KGRESOCK

Here is my dilema......
Iv'e been chasing a "vacuum leak"
Why? Because mechanically I'm measuring 9/10"
at idle.
BUT>>>
Per my scans (datamaster/scanmaster)
Bar = 30.0 and Map = 14.5 therefore
Bar-Map =15.5" (normal)
Why am/ I reading so much lower mechanically????
Any insight would be appreciated.
I haven't gone into too much detail here
because I don't want to bias anyone's thought
process.
Lil help please
Kevin

Hot Rod Hawk

Need duration at .050 numbers:
centerline at:
LSA at:

Closed throttle timing your running from the far left of that table across the first four cells to the right:

Lets see this first

Hot Rod Hawk

Are you testing vac with a hand held toolbox guage or a autometer dash guage?

Are you testing with the PCV operational or Blocked?
A bad PCV will drop vac reading

KGRESOCK

duration at .050 numbers:
centerline at:
LSA at:

Closed throttle timing your running from the far left of that table across the first four cells to the right:

Lets see this first


__________________

Hot cam 218/228 525/525 112
Your second question ....could you elaborate?
PCV is operational and I'm using a autometer gage.
Kevin

Hot Rod Hawk

Operational PCV...
...are you running one and if you are have you tried a new one?
Easy thing to do would be pull the line off the PVC and plug it with a 5/16 thread bolt so its elminiated as a possible source for the leak.
Of course leave the PVC in the rubber gromet where its located on the side of the intake , put a vac cap on the open side where the source line attached.

Now retest with your vac guage.
Is your reading better now and how much better?

The second question...
You have LT1 edit, right?
if so look at the "closed throttle" timing page. its just a single row left to right. What timing are you running in the first 4 from the left heading to the right?

KGRESOCK

Jeff,
Iv'e got my hands on a new pcv,map sensor, and
another vacuum gage. I'll post my results tomorrow.

No LT1 Edit (yet).
Thanks for your help

Kevin

KGRESOCK

Today's results.
All readings taken from scanmaster after warm up
@idle 900 rpm

1. PCV change= no change
2. Check with new vacuum gage
Mechanical vacuum = 14.5/15"
Map= 14/14.2
Bar= 30.1
TPS= .62/.64
Maf= 6

3. Install another Map sensor, Idle did seem too
smooth a little
Map= 14.2
Bar=30.1
Vacuum= 14.5/15
TPS=.62/.64
Maf = 6

4. Check old vacuum gage off of same line used for new gage
old gage reads 11"

Good news is vacuum is ok must be something wrong with the
autometer gage.

Bad news is I got nothing to pinpoint the 4900/5100 RPM stumble
I'm trying to track down.
Side note: IDlE BLM's @149/151
Can you point me in a direction please.
Thanks
Kevin

taner

the more i think (which can be a scary thing, lol) the more i believe it is related to the tune up on the pcm. higher BLM's mean it is adding fuel correct? i always seem to get it confused. you see what happens when i start thinking, ha ha!

Hot Rod Hawk

Block learn works from 128, this is zero percent corection to the fuel table. They mean nothing during WOT and everything at light load/part throttle operation.

Above 128 the ecm can correct up to +24% fuel correction with 160 being a max reading for this.
Below 128 the ecm can subtract up to -24% fuel correction with 108 being the value for this.

The mis your talking about is at WOT at the 5xxx rpm reading correct?
By chance what is the injector duty at.... "MS" value your seeing at the miss?
.18 ms would put you at 80 percent duty cycle on the injectors
.22 ms or higher means your out of injector and running at 100% duty cycle.

Kevin try adding 20 percent to the injector balance table for "idle" operation and you should see the block learn get driven back towards 128. I adjust that in till I see the car running 124~126 ish at idle.

Jeff

KGRESOCK

Taner,
yes high BLM's mean the puter is seeing a lean condition and
adding fuel. This is why the potentail for a vacuum leak
seemed definate. After my "little test" I have ruled this out.


Got another point to add...
Reviewed numerous datamaster logs last night , this stood out

Older scans when reviewed at WOT show a "steady" L/R o2
reading 900to 950 this was before the WOT hesitation issue
started. I also looked at other peoples scans @WOT same thing.

Scans from this year show serious drops in 02 voltage which seem to correspond with the hesistation values dropping as
low as 600.
I had also thrown a code at M8. DTC 55 lean condition during
PE mode. My next step is to review the voltage before/after
the 02 reading drop. I'm wondering if my issue is fuel delivery
related.
Any one got 2cents on this ?
Kevin

Hot Rod Hawk

DTC55 is sign fuelpumps volume is failing you most likley. This is probley whats causing the idle bl's to show lean also!
What fuel pump are you running?

KGRESOCK

Hawk,
When I was running 24's my duty cycles were well above
80%( as high as 98%)
Currently I am running 30's and the duty cycles stay around
70% at WOT.
Are the 02 values I'm seeing at WOT useful???

Let me define the problem and provide a little background.

Issue is WOT high RPM stumble. Car just falls flat and then picks
back up.
I ruled out ignition after going to the LTCC. I ruled out injector
issues ( high duty cycles) by going to 30's.
I am currently narrowing down my search to the following 2 items.

1. Voltage drop from the pump during WOT.
2. Lack of "bucket " on my walbro perhaps causing a fuel slosh
condition.

Any other items you might suggest?
Kevin

Hot Rod Hawk

Rule out fuel slosh by filling the tank 3/4 full and see if you get the surging. Verify voltage at the pump and if that looks to be low you could try would be running a "hot wire" setup off the bat terminal of the alt to a heavy duty relay that would power the fuel pump. This type of setup works wonders for incressing fuel output stabilty... call me if you need a hotwire set up.

if you rule out slosh and voltage it has to be pump.

KGRESOCK

Hawk,
Thanks for the input. Definatelty interested in the "hot" wire
set up. I'll give you a call tomorrow.
Thanks
Kevin

taner

but kevin has a good pump in it already?