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Old 03-11-2019, 04:15 PM   #1 (permalink)
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Default Frustratingly stumped - Need help!

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
19T
Vac reduction
DW 550 injectors
GM Z06 MA with MAFT.
CXR SMIC
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
New PTU
New coils
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.

So...

Possibly an injector that's stuck open?
Injector resistance pack crapped/crapping out?
MAFT failing?
Leaking BOV?

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
https://youtu.be/eIDXp9pPbGA

Thank you everyone in advance for your interest.

Last edited by UnlikelyDoc; 03-11-2019 at 10:07 PM. Reason: Added introduction
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Old 03-12-2019, 11:27 AM   #2 (permalink)
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Default Re: Frustratingly stumped - Need help!

To start with you should remove the BOV and install a OE-style recirculating valve. You can't use a BOV that vents to the atmosphere without tuning for it with a Chrome ecu, AEM, or some other standalone. I don't know if that's the only source of your problems, but I would start there.

FWIW, I'm using one of these: Mitsubishi OEM EVO 9 BOV 1545A001 (1545A001) - Ninja Performance - Affordable Performance Auto
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Old 03-12-2019, 11:58 AM   #3 (permalink)
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Default Re: Frustratingly stumped - Need help!

FWIW, the AFR should peg lean during coast down as the ECU shuts off the injectors.
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Old 03-12-2019, 02:20 PM   #4 (permalink)
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Default Re: Frustratingly stumped - Need help!

probably not the issue - but if your ECS suspension control unit is still plugged in - unplug it as a simple quick test and see if it makes any difference. ECS unit taps into your TPS sensor feed.
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Old 03-12-2019, 05:23 PM   #5 (permalink)
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Default Re: Frustratingly stumped - Need help!

I forgot to mention that the ECS computer has been removed.
I am gonna do a compression test when I get home. Didn’t get that taken care before vacation.
It seems something broke, failed, fried, or plugged up since it was such an immediate change.

Thanks for the input, guys. Keep it coming.
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Old 03-12-2019, 07:00 PM   #6 (permalink)
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Default Re: Frustratingly stumped - Need help!

Like Striker said, it's completely normal to go full lean on decel...which sounds like your original "issue". Not really an issue.
If your saying it goes lean while applying throttle, beegeezy is right, you can't run BOV to atmosphere when using draw thru (which is how most use the Z06 MAF)...although you didn't specify whether its in blow-thru or draw-thru.
Otherwise, whats your base correction and LO load values on the MAFT? You may just need to richen up the lo-load areas.
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Old 03-12-2019, 09:19 PM   #7 (permalink)
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Default Re: Frustratingly stumped - Need help!

I understand that it goes lean with deceleration. The problem was/is that it stayed there. The above linked video is at a 60 mph cruise. As you can see the AF swings from rich to lean while at constant throttle.
It’s running in draw-thru. The car was tuned and ran very well prior to this. The issue started after that “pull”. Prior to that it was running perfectly. Now the AF swings and there is a slight miss at idle, especially when cold.
I think it’s actually running rich but the miss is causing the “lean” AF and the rich reading is actually correct, but I am here asking those far more experienced than I.
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Old 03-13-2019, 06:43 AM   #8 (permalink)
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Default Re: Frustratingly stumped - Need help!

How was the car tuned? What tuning equipment are you using?


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Old 03-13-2019, 07:01 AM   #9 (permalink)
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Default Re: Frustratingly stumped - Need help!

Have you logged it at the same time to make sure the gauge/sensor are good? You should see this on the narrow bands as well.
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Old 03-13-2019, 08:17 AM   #10 (permalink)
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Default Re: Frustratingly stumped - Need help!

All of the attached logs are after the AFR problems started. There are two logs at highway speed and one at idle after a drive. I don’t have a whole lot of experience with logging. Hoping someone can look at the logs and quickly see a problem and steer me in the right direction. When I get home from vacation I’ll log a nice 20 min or so drive and post it up.

Beegeezy, the car was dyno tuned prior to me getting it. Stock ECU and the MAFT. I have Evoscan for logging.
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