Hmmm....necro bump commencing
let me just....
There that's better.
Well almost 4 years later I'm back to share my mostly completed project. I won't go into ALL of the details on this thing but rest assured that it was a nearly nuts and bolts restoration/modification/upgrade that went into full effect starting in the fall of 2014. The project consisted of but not limited to:
complete chassis/suspension/brake/diff upgrades
body work including new rocker panels, genuine Cossie bumpers, and many hours modifying XR rear quarters for Sierra rear glass, plus paint prep and all that, painted in Dodge "Scarlet Red"
YBB engine completely overhauled, includes Cosworth Racing 1mm overbore pistons, ARP studs, GT35R turbo, AS plenum, Airtec RS500 intercooler and rad etc.
custom trimmed seats and complete Auto Meter gauge package.
On to pics:
Now that she is on the road.....I'm running into some pretty tough to solve issues. I have quietly been searching through old threads but I'm coming up empty. The engine has a very scary lean condition at certain points most concerning at high RPM/boost. Whats more, it seems to match with a dodgy rev counter. Now I know what you're thinking....but I've tried that, I feel that it's got to be in the wiring harness somewhere but maybe someone has better insight? Here are relevant details:
fully rebuilt YBB 8:1 compression
GT35R turbo with 18psi actuator
L8 computer on what must be L1 3-door engine harness (no closed loop, knock etc)
Bayjoo stage 3 with greens and 3 bar MAP, amal valve
All sensors replaced including CPS and Phase sensor (all correct gaps)
Grp A coil
AEM rising rate fuel pressure regulator (gauge on regulator but no gauge in interior) set to correct base fuel pressure
Walbro 255 LPH in-tank fuel pump
uprated plugs gapped correctly from what I can tell
correct TPS for L8, wired correctly
Autometer rev counter connected to original green signal wire from coil
AEM wideband O2 sensor and boost gauge
So what happens....well the engine runs beautifully except for a few areas. The rev counter will occasionally bounce at various RPM...mostly OFF of boost. Once on boost, the revs are smooth as silk (so it can't necessarily be a plug gap issue), SAME with air fuel ratio, it sticks around 12 when going from 1-say 18psi...as long as I'm not reving above say 5,500RPM, At upper revs, the rev counter goes crazy bouncing and the fuel ratio gets scary LEAN
. at "tip-in", just barely touching the throttle, the rev counter will bounce and the fuel will go stupid lean, once applying modest throttle and getting into boost, the ratio returns to safe, foot off the throttle into vacuum (-20) and ratio stays safe, it's that initial "tip-in" throttle where the lean condition happens most
I had assumed that the signal from CPS to ecu was causing the computer to misfire and cut fuel, but I've checked and rechecked the gaps, they are perfect and the sensors are brand new. It's still got to be related to that but what else should I do? I can't just throw a bunch of parts at the problems hoping they will eventually be fixed though my long term plan is to do something like a LINK system so I can do my own tuning on my side of the pond. I'm not ready for all of that yet, I'd like to see if I can get this thing sorted first.
I know my harness is a bit suspect as I wasn't the one who originally fitted the YBB to the Merkur but I'm not sure a new harness will fix it. Should I look at the coil? the IGN module? TPS? I've had a long standing issue using the ISCV, even new ones won't work correctly, I'm thinking the wiring may be reversed. I need to read fuel pressure during these lean events. Any suggestions would be more than appreciated, I know "Cosworth Misfire" is a pretty common thread title.