark still….
Check your dropping resistor for voltage to the coil after startup.

Did you check your trigger points for fuel injectors inside the distributor?

 

[sfdon]

Me- I’m the librarian!

 

[Stevehose]

It starts and runs beautifully now until it gets to temperature and then stalls out.

Swap an ignition coil to confirm it's not this?

 

[J-M Reed]

I’m going with spark still….
Check your dropping resistor for voltage to the coil after startup.

Did you check your trigger points for fuel injectors inside the distributor?

No I did not. I will have that checked

 

[carl westcott]

I am looking for help with my fuel injection system. I have a Euro 1973 CSi and I've had it in a shop for several years now - mostly sitting there with the hood up and no one doing anything. Anyway - it went in for no wipers and window motors not working. Now those work but, of course when it was started (with gas drained and replaced) the fuel injectors all started leaking. Those were replaced along with plugs and wires as 2 wires were arcing. It starts and runs beautifully now until it gets to temperature and then stalls out. The mechanic did a smoke test to check for vacuum leaks, none, and he also replaced the thermostat and tested the temperate sensor (good he says). He also did a compression test and I have great compression. I read the online article (found through here) by Paul Anders on the Manifold Pressure Sensor and sent that to the mechanic. The thing I did notice about my MPS is that prior to my ownership the epoxy was drilled out. I have tried to find anyone in my area (Buffalo, NY) who knows the D-Tronic system to no avail. At this point, the mechanic and I have been in several arguments, with him adjusting the tuning to keep it running - which worked for a couple days, and him saying it may or may not be the MPS. At this point I want to get it out of there - I could switch out the MPS myself. I am wondering if anyone else has had this specific problem of stalling, and if anyone knows someone in the Buffalo area who knows these systems. There was one guy at the BMW dealer here who replaced all my fuel lines before he retired about a decade ago, he was the last guy there who knew the D and L-Tronic systems.

Thanks

J-M

The extra air valve for cold start may be stuck open. Clamp the hose from it to the intake manifold when car is near warm. Or remove the hose and plug the hole on the intake manifold.

 

[carl westcott]

 

[carl westcott]

This valve and hose.

 

[J-M Reed]

Thanks everyone - I had a good talk with my mechanic and he was very happy I got on here. I am sending him what everyone has said and he will try these things. He did clarify that he starts the car and lets it idle, and it runs great until it gets to temperature and then the idle goes up and down until it stalls. He will report back after he tries some of this.

 

[sfdon]

The AAV being stuck open will not make your engine die.

 

[tochi]

I am looking for help with my fuel injection system.
the fuel injectors all started leaking.
Those were replaced along with plugs and wires as 2 wires were arcing.
It starts and runs beautifully now until it gets to temperature and then stalls out.
The thing I did notice about my MPS is that prior to my ownership the epoxy was drilled out.

Random thoughts.

The fact that the Pressure sending unit had altered epoxy plug does not necessarily indicate that the unit is bad. The epoxy is an obvious deterrent from tampering with a critical adjustment, but quite possibly, yours was tweaked by someone familiar with such an adjustment. Conversely, someone may have suspected that the pressure sending unit was faulty and attempted to determine whether it was fixable.

You state that the vehicle starts and runs - until it reaches normal operating temperature. This can indicate a lot of things other than the pressure sending unit. For example, your vehicle has a cold start injector/valve that functions in tandem with the auxiliary air valve. “IF” the temperature-sensitive air valve closes as the vehicle reaches operating temperature, AND the cold start injector fails to shut off or “leaks” this might result in an over rich mixture causing the engine to flood, run poorly or even stall. Since the fuel system is under significant pressure, a leak may be far more than an occasional drip. When the engine “stalls out” are the spark plugs wet? “Some” who have experienced this problem have plugged the fuel supply hose to the cold start valve, thereby depriving it of fuel while not introducing any unwanted vacuum issues.

"IF" your fuel pressure is low/minimal (due to numerous causes, including a malfunctioning fuel pressure regulator) your cold engine could be operating “beautifully” caused by the extra fuel supplied by the cold start system, along with the additional air from the "cold" auxiliary air valve. When the engine reaches normal operating temperature AND the cold start system ceases to supply “extra fuel,” low fuel pressure could be responsible for poor operation and, as you describe it, “stall out.”

The "simple" D-Jet system is also controlled by temperature sensors. These sensors can also affect the air-fuel mixture. According to one source, when disconnected, the air temp sensor found in the intake manifold can reportedly enrich the fuel mixture by 20%. The engine temperature sensor reportedly can impact the fuel mixture by an even greater degree. Are the sensors properly connected to the wiring harness?

Since your symptom is reportedly temperature sensitive, one wonders if you might not have a weak ignition coil or a malfunctioning ballast resistor that feeds voltage to the coil. You do not mention how long it takes for your vehicle’s engine to reach “stalling” temperature. Is it five minutes or much longer? In theory, when the ballast resistor is cold and not resisting, the coil is fed a full 12 volts. When the resistor is hot, it limits voltage to the coil to protect the coil from overheating and lengthen its life. A marginal ignition coil or a coil that is starved for voltage may be inadequate to handle your spark plug voltage requirements, causing a stall situation.

https://e9coupe.com/forum/threads/d-jetronic-rebuild.18687/
https://e9coupe.com/forum/threads/smokin-hot-ballast-resistor.9504/

Gratuitous distractions

 

[J-M Reed]

Very nice distractions....

I did just go down and go over all this with my mechanic. He was thinking about when this all started.

He says it really started when he put the new thermostat in. The old one was stuck open so he replaced it. Now, the car starts great and it will run until the car gets to operating temperature, about 1/2 way up the gauge. Then the car starts oscillating - the idle goes up and down until it finally can't recover from the low and stalls. he does not think it is the coil.

 

[sfdon]

Block off the Cold start injector hose and pull the connector to the injector.

 

[sfdon]

What idle when cold start?

 

[day66]

Water temperature sensor problem?

 

[sfdon]

I find the cold start system and the trigger points are big issues for running rich.
Default for bad Fuel Pressure Regulator is also rich.

Need to disco cold start system and check fuel pressure.