Cynthia --

It's not unreasonable to expect low to mid 20's with that car, depending on variables. I had a '72 142EA (automatic) that would regularly get 20-23 around town and 24-27 on the highway...

Four things are known to commonly cause this kind of trouble with D-jet:
-- A failing MAP sensor
-- A failing engine temperature sensor or bad connections to it, raising the circuit resistance. (In fact, this was a trick to richen the mixture for folks who modified their motors.)
-- A bad or leaking cold start injector (or one of the main injectors, for that matter...)
-- Mis-adjusted fuel pressure (should be set to 28 psi).

I'm sure you've already confirmed engine timing.
--
Don Foster (near Cape Cod, MA)

Just for comparison:
My 71 142E gets EXACTLY 27.5 mpg on my daily commute. This average is based upon a daily 52 mile trip, of which half of it is on a 65-70 mph freeway and half is on a 55-60 mph country highway with some smooth hills and a 4 mile 35 mph zone.

This is in Overdrive almost the entire time(95%).

My fuel gauge does not work so I have extensive detailed records of fuel usage. Also, my wife says I am an asshole when it comes to paperwork and documentation. With this, use this information as you see fit.



Later,
Jeremy

I'm in the same boat with no fuel gauge plus no odometer. When the odo worked I got 18-21mpg depending on enthusiasm & temp. You might want to check the fuel pressure in add. to general tune up stuff. Check the thermostat[I use a 195 degree in the winter & 160 in summer-makes a big difference]. Happy trails!

Mike M.

While D-jet can suffer from the occasional mechanical malady, much of it troubles are electrical in nature - having a wiring loom with small wires survive 30+ years next to a hot engine with no problems is pretty difficult.

Before embrarking on any FI system tuning or checking, just go over a few other basics first to make sure they aren't causing problems. Adjust the valves. Adjust the point gap and set the timing. Possibly check the compression (or just pull the coil wire and crank it round and round to ensure that all four cylinders are at least roughly equal in the amount they slow the starter motor).

Then on to the FI system. There are plenty of links on the 'net dealing wth the D-Jet system - as it was used on a fair number of cars. Here's a small list of links I found:

http://www.164club.org/volvlink.html#bosch

You need a multimeter and a FI system wiring diagram. The best practice (IMO) is to pull the main plug off the computer (it is under the passenger seat in a 140) and check the various readings there with a multimeter reading between the various proper terminals (consult that wiring diagram). That way in one fell swoop you test both the sensor and the wiring. If you find a problem (a reading out of the ordinary) then test again at the sensor itself to distinguish between the sensor or the wiring.

That being said I'd guess it is either a leaking cold start valve, injector, or a bad coolant temp sensor that is making yours run rich.

To test the cold start valve, just remove it from the manifold, leaving it attached to the hose. Then turn the ignition on several times, but don't crank. The fuel pump should run for a few seconds each time and build up the full 28 psi. Then check that no drips come out the cold start valve.

To check the injectors just pull off the entire fuel rail and injectors with all hoses and wires still attached. Just release all four sheet metal collars holding the injectors on, possibly give each injector a little slight twist to break it loose, then pull the whole mess out of the injector holder slightly - enough to expose the injector tips. Then turn the key on again several times, all without cranking. Check the injectors for drips. While a little bead or occasional drip might occur, what you don't want is a drip drip drip. But to be honest, unless it is -really- leaking the drips won't do much other than make it run slightly rich at idle, and won't have much affect on driving mixture. While you have the injectors out, you can also do a quick shade tree check on them. Turn the key on several times (without cranking) and leave it on. Go over and manually open the throttle - this should trigger the injectors in alternating pairs. Just visually check that each injector has a nice healthy spritz - no dribbles or sprays weaker than its siblings. Occasionally injectors that sit a little too long will stick shut - rather than shell out $100 for a new injector just try gently pushing that pin in the tip in - often that is enough to break the gum holding it shut - once it is working the gasoline can flow through and keep it clean.

As for the coolant temp sensor - find a link that has the graph showing the expected resistance per temperature, and test it both cold and warm. There is an air temp sensor as well - but its effect is barely noticable. The coolant temp sensor, however, will make your engine run very rich when it fails.

Tweaks like messing with the fuel pressure or MAP sensor tuning should be reserved for modified engines - on a stock engine you shouldn't need anything other than the proper settings. Using those adjustments to compensate for another failed component is not a good idea.

Yeah, that seems a bit low. But on the other hand, it also seems like what i average with my DGV equipped b20. For what it's worth... (but on the other hand, i drive pretty aggressively, and my DGV leaks around the throttle shaft).

Good luck
Kyle

I think that your mileage could be improved somewhat. Do you have the
M40 or M41 tranny? Some tuning and adjustment would probably help.
You should be getting at least 20 on the highway, fagunnessakes, I can
beat that in my gas guzzling 164!

A look at your spark plugs may help. Should be tan. If they are black,
the engine is running too rich. Keep track of which cylinder the plug came
from if they are different - could be an injector problem.
--
George Downs, Bartlesville, Oklahoma, Central US