Noob Scorpion Guy

Gee its been quiet on this forum. Where did everybody go?

Found this on interweb today. Did not know Concept Cars took several pics.



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I am still here, car has been in the shop since July. Attempting to fix the lean fuel mixture problem. As most of you know my car is 2.0 with hotter cams, 9:2-1 compression, header and a custom larger air flow meter, and FI. So there is no adjustability. So far I have had the header welded at the cracks , and heat coated, replaced the cracked rubber intake hose for the Mass air flow meter. Replaced the fuel injectors, fuel regulator, and filter, and some of the electronic sensors. Pluse the thermostat, next is welding the cracks in the muffler joint to the exhaust system. I don’t know if the lean mixture caused most of these problems, or the other way around.
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Ron Avery said:
I am still here, car has been in the shop since July. Attempting to fix the lean fuel mixture problem. As most of you know my car is 2.0 with hotter cams, 9:2-1 compression, header and a custom larger air flow meter, and FI. So there is no adjustability. So far I have had the header welded at the cracks , and heat coated, replaced the cracked rubber intake hose for the Mass air flow meter. Replaced the fuel injectors, fuel regulator, and filter, and some of the electronic sensors. Pluse the thermostat, next is welding the cracks in the muffler joint to the exhaust system. I don’t know if the lean mixture caused most of these problems, or the other way around.
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Cracked exhaust could be due to fuel mixture. Note this Exhaust Gas Temperature graph noting air/fuel ratio -vs- EGT.. yes, it's from the piston engine aircraft folks, regardless identical applies to vintage Dino juice fueled motors/engines.. For the piston engine folks, there is an EGT temp gauge on the instrument panel and a fuel mixture adjust to set/change this..
EGT vs mixture.jpeg


As previously mentioned, the proper way to set this up, figure out a way to adjust the EFI system's air/fuel ratio then take the car to a dyno to test for wheel power -vs- engine RPM -vs- air/fuel ratio and adjust as needed.


Bernice
 
Bernice,
thanks for the info, it has been difficult to trace this problem. As you know the Bosch FI from 1982, does not offer much if any adjustment ability. So that is why we have been replacing all the older and flawed parts. When Mark built the car back in the mid 1990’s until this last year it had run fine. There was evidence that the header had been repaired in the same areas that had cracked aging in 2023. Hopefully the repair was performed better this time. The shop that aplyied the the heat coating did the repair work. They felt confident that the have fixed the problem on the header.
 
Ron Avery said:
Bernice,
thanks for the info, it has been difficult to trace this problem. As you know the Bosch FI from 1982, does not offer much if any adjustment ability. So that is why we have been replacing all the older and flawed parts. When Mark built the car back in the mid 1990’s until this last year it had run fine. There was evidence that the header had been repaired in the same areas that had cracked aging in 2023. Hopefully the repair was performed better this time. The shop that aplyied the the heat coating did the repair work. They felt confident that the have fixed the problem on the header.
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Suspect this fuel mixture problem has been in this Bosch FI set up from day one, "ran fine" is relative. "Ran fine" does not mean extensive testing (sustained full throttle to sustained part throttle with varied environment and temperatures and humidity and air density due to elevation) on a chassis dyno or real world road conditions. Issues with many of these "lash ups", they lack the extensive testing oems do before any engine management system is allowed to be put on the market. Modern EFI systems have a significant advantage due to their software bend_ability coupled with the easy availability of chassis dynos and real time software monitoring allows for user engine management adjustments.

Cracked exhaust are a symptom instead of a problem. Cracked exhaust is likely due to the air/fuel mixture problem. As for cracks, once they begin, they are difficult to fix. Simple weld-up is not gonna work due to the differential hardness that often results from welding or the weld up cracks can prompt more cracks to occur.

Proper solution to this would be to sort out the air/fuel mixture issues and replace the exhaust. The exhaust system does have an effect on air/fuel mixtures and should be accounted for in the engine set up process. Identical applies to the intake as the whole thing works together as a system.


Bernice
 
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