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Fighting KR after a few mods

S

schlotzky

New member
1997 Buick PAU. Just finished installing SD headers, 3" high flow cat, 180* tstat, autolite 104s, intake, lightly ported supercharger housing outlet, and 3.4" pulley along with an Intense PCM and a bunch of new gaskets and maintenance items.
The car is running smoothly and as good as it did completely stock. The problem is, the car really doesn't feel any more powerful than stock.

I scanned using a Bluetooth adapter and Torque Pro and I'm seeing spikes in KR of up to 4-5* in 1st gear and as high as 6-7* under WOT in 2nd gear. Thinking it could be a fueling or o2 problem, I watched my AFR in torque and it's sitting at 14.7 at idle and 10.5-11 or 900mv under WOT which if anything seems rich and directs me away from a weak fuel pump, but besides that I'm at a loss. My pulley is really not very aggressive and with my mods I was expecting to be on the safe side of pulleys so something doesn't seem right. With Torque measuring my 0-60 with just my 180lb self, I got 7.7 seconds.

Here's a link to a 0-80 run monitoring my o2 voltage and KR. Sorry about the glare and shakiness, it may take a few plays. The KR peaked at 5.2 in the video and the o2 voltage seemed to stick around .9V at WOT.
https://drive.google.com/file/d/0B8V...w?usp=drivesdk

I was getting a P1133 immediately after fitting the headers which may point to the o2 but I'm reading of a lot of guys seeing this after header installs while the copper rtv burns off. The code comes back periodically, but even so wouldn't I be running rich and not getting so much KR?

I did test my fuel pressure, and it seems about right as well:

Key on, engine off, the pressure is 50 psi.

At idle, the fuel pressure sits at about 44 psi, and bumps up to 50 psi if I disconnect the vacuum line to the pressure regulator.

I ran a rough flow test by bleeding the line off the pressure tester into a wine bottle while the engine was at idle and came up with 43 seconds for 750mL. By my calculations, that's .275 gallons per minute or 62.6 Liters per hour. During this test, the pressure sat at about 10-15 psi (meaning my testing apparatus was resisting flow). I do not see any validity in this test at all for flow rate, but it's worth noting that the flow seemed consistent and I didn't see any aeration during the test or anything and the engine had no trouble maintaining smooth idle.

I did go ahead and order a new ACDelco upstream o2 sensor as the most logical explanation to me at this point is bad data coming from a faulty upstream sensor, but I don't have a lot of confidence in this.

Input?
 


sounds like you got to much timing in the tune. pulley back up to the stock size.

also make sure the o2 harness is not melted on the header. and check fuses, the one marked IGN. its for the maf and o2 sensor
 
The o2 extension harness I tested to be good, and has no signs of heat stress, nor the stock harness. The IGN fuse checks out as well.

As you can imagine, I'm resistant to renting the pulley puller again plus the hub removal plate just to put the stock pulley back on, as am I resistant to buying a stock sized pulley for my modular hub. I have no partial throttle KR so for now I can stay out of it or drive my other vehicle.

Should I ping Intense and inquire about the timing? When I emailed them they naturally tried to sell me a new fuel pump and o2 sensor.
 
this is why we don't bother with press on pulley's and make the plunge for the mps hub, because we never know how a car is going to respond to mods. we can make educated guesses, but every car is different. your car would make more power with a 3.5 pulley, or maybe you could get intense to pull some timing advance, would need to pull 1 degree of timing for each degree of kr seen.
 
In for subscribe. i have almost identical mods, I see about 1-2* KR at WOT, I think the tune could be better, but nobody tunes W-body around here and have been advised to stay away from mail order.....the PO had some kind of tune dine but damned if I know what.
 


most canned tunes come set to 18º wot timing. seems that can be to much some times. might be best off with stock timing.
 
I ordered my Intense PCM with stock WOT timing tables. I haven't returned my stock PCM yet so i could throw it back on and see if anything changes, but I wouldn't expect it to based on my aforementioned order preferences.
 
I put the stock PCM back in and went for a drive. KR peaked at 6.7* in first gear. Ambient was around 90*. I threw the stock airbox back in for a colder air intake system and saw a peak of 9* (yikes!).

So basically, stock tune had no effect. FWIW the o2 voltage was reading near 1V at WOT with the stock PCM, implying that I'm still running super rich despite getting tons of KR.
 


I have found that not all 3800s are created equal, after some research I found an article on ZZP non the less, that explained why these things happen, because of tolerances in how GM made the engines you will get things like head gaskets that hang over into the combustion chamber, misaligned intake and exhaust gaskets ect. I hear the head gasket one is pretty bad as the part that hangs into the combustion chamber is metal and it gets red hot and makes your fuel ignite before it is supposed to hence the large amount of kr.
 
best solution is a MAF tune so you can tune out the PE burst knock, optimize your timing tables, and get faster KR recovery.
Or, go old school and find an AFC 2.0 and re-shape the MAF signal for WOT
 
The o2 seems to have cured the code I was getting. After 8-10 ignition cycles and 80 or so miles, I don't have any active or pending codes. The KR on the other hand has not really changed. o2 readings at WOT remain pegged at 900mV. My long term fuel trims at idle and 1500RPM sit at -7.0%. I'll clean the MAF, but I'm seeing anything jump out.
 


After more testing, I'm actually getting quite a bit of part throttle KR I hadn't noticed before. 4th gear TCC locked at 60mph, 25% throttle acceleration I was getting as much as 3-3.5*of KR. At that point my calculated boost was less than 2psi which leads me to believe that even going back to the stock pulley isn't going to fix whatever is going on.
 
Your pulley is too small. Period. Your mods basically do nothing. If you want to run a 3.4 pulley with a canned tune, you need a big mod, such as a cam or intercooler. If you want to keep your pulley, you need more mods or get someone to add fuel and pull timing from your tune.

I tuned a car a couple months ago with your same mods. To keep it from knocking, I had to keep the afr in the upper 10's and timing around 11.
 
GTPpower said:
Your pulley is too small. Period. Your mods basically do nothing. If you want to run a 3.4 pulley with a canned tune, you need a big mod, such as a cam or intercooler. If you want to keep your pulley, you need more mods or get someone to add fuel and pull timing from your tune.

I tuned a car a couple months ago with your same mods. To keep it from knocking, I had to keep the afr in the upper 10's and timing around 11.
Click to expand...

Since the car feels exactly the same as it did stock after all this time and money spent, I'm ready to accept that I should have just kept it stock and I'll pulley up to a 3.5 or 3.6 as necessary. But as I just mentioned in my last post, I'm now seeing KR at 25% throttle at highway speeds when I'm not even in much boost at all, so would running a bigger pulley really fix it? To prove my theory, can I just pull the supercharger belt off and go for a drive and make sure I'm getting no KR? Would this tell me if perhaps my KR is false? Or is this not advisable?
 
Pretty normal to get kr under high load while cruising. A bigger pulley probably won't fix it.

Most kr is real. Pulling the belt is inconclusive. The motor torques way less without the blower, so the common issues that can cause false kr may not act up.

Fill up with race fuel if you really want to check for false kr.
 
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