The gas mileage I'm getting seems to be below what I see others are getting at around 10 mpg. The car seems to be running fine in all respects so I'm planning on replacing the oxygen sensors before I explore the rest. The car has about 63k on the clock and I've put about 3 of that on myself.

Any words of wisdom before I begin are appreciated.

 

If you have a voltmeter you can check the sensors.

If you decide to replace them I suggest springing a few extra bucks for the one with the proper connectors as opposed to the cut-n-splice type. Not essential, though.

As for some other things that might cause poor fuel economy....

-fuel enrichment switches stuck "on"
-seized advance mechanism in distributor
-distributor vacuum advance unit inoperative
-coolant temp sensor skewed and/or faulty connector plug

Cheers
DD

 

Also don't forget to use some anti seize, it may be provided

 

Thanks for the advice. I appreciate it. It will be a few days until I get to work on it, but I will let you know how it goes. These cats take work and patience, but I grin every time I go into the garage!

 

Just replaced the upstream OS today because the check eng light was on for a couple months. I use Walker OS. Never heard of the brand but they are cheap and direct plug-in (no wire cutting needed). I paid $56 each on Amazon. I am going to clear the CEL code tomorrow and see how it goes.

 

So here's where I am:

Needed new tires so while it was in with a British mechanic I had the sensors checked and they are fine. He said the carbon emissions were high and gave me some 44k additive to see if helps clear the injectors. I'm guessing an injector cleaning may be needed even if this helps some.

Next step and something unexpected - I ordered a new distributor vacuum advance. The one in place wasn't original but given age, heat etc. it seemed worth it for the price. While waiting for the part I got caught in a serious downpour and the passenger bank developed a putt, putt, putt. Opened the hood, pulled the cap and figured I'd let it dry while I waited for the parts.

Part came, slowly took things apart, cleaned as I went along and the new advance went in fine. Put everything back together and... now I have a put, put, put on both banks. No backfiring, smoke etc. The tach also takes takes a few seconds to register.

Connections seem to be fine and vacuum lines appear to be connected. Any input is appreciated. Thanks

 

44K is a good product but you're right....you might still need a professional injector cleaning.






Was the inside of the cap wet, or were you assuming it was wet? Given its location it would be pretty hard for the distibutor to get soaked, IMHO, but, anyhow, if it DID get wet, air drying may not have been enough. FWIW, if I have a wet cap I give the WD40 treatment and then aerosol brake wash and let it sit in the sun.






The tach reads off of the igntion amp so that might be a clue. Carefully check the wiring at the amp....it's easily damaged, especially the shielded wire.

If the plug wires of old they can be easily damaged as well, as can the fuel injection wiring. Almost any activity in that area can cause a problem with the brittle wiring

I'd go back and make sure the inside of the cap really IS dry and carefully inspect for any damaged wiring.

Did you change plugs at the same time?

Cheers
DD

 

I did not see any water in the cap/distributor and the cap was off with the hood open in the garage for several days. It was a guess that these components got wet. Is there something else that could have been impacted by moisture?

Plug wires are newish and no arcing was seen in a dark garage. I did not replace the plugs. I tried to remove one plug but it was extremely tight. I was using a socket with an extension and didn't feel comfortable with the angle. Any advice on tools and technique? The wrench in the tool set in the boot didn't fit over the plug.

I will go back and check the wiring at the amp. I do know that a short section of the connection is uncovered (bare wire) and that didn't seem right to me. It was however running fine previously.

Still enjoying the process despite it all. Crazy engine but it is becoming more clear a bit at a time.

Thanks for your advice. I really appreciate it.

 

Plug wrench that came with car doesn't fit on plugs? I would verify that the plugs are the right ones first. Also remember to gap them and NOT at .035. .

 

The plugs are too tall. Apparently not uncommon.

 

I think we may be on to something with the ignition amp. The wire connection facing the firewall was loose. I pushed it in and started the car and the driver's side bank no longer missed. The tach still took a moment to register before going to 1200 rpm for about 30 seconds. Then engine then started swinging between 750 and 1500 for a bit. I shut it down after that. The amp is a Lucas and the wire being right against the vee doesn't exactly look new.

I am also hearing a chattering from what I am pretty sure is the distributor. I heard it before I changed out the vacuum advance but had not remembered.

So... New amp and wiring sounds like it's next. Take another look at the distributor and this time while I'm at it (hey why not? ) I'll change the plugs. Any good way to get them loose? I'm guessing there wasn't any anti-seize used.

Thanks again.

 

Good the check and repiar any flakey wiring you find.

The principal component in the Lucas amp is an AC Delco D1906 ignition module....known to give problems with age and heat. Easy to replace but you'll need some tiny sockets to open the amplifier case. A problem with the amp wouldn't effect just one bank, though.

Pay particular attention to the injector wiring and connectors

My only luck with stuck plugs is a bigger breaker bar. Removing the throttle tower, dist cap, etc will make it easy to get a somewhat stright shot at them

If you really wanna go whole hog you'll pull everything out of "the vee", repair or make a new F.I. harness, repair all the wires and vacuum hoses, new spark plugs, new injector hoses, etc. Get it all done at once.


Cheers
DD

 

I'm going to dive in. There are enough parts of questionable age/status that it will be good to have them up to date.

For what it's worth, the distributor vacuum advance that I removed was not functioning, so I'm glad I replaced it. (and got experience getting to it.)

I follow directions found here Replacing the Vacuum Advance. The only point of note is that the locating pin he mentions does not punch through on the unit I replaced or the one I got to replace it. Fortunately it didn't look right to me and I felt for a hole on the bottom of the unit.

Wish me luck! I'll be back with questions, I'm sure.

 

It's a rewarding project and you get SO much done at once versus duplication of labor if the tasks are done individually. If you work slowly and thoughtfully it's actually sorta relaxing :-)

Take pics and LOTS of notes as to where all the vacuum hoses, etc go.

Cheers
DD

 

My connector facing the firewall was cooked pretty good too. Was able to find something that fit, with a small shave, at GM parts. The guy found something in the "miscellaneous" box LOL.

 

Doug I have a 90 V12 Marrelli: I'm not too happy with my mileage either; how do you check the voltage to confirm the O2 sensors are working? I'm too lazy to check every page and thread to find the info (210 pages now...I found this old thread). Im guessing you check when cold and hot. Do I need to make a special pigtail to be able to probe for a voltage check? Thanks in advance.