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Vintage Bosch d-Jet running rich

shaned

Member
Joined
Nov 3, 2014
Location
Kansas City, MO
Hello<
I am finally getting my 1973 Volvo running reliably, but I am still running rich. I am using a 195 degree Stant thermostat, but i am not convinced it is the best one to use in my application. I have heard this can be a common cause of overfueling, but I am open to suggestions?

"This is a list of items replaced or mended" just to save time
New injectors+Seals
Cleaned and tested Aux Air Valve, and new hoses
Replaced MPS with a known functional one
NOS TPS adjusted
Fuel pressure regulator adjusted to 30 psi
123 dizzy
New coil+plugs
New ambient and Coolant Temp Sensor
(plugs fowled with under 100 miles on them)

Thanks!
 
Get a multimeter and make sure the coolant and air temp sensor readings are correct. Easiest to check at the sensor, but if that's good, still worth checking at the ECU to make sure it's not a harness issue.

Maybe double check that the cold start valve isn't causing it - go ahead and unplug it.
 
What's the part # on the MPS? '73 should have a 0 280 100 054.

How do you know it's functional? Does it hold vacuum?

Has the end cap been drilled so it can be adjusted?
 
Thanks, JohnMc i will check the cold start. i didn't think of that.

As for the MPS. I purchased it from a Volvo shop owner named Frank Ponte. He had a shop that he was closing. He seems like a straight shooter. He stated that it came off a functional car, and yes, the wax was still on the adjustment screw. We matched the number to the one on my car. (the one you listed) It is possible it is worn, but does function vastly better than the one it replaced.

So I assume we don't think the thermostat is the issue then. What is a good operational temp for these cars?
 
You should still do a vacuum test on the MPS(VPS) to see if it holds. If the diaphragm inside the vacuum sensor is broken, it will cause a lower vacuum reading to the ECU which in turns causes a richer mixture.

FYI, I am almost 100% sure that you won't find a suitable thermostat in any of major auto parts suppliers like Autozone, Oreillys or Pep Boys.

Napa might be might have 1, but I get mine from wholesale suppliers of European car parts. I will only use thermostats made by Wahler, Vernet and Calorstat, all made in the EU in my customers red block Volvos as they are the correct size and have the proper sized disc on the bottom of the thermostat.
 
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Update: I used an NOS Wahler I found in my stash, cleaned the plugs, and it seems much better. I will pull the plugs after a few trips to see if we are moving in the right direction.

(Planetman)I heard you can damage the MPS with that test? You are probably correct in that being the issue. I had recently replaced the wiring for the coolant sensor and tested it @ the ECU. :), so I am confident in that. You guys are serious trouble shooting bloodhounds! thx!
 
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