S52 MPG/Economy Gauge Issues

[Klug]

Hey M52/S52 guys-

What are you typically seeing on your MPG/Fuel Economy gauge on your swaps? I am having an issue where when under throttle, the MPG works as it should- but when I back off- the needle throws itself all over the place- so much it broke the needle off of the cluster after a few hours of driving. The car runs great, no vac leaks nor codes and all the other gauges work all to spec.

I swapped in another cluster and I'm seeing the same issues. Ground nuts and all that typical cluster troubleshooting has been verified, cleaned and checked.

I get good conductivity from the X20 to the C101 and then to the cluster. With MS41.1 DME I have X6000 Pin 9>X20 Pin 24>C101 Pin 8>Cluster.

I am aware this output to the cluster is determined from vac pressure. I've smoke tested the engine prior and I can assure you I'm not having any vac leaks. I have a KAMotors CAI intake, but I can't really see that being an issue since my M20 has one too and don't have an issue there.

Just curious if anyone else had this issue before. Thanks guys-

[BlackSpeed66]

I believe the issue has to do with the injector pulses that the OBC reads. It is different from the m20 and the later model engine, thus both the econo meter and OBC display crazy readings. 'Hoveringuy" on r3v here makes a small add-on circuit which is adjustable to correct this issue so the OBC sees the correct pulse. I believe his website is www.seattlecircuit.com.

I picked one up about a year ago - finally hoping to install it this winter since I've got some other stuff worked out now. Its funny to see i have '6XX' miles when i top off the tank on the 'range' function on the OBC. Too bad it's not true!

[2mAn]

Ive always wanted to get this fixed on my swap... maybe in 2017

[Klug]

Is it really tied into the OBC? I honestly thought the DME tells the cluster the MPG and not through the OBC...but thinking about it now...I guess they are all tied in together.

2mAn- Do you have yours still connected? I'm tired of breaking needles. When I mean it throws itself back and forth- it literally THROWS itself from zero to 40 and all over. I might just disconnect it as I don't want to break any more needles and commandeer more clusters I have laying around.

[Varinn]

That doesn't sound right. I have an s52 in mine and the econo gauge reads just like stock, but incorrectly. Example; mine will show around 6L/100km when reality is 12L/100km. Aside from being scaled wrong it behaves normally. I'd say you've got something else going on.

[2mAn]

2mAn- Do you have yours still connected? I'm tired of breaking needles. When I mean it throws itself back and forth- it literally THROWS itself from zero to 40 and all over. I might just disconnect it as I don't want to break any more needles and commandeer more clusters I have laying around.

Mines limp, doesnt move . I also have no OBC on my car because its an 84 that only had a clock, no check panel. Im also on OBD1 so its not exactly the same wiring, though the pin on the X20 might still be the same.

[Klug]

That doesn't sound right. I have an s52 in mine and the econo gauge reads just like stock, but incorrectly. Example; mine will show around 6L/100km when reality is 12L/100km. Aside from being scaled wrong it behaves normally. I'd say you've got something else going on.

Do you have a 13 button OBC also? I know the coding plugs on them are dependent on the engine- along with the coding plug on the cluster itself.