Lean running, my 1976 2.0 FI engine

Ron Avery

Ron Avery

True Classic
As some of you may know, my Montecarlo as been in the shop since last July. On my way from Oxnard Ca. To the Lancia event up north, I discovered that the car was running very lean. I made it up to The Monterey are. And had to turn around and go home. The engine temp did not reflect how hot the exhaust system had become ( the temp gauge was normal). When we got up to Monterey, I discovered that the paint on my rear bumper had blistered. I checked the plugs and they looked white. As most of you may know my Montecarlo has 2.0 with Bosch L jet injection, had been running good for years. Even before I purchased the car in 2022. The FI system does not allow much if not any adjustability. When I arrived home I took the car to my shop. They had an exhaust analyzer read the air fuel ratio. It was very lean, and confirmed my suspicions. They were quite busy so it sat for a while. We looked over the exhaust system after I pulled the bumper for a repaint. It turns out that two of the header tube had cracked near the flange. And the exhaust pipes on either end of the muffler had also cracked. I had the header re welded and head coated. The rest of the exhaust system was also repaired. We then set about replacing a lot of the fuel supply system. New injectors, new coolant temp sensor, new fuel filter, new fuel pressure regulator. We checked the Mass airflow meter ,It was not dirty and the flap moved freely. We also replaced the wiring harness to the mass airflow meter .We did find that the rubber air intake hose for the Mass air flow meter, had deteriorated, and had some cracks. So a suitable replacement part.was found. I also replaced.the thermostat. I also had the color start valve replaced. The photo of the spark plug is from after the repair work.
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We did burp the cooling system, we then ran the car, it was still lean, not has lean. But more than we liked. The ignition timing was checked and found to be at spec.
My shop then drilled out the plug in the Mass Aiflow meter to adjust the air intake screw. As per the Bosch shop manual. This did the trick. The next visit to the Analyzer showed we were within spec with the reading..We also performed a leak down test on the engine, to see if it had any damage . It was well within Normal parameters . What a relief! I forgot to mention that we did add heat, shielding material above the exhaust system, and on the backside of the bumper.image000000 2.jpeg
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Ron Avery said:
As some of you may know, my Montecarlo as been in the shop since last July. On my way from Oxnard Ca. To the Lancia event up north, I discovered that the car was running very lean. I made it up to The Monterey are. And had to turn around and go home. The engine temp did not reflect how hot the exhaust system had become ( the temp gauge was normal). When we got up to Monterey, I discovered that the paint on my rear bumper had blistered. I checked the plugs and they looked white. As most of you may know my Montecarlo has 2.0 with Bosch L jet injection, had been running good for years. Even before I purchased the car in 2022. The FI system does not allow much if not any adjustability. When I arrived home I took the car to my shop. They had an exhaust analyzer read the air fuel ratio. It was very lean, and confirmed my suspicions. They were quite busy so it sat for a while. We looked over the exhaust system after I pulled the bumper for a repaint. It turns out that two of the header tube had cracked near the flange. And the exhaust pipes on either end of the muffler had also cracked. I had the header re welded and head coated. The rest of the exhaust system was also repaired. We then set about replacing a lot of the fuel supply system. New injectors, new coolant temp sensor, new fuel filter, new fuel pressure regulator. We checked the Mass airflow meter ,It was not dirty and the flap moved freely. We also replaced the wiring harness to the mass airflow meter .We did find that the rubber air intake hose for the Mass air flow meter, had deteriorated, and had some cracks. So a suitable replacement part.was found. I also replaced.the thermostat. I also had the color start valve replaced. The photo of the spark plug is from after the repair work.View attachment 81644View attachment 81645We did burp the cooling system, we then ran the car, it was still lean, not has lean. But more than we liked. The ignition timing was checked and found to be at spec.
My shop then drilled out the plug in the Mass Aiflow meter to adjust the air intake screw. As per the Bosch shop manual. This did the trick. The next visit to the Analyzer showed we were within spec with the reading..We also performed a leak down test on the engine, to see if it had any damage . It was well within Normal parameters . What a relief!View attachment 81638View attachment 81639View attachment 81640View attachment 81641View attachment 81642View attachment 81643
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Those air intake boots are a problem. I wonder if any one has reproduced this item. I was about to buy a 1981 Lancia Beta that had a similar boot tear. No replacement boots were available then, 20+ years ago.
 
I see the bottom side plug out of your air flow meter. I have never taken that out. That would seem to be a huge vacuum leak, unless it was put back. You can also add some resistance to the coolant temp circuit of the EFI system to richen the mixture if all else fails. Works well and is a must if doing performance work. imho
 
BEEK said:
I see the bottom side plug out of your air flow meter. I have never taken that out. That would seem to be a huge vacuum leak, unless it was put back. You can also add some resistance to the coolant temp circuit of the EFI system to richen the mixture if all else fails. Works well and is a must if doing performance work. imho
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A new plug was installed, I will be adding an air/fuel gauge and the knob that will be connected to the temp sensor.
 
Ron Avery said:
A new plug was installed, I will be adding an air/fuel gauge and the knob that will be connected to the temp sensor.
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Air/fuel ratio at idle is only the beginning, more important is A/R at cruse running, under part load, at full load. The fuel system must adjust the A/R as required by the motor. This where a data logger (A/R, engine rpm, operating conditions, exhaust temp per cylinder) can be very useful to help figure this out.

Keep in mind a single O2 sensor the exhaust is a sum of all cylinders, does not indicate a single cylinder with a problem. Or why proper testing requires one wide band O2 sensor per cylinder combined with data logging as a start.

Consider making a replacement intake plenum hose with silicon hose, bends and band clamps. Properly done this could produce a better and more durable hose than oem.


Bernice
 
Wouldn't an infrared thermometer pointed at each exhaust runner indicate one was running leaner (hotter) than the others if that in fact was the problem? Seems you found a lot of issues with the intake hose, even the spider and X hoses had the same failure mode.
 
All the plugs were the same very light gray /white. When the problem started. So I it was an overall problem.
 
carl said:
Wouldn't an infrared thermometer pointed at each exhaust runner indicate one was running leaner (hotter) than the others if that in fact was the problem? Seems you found a lot of issues with the intake hose, even the spider and X hoses had the same failure mode.
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Might be ok when the motor is idle going no where.. The important exhaust temperature numbers is under load moving.. This could be an issue with using a hand held IR thermometer.

BTW, small aircraft powered by piston engine(s) have exhaust temp gauge on the panel and A/R mixture adjustment near by.


Bernice
 
While the other parts replacements probably couldn't hurt, IMO the 800lb gorilla in you photo album was the deteriorated intake hose. All manner of false air being let in that the FI system could not account for, causing your crazy-lean situation.

It's a missed opportunity that while your header was out being repaired and recoated, a bung was not welded in to accommodate a wide band O2 sensor to drive an Air Fuel Ratio gauge that could be either permanently installed or rigged up for periodic installation as desired or needed. As pointed out by Bernice, one sensor does not give you the granularity of a sensor monitoring each cylinder, but for a non-race, hobbyist/enthusiast application, should be just fine.
 
I was going post and update iin an a month or so, once it was installed. I have a gauge ready to install. With an adjustment knob (in place of the cigarette lighter), that will be wired into the coolant temp sensor for the Fuel injection. There is already a place for a sensor in the header, ready to go. My shop is moving there location. So I will take it back in a month or so for the insulation
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Ok I finally had my car on the DYNO at Ed Pinks Racing in Van Nuys Ca. I have my air fuel ratio gauge installed along with my fuel enrichment knob that is wired into the temperature sensor for the coolant in conjunction with the fuel injection system.. at this time however, the air fuel ratio gauge is not working because I have to get a new O2 sending unit. itiwon’t calibrate so on the air fuel ratio knob we have made two dots one is it 1 o’clock and that’s for starting the car, the other dot is roughly at 5 o’clock which is for performance driving anywhere in between is for cruising. The car basically has just under 130 hp at the crank at 7200 RPMs. With an air fuel ratio reading of. 13.4. The technician thought this was the best compromise for the system, and as you can see, the power does not drop off it just simply levels out at that RPM.
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Noted on the dyno curves,
torque peak @ 5500 RPM 108lb/ft
hp peak @ 7000 RPM 125hp

This means optimum shift point is 7500/7800RPM due to area under the curve.
Running A/F of 13.4 is good trade off for power.

BTW, The Lampredi TC is capable of producing a LOT more power than this.

Bernice
 
Thanks for the results.
I think that he input only 12% driveline losses, is too optimistic!
 
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