RE: Ask the Car Guy @socky July 30
Hi sir, I have this ongoing issue still unable to resolve.
Problem : Engine feels like bogging, like mini misfires during full boost. The engine sounds like you blowing your lips 'blublublublublu'. 1st and 2nd gear happens at 4k RPM, 3rd and 4th gear happens at 3.5k. 5th gear happens at 3k. If rev slowly until redline, it wont have this issue.
Car : Nissan Cefiro A31
Year : 1991
Engine : RB25DET NEO (From Skyline R34 GT-T)
Here's a list of what has been done
-Changed new wiring (had some shortage due to rat bites, removed ignitor of R33 S1)
-Change ignition coils (From R33 Series 1 coils to R34 NEO, was using R33 Wiring System previously, funny previous owner)
-Replaced a cracked hose on the vacuum line of wastegate
Upcoming checks
-Air fuel ratio (clip on exhaust)
-Boost meter (will borrow from a friend, mine faulty)
Suspect :
-Fuel pump going bad
-Minor boost leak from intake pipings
-ECU tuning went off? (is this possible? last tuned last year October)
Addon : This issue started when my car battery starts to go weak. I have replaced it with a new one, still no go
You have converted the engine, converted the wiring, converted the coils. There are so many variables added to this bag of mixed parts, it will be difficult to diagnose.
You need to address the battery issue. Why did the problem come about when the battery went weak? Perhaps there is a reason the battery went bad. Perhaps you have added a load to the battery that you didn't have before. There could still be bad wiring. The alternator could be going bad.
Verify the easy stuff. Fuel pressure, boost pressure, ECU codes.
If none of these things are bad, start looking at the more difficult things like injector flow, air/fuel ratio at boost, fuel pressure at boost, spark delivery, timing curve at boost, pressure testing your boost pluming, verify no exhaust leaks between engine and turbo, and check for turbo damage.
I've built plenty of frankensteins before and can tell you first hand how difficult they are to troubleshoot when something goes wrong. There is no simple answer that can be given. You need to verify every subsystem is functioning properly one at a time to narrow down the issue. Start with the easiest and simplest subsystems to test even if you don't think it has anything to do with the issue. This way you eliminate those possibilities.
I recall a guy that had an engine problem and asked for help. I noticed that his engine was very clean. Eventually the guy admitted that he had detailed his engine and the problem wasn't present until he detailed his engine. On closer inspection, I founded a wire that was pinched under the valve cover. I discovered that the guy removed the valve cover to clean it thoroughly. When he put it back on, he pinched the wire and shorted it. The relevance of this story is that you may already know what has changed since the problem started. Think back and review everything that was done just prior to this problem.
Thank you for such a brief explanation!