As part of dropping off the Wagovan at a mechanic tomorrow, I’ve typed up a summary document for it. The hope here is that it’ll help the techs know what has been done, but at the same time I wonder if going at it with virgin eyes would be better? What does Oppo think? (Summary below)
Primary Symptom Summary:
At sustained, high throttle the engine loses power and begins to backfire though the intake. Hereby referred to as “the problem.”
Easiest way to replicate:
80% throttle, 5th gear, on the highway. Long uphill sections make it happen faster. Full throttle briefly solves the problem… sometimes.
Related recent work:
- Fuel system drained
- Carburetor replaced/ converted (Weber DGEV 32/36)
- Exhaust replaced
- Fuel pump replaced
- Fuel tank to hard line replaced
- OE Fuel Filter deleted
- In-engine compartment fuel filter added
- Fuel return check valve replaced
- Spark plug wires replaced
- Spark plugs replaced
- Distributor cap replaced
- Distributor rotor replaced
- Distributor replaced
- Reluctor replaced
- Ignition module replaced
- Condenser checked (0.48uF) but not replaced (part NLA)
- Ignition coil replaced
- Valves Adjusted
- Valve cover gasket replaced
- Oil change
- Air filter replaced/ upgraded
- Fuel system checked
- Return not plugged – 2.9 PSI
- Return plugged – 3.9 PSI
- Flow - ~ 10+ oz per 60 seconds
- Block cleaned and re-terminated
- Battery ground connector replaced
- Exhaust system checked for obstruction (cat back, cat was not checked)
Heresy and subterfuge:
Problem seems to be getting worse.
Problem went away completely after replacing the cap, rotor, wires, coil, plugs, and adjusting the valves, but came back after adjusting the timing. Changing the timing back did not restore “normal” functionality. At that time, the carburetor seemed to want to be ran much leaner and the idle was hunting. None of this made any sense, but led to the replacement of the distributor, which didn’t seem to help.
Manifold vacuum was checked and was steady at 20 in Hg at idle. Vacuum dropped considerably when the engine was revved, however.
Pulled the #3 plug on Friday (4/12) and plug look like it had been running very lean/ hot, with some blistering on the insulator.
Bypassing the crankcase ventilation solves the problem with bogging when the accelerator pump kicks in (known issue with a weber conversion) but doesn’t solve the problem.
As this problem started after I had the new exhaust put on, I this became my immediate suspicion. I took it back to the exhaust shop and they were happy with the tailpipe flow. Still we temporarily removed the exhaust, but not the OE CAT as it is built into the manifold, and the problem did not go away.
At this point I am fairly convinced that the problem is in the carburetor, but I am certainly open to suggestions.