This has not been a good summer for the coupe. Since moving to Denver, the V12 has not been running well….and then there was the breakdown on the freeway. Let’s start with that….
The weekend of the Rocky Mountain Airport car show, the engine was running rough. There was hesitation on light acceleration and some backfiring at low speed, low RPM acceleration. Generally, not the happy situation we had last summer with the car. Driving back from the show, the car started hesitating on the freeway so I pulled into the emergency lane and it stalled. We called a tow truck and I did some remedial troubleshooting while we waited. There was only about 20 psi in the fuel rail (should be around 31 psi) even though the fuel pump was turning on as it should (and is relatively new). The most likely culprit was the fuel pressure regulator. We get towed home and when I try starting up the car again, the fuel pressure holds at 31 psi and the car starts….OK time to replace the regulator.
Let’s back up to the beginning of the summer. The coupe ran poorly as soon as we moved to Denver. I checked the spark plugs and they were very fouled. I was running slightly higher fuel pressure than stock, so my working theory was that the additional elevation (5,000 ft vs 3,500 ft in Calgary) and higher fuel pressure was causing the problem. I reset the fuel pressure to stock (30.8 psi), replaced the spark plugs and did a full Sea Foam treatment, but the car still ran poorly.
Then came the freeway breakdown. I am using one of the stock Bosch fuel pressure regulators with my fuel rail upgrade, where the original setup used two. I have had a slight concern that maybe a single regulator is not up the handling the full flow requirements of this engine. Well if nothing else…its a good excuse for an upgrade.
I selected the Holley 12-886 as it is rated to be adjustable from 15 to 60psi. That’s plenty of range for my application. Unfortunately, I was not able to get the pressure adjusted any lower than about 33 psi. Both Holley and Jegs were great, and agreed there must be a problem with the regulator, so I returned it without any hassle. After reinstalling, the new one could only adjust down to a little over 30 psi. Since that was my target, I will leave it in for now.
The car still ran rough, so decided to look at the plugs again. They looked slightly fouled this time, so again I changed them out. This didn’t seem to help the rough running.
I had a spare throttle switch, and my current switch was hard to calibrate at the idle point. It was a long shot, but I calibrated the replacement and replaced the switch. My idle was was lower (that was a good sign) so I adjusted that back up to around 800 rpm at the AAV adjustment bolt. After all that, the car is still not running well.
This is where I am today. Pretty frustrated at this point and reading through my copy of Bosch Fuel Injection & Engine Management hoping for inspiration.
Would love any suggestions you may have. Should also start posting on the forums for suggestions……more to come.
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