79 Eldorado 350 EFI Running Lean at 15 MPG

Started by Jaks79Britz, June 21, 2022, 07:48:05 PM

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Jaks79Britz

Almost there! I know it's been a few months, but I thought it would be good to give an update on my 79 Biarritz lean condition.  I sent by ECU to Bruce Roe to get tested and it turned out it was running good, but about 15% too rich. Having had that tested, I was able to re-focus on items that would cause the high NO levels.  I replaced the CAT, tested and cleaned the EGR valve, and had the smog pump rebuilt.

On the latest smog test, all emission levels came down and all passed except for NO at 15 mph.  As you can see below, at 25 mpg the measurement came in well below AVG and MAX.

Why would levels at 15 mph be so much higher than at 25 mpg?
 
Also, today I found out today that I have an exhaust manifold leak on the passenger side.  Could this be the final piece to fix?  I don't want to mess around with too much and then regress my progress
79 Eldorado Biarritz
79 Coupe Deville

Dave Shepherd

If you mean nox,high cylinder temps cause this, it is the function of a correctly operating  egr system to cool the cylinders. A lean condition,or improper timing are some of the common issues that can cause this, the egr valve may be ok, but if the exhaust passage is restricted  to the egr, that would definitely  cause high nox.

V63

You can remove the EGR and start the car (It's going to be loud) and rev it a bit you should see chunks of carbon blowing  out

Jaks79Britz

It has to be the EGR.  I've checked the vacuum line and have done the EGR test according to service manual. It's the original EGR and appears to be working, but I've ordered a new to see if I get a different result. I'll try idling without the EGR installed to see if that helps too. 

79 Eldorado Biarritz
79 Coupe Deville

bcroe

Make sure the EGR passages in the manifold are clear, most I check are completely plugged. They were mostly created with a long drill, I clear them the same way.  Bruce Roe

Jaks79Britz

Quote from: bcroe on June 22, 2022, 11:53:34 AMMake sure the EGR passages in the manifold are clear, most I check are completely plugged. They were mostly created with a long drill, I clear them the same way.  Bruce Roe

Thanks Bruce.  I cleaned the passages with compressed air, but didn't think to get inside with a long drill.  I'll try that and report back. 
79 Eldorado Biarritz
79 Coupe Deville

bcroe

A couple other things come to mind.  The OEM timing
chain set for these cars fails of old age, even at
lower miles.  Slack the cam can bounce forward and
back, generally emissions go down with retarded spark. 

And then there is the ESS, see if it is working and
giving propoer spark timing. 

If an engine is not stressed much, there is more
tendency for carbon buildup in cylinders.  Sometimes
removed by running some water mist through the engine. 
good luck, Bruce Roe