First off I’d like to thank the community for the abundance of knowledge here and the willingness to share it. My name is Adam. I, like most of us, fell in love with these cars while in high school. Bought my first one, a pearl white 98 in 1999. Had that for a couple years and sold it not long after getting married. I’ve always wanted another one. Well life has finally stabilized some and I have some expendable income so, I picked up this 94 a year ago. Had a couple issues that got sorted, but overall the car has been great....until recently.
I’ve been lurking here on the site for two years now and have searched extensively. Either the issues weren’t exactly the same or the original poster never posted a resolution. I am now reaching out for help.
Here's the car:
1994 VR4 w/ 111k on the clock
Walbro 400 FP
DW 550 injectors
GM Z06 MA with MAFT.
Some type of aftermarket BOV to atmosphere (previous owner installed)
Here's the problem:
Late last full I pulled away from a stop and ran first gear up. Not full throttle and not to 7k+. I would say 3/4 throttle and shifted around 6500. The car pulled strong with no issues. I grabbed 2nd and let the car coast back down. I then noticed my WB gauge was off the chart lean. The car continued to run well. It got me to and from work that day. I actually thought it was my gauge at first, but then noticed the miss at idle. Unfortunately we all know how those gauges can lie when there's a miss. There's no CEL and the car continues to run well. No miss under load that I can sense, although I haven't been too hard on it since this started.
Here's what I've done thus far:
New plugs and wires
Fuel pump and filter are new
New Aeromotive FPR (Thanks, Chris at Rvenge, for putting this kit together!)
Pulled the ECU - no leaking capacitors. ECU looks really good for 25 years old. It might have had some work done to it.
Boost leak test - nothing found
Manifold vac is the same as prior to current issue (-18 to -17 at idle)
Timing marks on cams are all lined up
The back three injector resistance was 2.0 across the board. I haven't tested the front three yet. I know, I need to do that.
What I am thinking...
Prior to the FPR being replaced the FP was ~43-45 with vac. It was still the OEM FPR and pressure didn't change when vac was removed. The WB gauge read full lean 99% of the time with random swings to full rich. I figured I was overrunning the stocker and the car was so rich it was missing and causing all my issues. The new FPR didn't fix it. With the new FPR the WB gauge has a lot more movement. It still reads full lean a lot of the time, but will now swing back and forth from lean to rich more frequently. Every once in a while it will hoover around 14.5 at idle, but as soon as I blip the throttle all is lost and it goes full lean again.
Possibly an injector that's stuck open?
Injector resistance pack crapped/crapping out?
I need ideas of where to look/test next, guys.
I have attached three logs. One is a short 12 min highway drive. The second one is also a short drive. The third one is at idle after driving 20 to 25 min.
link to a driving video
Thank you everyone in advance for your interest.