Update on Zilla's porting and lean/KR problems - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 10-07-2005, 12:53 AM   #1
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Default Update on Zilla'* porting and lean/KR problems

As many of you know, I did some major port-matching on the LIM of the Zilla some time ago, and also my Exhaust manifolds. In addition, I did some INSANE porting on the TB.

Since the car came back from trans building, I've had a slight lean condition that I believe is contributing to KR above mid-throttle.

Today I finally went and got a fuel pressure tester:

Ignition on, engine off spec: 41-47 psi.
Zilla'* actual reading: 42psi, and it drops within 2 seconds to 20psi after the pump primes.

At idle, I have 39 psi, and it only rises to 43 when the vacuum line is removed from the regulator.

My gut tells me I have a weak fuel pump AND a leaky FPR. And that should solve the rest of the problems.

If you're considering porting the top end for 20% more flow on a Series 1 L67 like I did, make sure you have the fuel capacity to back it up. It might have been just enough before the porting, but it isn't now.
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Old 10-07-2005, 12:56 AM   #2
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Consuming any oil?

(now I sound like na95sta)
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Old 10-07-2005, 12:57 AM   #3
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No oil loss whatsoever.
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Old 10-07-2005, 01:02 AM   #4
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Quote:
Originally Posted by jwikoff99
Consuming any oil?

(now I sound like na95sta)
haha.

Bill, did you check the fuel pressure?
What are your block learn multiplier #'* at idle and midrange?
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Old 10-07-2005, 01:12 AM   #5
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I don't have that data in an OBD1. But all the fuel trims show the same as the symptoms. Lean.

Read my first post for the fuel pressures.
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Old 10-07-2005, 01:14 AM   #6
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Wow, that is very low pressure.
Your fuel pump should be pushing out 60 psi.
I have mine regulated to 54 psi with the vac line off. That'* about 5 psi higher than it was when stock.
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Old 10-07-2005, 01:18 AM   #7
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I'm certain that will solve the last bugs in the Zilla'* return.

Should be quite the tire smoker when I'm done. The funny thing is that it feels at least as strong if not stronger than before all the work already. And that'* running lean.
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Old 10-07-2005, 09:50 AM   #8
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I agree, you do have a fuel delivery problem... It will get worst when the engine is warm and during acceleration.
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Old 10-07-2005, 11:17 AM   #9
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Quote:
Originally Posted by ssei1995
I agree, you do have a fuel delivery problem... It will get worst when the engine is warm and during acceleration.
.....and when the pump isn't fully submerged in the cooling sensation of 102 octane.

So what pump are you getting? The Walbro 255 LPH High Pressure pump? Also did you consider taking your original FPR and putting it in a vise to crush it a little bit to get some more psi for the time until you get a new FPR?
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Old 10-07-2005, 12:12 PM   #10
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Interesting stuff:

I checked the 95 this morning for a comparison point. It'* even worse.....BUT it doesn't have the fuel demand the 93 does. I'm still totally stock on the 95. I'm not sure either regulator is truly bad yet, but the pumps are certainly weak on both cars. Not surprising when you consider the 95 has more miles than the 93.

And keep in mind, I ran at Woodburn in the 95 with crappy fuel pressure. VERY crappy.

I'm looking at the Walbro, but I want solid numbers for comparison between pumps first, both Pressure and Flow rate. OEM vs. Walbro, considering they're basically the same price. Also, IIRC, the Walbro has an adapter harness that has to be spliced in, and I'm not sure if the strainer sock (OEM) attaches to it. I've got some feelers out on this stuff.
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