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  #1  
Old 09-17-2019, 02:47 PM
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Join Date: Mar 2011
Location: Victoria Canada
Posts: 37
'94 E320 124.032 high fuel consumption question

Canadian car, 300K kms approx.

Recent fuel consumption around 12.5 MPG (18 litres per 100 km). Replaced 02 sensor after finding blink codes 11,13 on Socket 8. Replaced fuel pressure regulator on fuel rail because I though i could smell gas in there. Fixed a post CAT exhaust leak.

If anything, fuel consumption is worse! I'm unable to retrieve codes on Socket 3, which looks like the next place to go. When I hook up my home-brew reader, I get a steady light. Looks like Socket 3 is fully or partially grounded already.

This car has the 16 socket interface. It also has an on-board button and LED for the DM Socket 3, but this does not appear to work. May be related to the short to ground?

Any ideas for the fuel consumption or how to get codes out of Socket 3?

++++++++++++++
Additional:
Wiring harness replaced by PO some years ago; have receipt
Throttle body recently replaced with a newer unit (2006?)
Have a bad OVP and waiting on a part shipped from US
Constant ABS light, due to bad OVP, probably
Brakes checked for dragging
Car otherwise runs well, idles smooth, holds steady at 80-85 C, good power, minimal oil leaks.

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  #2  
Old 09-18-2019, 01:44 PM
I told you so!
 
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Are you pressing the button on the built-in diagnostic module for 2-4 seconds?

Are you set up to read codes from Pin 8 and Pin 14?
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  #3  
Old 09-18-2019, 03:40 PM
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Location: los angeles
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Try the airmass meter ,test or swap one
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  #4  
Old 09-18-2019, 05:31 PM
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Id look at the coolant temp sensors if its running good. The air mass would make it run rough. Ecu probably thinks the engine is cold all the time and dumping gas in.
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  #5  
Old 09-18-2019, 06:37 PM
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Location: Victoria Canada
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I am reading the socket 8 and 14 codes from a home-brew blink reader. Pressing the on-board button in position 2 does nothing, no light, no blink, no action. And trying to read DM codes directly through socket 3 I get a constant bright light on the blink reader as soon as I hook up (ie, don't need to ground the socket to pull current).

Quote:
Originally Posted by Kestas View Post
Are you pressing the button on the built-in diagnostic module for 2-4 seconds?

Are you set up to read codes from Pin 8 and Pin 14?
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  #6  
Old 09-18-2019, 06:44 PM
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Good point. I just realized that there are two senders on this car, one for the dash gauge (which appears to be working) and another one for the ECU. Perhaps that one is not working! That would give the 'open loop' diagnosis some merit.

Probably it is easier to just replace it rather than try to diagnose.

If I had access to socket 3 codes it might show up. Nothing showing yet on Socket 8 (where code 2 is temp sensor).

Thanks for the suggestion.

Quote:
Originally Posted by speednjay View Post
Id look at the coolant temp sensors if its running good. The air mass would make it run rough. Ecu probably thinks the engine is cold all the time and dumping gas in.
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  #7  
Old 09-18-2019, 09:49 PM
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Location: los angeles
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Disconnect diagnostic module and then reconnect , ive seen a few do this and after rebooting it reads codes , its under the dash
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  #8  
Old 09-23-2019, 10:47 PM
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Location: Irvington, N.Y.
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On high fuel consumption, any gas car, first pull the air mass filter and tell us what happens.
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  #9  
Old 09-28-2019, 01:35 PM
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Thanks to John and others for some great ideas/suggestions. The car is currently with my daughter in another city, so it will be a couple of weeks at least before I can look into any of this. Will keep the thread alive and if it gets sorted, make sure the solution is recorded.


Quote:
Originally Posted by John Carroll View Post
On high fuel consumption, any gas car, first pull the air mass filter and tell us what happens.
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  #10  
Old 10-20-2019, 05:58 PM
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I got some time with the car and followed the suggestions. I'll put the results into the first post to be more useful for others with this same problem.

I also swapped in a new OVP relay and the ABS light went out. Hurray!

OK, the Edit option on my first post has timed out so I'll have to report here.

Faulty coolant temp sensor (Post #4): Ordered a new one and installed. Checked the old against the new in a water bath. This is essentially a switch. It is open until about 115-120F and then closes with a slight resistance. The resistance drops as the switch warms up so perhaps this is also used by the ECU. Here are numbers for the new sensor 60-115F open; 120F 1.9 ohms, 130F 1.7 ohms; . . . and so on . . . until 150F 1.1 ohms. The switch I pulled out had a '93 build date on it (original) and matched all the above numbers within a small margin of error. Conclusion: I don't think the temp sender is the problem.

No diagnostics from Socket 3. (Post #7): This is a Canadian car and it has the California setup with the diagnostic module (DM) under the steering column and a button on the socket cluster to read without a blink code reader. I pulled and reset the DM multiple times, cleaned the pins and nothing changed. By the way, getting the DM out is a slight puzzle. There is a dial on the front. Turning the dial from I to O moves the DM away from the contact pins. To get it out from that position, you have to lift (or depress, can't remember) lock tabs on each side near the back side of the DM. It then comes out easily. You do not need to remove the mounting bracket with the DM! Anyway, I checked Socket 3 with the DM out and there was no longer short to ground. Put the module back in and the short reappeared. The car runs the same with the DM in or out. Conclusion: Looks like the DM is bad, and not the wiring. I've sourced a used one and will swap it in next time I have access to the car. It would be nice to be able to read the codes from Socket 3, but that will have to wait. If these are indeed just for diagnostics and the DM does not feed any info back to the ECM, then probably it is not the cause of my problem.

MAF bad (Post #8) I connected and disconnected the MAF cable and there was no discernible change at idle. I fiddled mightily with the cable while plugged in to make sure there was no intermittent connection problem. I pulled the MAF and cleaned it (did this last December but why not?). No change either plugged in or disconnected. What I didn't do, and I'm kind of mad that I didn't, was to disconnect the MAF and drive around a bit. I only monitored idle. Conclusion: I may have a bad MAF module but then why does the car run so well?? Not super eager to buy a used one on the web, and new ones are a little pricy, but this seems like the next step.

I don't expect the problem has been fixed, unless by some miracle the OVP relay was messing things up. My daughter is running a mileage check and will report back. In the meantime I may visit my independent and see if they have a known good MAF module.


Quote:
Originally Posted by birkhoff View Post
Thanks to John and others for some great ideas/suggestions. The car is currently with my daughter in another city, so it will be a couple of weeks at least before I can look into any of this. Will keep the thread alive and if it gets sorted, make sure the solution is recorded.

Last edited by birkhoff; 10-20-2019 at 06:33 PM.
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  #11  
Old 10-23-2019, 01:34 AM
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Location: Victoria Canada
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Mileage report: 13.82 litres per 100 km or ~17 mpg US city driving, no aircon.

That's much better! Still, I understand this car should do 23-25 mpg city with a light foot. I'll do the MAF and install the CARB module and see what happens.
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  #12  
Old 10-23-2019, 06:15 AM
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feel your rims near center,after a drive,for heat.Brakes can bind and cause mileage to go south
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  #13  
Old 10-23-2019, 10:51 AM
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Quote:
Originally Posted by birkhoff View Post
Still, I understand this car should do 23-25 mpg city with a light foot.
Who told you that? I'd be surprised if you could get that with highway MPG's. You have a heavy car, a slush box with a 1:1 final gear ratio (no overdrive), and no lockup torque converter (you're slipping ALL the time). Maybe with a manual and hypermiling techniques you could do 23-25 city, but auto? Maybe downhill with a tailwind...
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  #14  
Old 10-24-2019, 05:03 PM
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It's mentioned in the first post. It's not the brakes.

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Originally Posted by oldsinner111 View Post
feel your rims near center,after a drive,for heat.Brakes can bind and cause mileage to go south
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  #15  
Old 10-24-2019, 05:09 PM
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Quote:
Originally Posted by Diseasel300 View Post
Who told you that? I'd be surprised if you could get that with highway MPG's. You have a heavy car, a slush box with a 1:1 final gear ratio (no overdrive), and no lockup torque converter (you're slipping ALL the time). Maybe with a manual and hypermiling techniques you could do 23-25 city, but auto? Maybe downhill with a tailwind...
I got it by a search on this forum! Admittedly a wide range of reports ranging from low teens like mine (obviously something wrong) to nearly 30 if I recall (that one probably user error). The official EPA numbers are around 22 combined. But I take your point. Kicking around 3500 lbs of iron, rubber and glass has got to cost something . . .

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