icanthelpitigottatellya!

[gmctd]

Folks, that Tech-II is some wondermous piece of appliance!

As some may remember (and to those that are bored with being reminded, I say tongue.gif ), I ground-up built my truck, including interfacing the factory '95 PCM to the older vehicle wiring and instruments.
This tends to put one in a different frame of mind at each instance of getting behind the steering wheel - are the '89 instruments correct, is the '86 Blazer tach accurate, does the '91 quartz speedo directly interface with the '95 VSSB and PCM digital ratios?

If I were of a timid nature, I'd just use the van, reserving the truck only for backing out to the mailbox every day.

Well, folks - I am now justified!, certified!, personified!, and satisfied! (for now - so much time, so many upgrades wanting!)

In short, and to wit:

Tech2=65mph.....speedo=65mph
Tech2=2250rpm...Tach=2450rpm ???
Tech2=177deg....Temp=187deg eng coolant temp
Tech2=165deg....Temp=165deg intake air temp
Tech2=13.4v.....Gage=13.4v system voltage
Tech2=21psi.....Gage=7psi Boost (+14 Baro)
Tech2=182ms inj pulse width
Tech2=28mmx3 fuel rate
Tech2=10deg inj timing
Tech2=-1.5deg TDC Offset
Tech2= 0 number of cam pulses missed
Tech2=107deg fuel temp

And a bunch of other stuff which I've forgotten - too many numbers, too much data from one 40mile trip!

One History DTC-16 Vehicle Speed Sensor Buffer fault, probably from switching ratios from non-o\d to overdrive, and back.

That 200rpm hi on the tach has always kept me wondering at the rpm\mph you guys were getting outta 235\85R16 shoes.
I've popped the diff covers twice, counting R&P teeth, at first not believing the oem-stamped numbers - 41:10 = 4.10 ratio.

Tach input is from Crank Position Sensor input at PCM, so a tweaker in the integration\meter drive buffer oughta do the trick.

Coolant temp reading high? Safety margin, being that it's 10deg higher than actual.

Yep - elation is it's own reward! :cool:

Oh, yeah - the Subject lead-in? "I can't help it I gotta tell ya!" You know - the New York Deli TV ads.

[ 01-18-2004, 08:06 PM: Message edited by: gmctd ]

[EWC]

Where does the tach get its signal from ? Maybe wrong diameter alt pulley ?

[gmctd]

The tach is from '86 V8 Blazer - takes 4 pulses per crank rotation from ign coil.
I designed a buffer to adapt the output from the 6.5 Crank Position Sensor, also 4 pulses per rev for the PCM.

The internal tach circuitry is fast, but I didn't know that until today. Tech-II engine rpm matches Paul's diameter\rpm\mph calculator.

My real concern was that GM, constantly
'improving' stuff, had changed the quartz electronic speedo circuitry thru '95 such that the '91 speedo required lower or higher digital frequency input.
This would mean VSSB output, adjusted so the '91 speedo read 65 for 65mph, was sending PCM a frequency equal to 40mph. Or 80mph.
PCM would be pulling injection info - fuel rate, timing, boost, etc - from maps at wrong data points, affecting output power and economy.

It was a big relief, verifying all that after 4years (April), almost 40k miles and umpteen tanks of fuel.

Also of some concern is that I can pull 20psi boost without setting DTC-78.
Fortunately I have access to a Tech-II, so various PCM aspects are becoming clear.

[ 01-18-2004, 06:41 PM: Message edited by: gmctd ]

[EWC]

Yikes , I just read your post again . I thought I was going to have a problem putting a 4L80E in my 83 GMC dually . After looking at your truck , very nice by the way , I don't feel so bad . I see what you mean about getting all the systems to communicate with each other . You're probably right , a little more tweaking and you'll have it .

[gmctd]

Thanks.

You may already know this - the '91 thru '93, and upward in some vans, had stand-alone 4l80E computers, with correct inj pump-mounted accel position modules.

'91 Subs, and probably Blazers and CC, have quartz electronic speedo, taking output from VSSB.
The complete inst cluster is direct bolt in for the '87 back trucks - helps if you get the complete inside\outside wiring harnes, also direct bolt-in thru the firewall bulkhead.

Got a 4L80E for mine, but for now the T400 and aux o\d is working well. Used PCM from '95 K6.5LTD with 5sp manual - no auto trans DTC's.

Good luck with yours.

[ 01-19-2004, 08:18 AM: Message edited by: gmctd ]