88 Buick Vin 3 Stalling Followup(a bit long)

[Lynn R. Erickson]

Wow what a great group of people on this mailing list!

Thanks for all the great input. I've learned more in a week on this list
and searching the archives than I did in two years of on and off web
surfing.

At the end of the followup are some new things I learned.

Here's some followup on list member's suggestions:

peter paul fenske <ffnsp955 at bcit.bc.ca> wrote:

>What are you MAF readings.

Around 4 gps -- eyeball reasonable

>Some of the stuff we came up was worn valve guides and
>vacum leaks. 

Bit the bullet and did a thorough vacuum leak check -- plug off and
stethoscope -- no joy. Engine is a pampered 3000 mile oil change unit.
Hope the guides are OK.

>But to be honest idle was still not the best
>As a clinch we cranked up the idle spd in the
>ecm.

See "New Knowlege" below.

"TBK" <terryk at foothill.net> wrote:

>10" is low at sea level. Should be around 15 or above. Intake gaskets >were
>prone to leaking. Does the idle change if you remove the oil cap from >the
>valve cover? Disconnect the tranny vacuum modulator and plug the line >to the
>intake. Does the idle change? Is there oil in the vac mod line? Is >there oil
>in the throttle body?

As noted above. No apparent vacuum leaks.

"TBK" <terryk at foothill.net> wrote:

>IAT temp could be from fan blowing radiator heat on the air cleaner and
>hose. I get the same effect when stopped. I should drop once you get >moving.

See "New Knowlege" below.

>Bulletin 88-7125-2 TCC engages in shift to reverse or drive (125C >only). Bet
>you have a 440.

Yep. It's a 440.

Clare Snyder <snyder at huron.net> wrote:

>The ECU/Prom would be my first step - they have been problems. The ecu
>can not check itself, so if no codes and intermittent problems it >points
>there. Likely a bad solder joint or cracked trace on a PCB.

See end of this e-mail.

"TBK" <terryk at foothill.net> wrote:

>Go in and tap the ECM. Not BASH, but tap.

First thing I did. Way back. This is even an official GM test procedure.

>There is a bulletin for loose fitting connector pins on the ECM.

Yes. The ALLDATA CD has that one. The missing one is Buick 87-6E-8 or
Olds 87-T-30. Wiggle test doesn't show any connector problems.

"Bruce Plecan" <nacelp at bright.net>

>There are very few cars that I've worked on that I couldn't get right,
>and you own one of them.  The best results I had were changing the
>IAC to a different pintle design.

I'll keep that in mind. Hope I don't have to go to that extreme. Off
idle this is a very nice healthy engine. No 13 second quarter miles, but
definitely adequate on the freeway.

Frederic Breitwieser <frederic.breitwieser at xephic.dynip.com> wrote:

>The consensus of the other two replies you recieved I believe are >correct -
>check for vaccuum leaks first.  Common places on the 3.8L SFI is the >vaccum
>resevior hose at the resevior, the engine I pulled (an 86 from a >LeSabre)
>was missing a plastic clip - as well as three others in the junkyard, >and
>one other vehicle had it.  Also check your vacuum booster.  Mine leaked
>horribly.

As mentioned above, no leaks that I can find.

Thomas Matthews <Tmatthe1 at worldnet.att.net> wrote:

>Lynn, have you tested the MAF? while it is idling, rap it firmly a
>few times... if it stalls, it's bad... I've seen this many times.

And TWong29770 at aol.com wrote:

>I forgot, one more thing to check is the MAF sensor, check it by >lightly
>tapping the body of the MAF sensor while the engine is idling.  If >there is a
>problem with the MAF the engine will stall when you tap it.  Use a >large
>screwdriver handle or a rubber mallet,  I mean TAP not BASH!

I've been the MAF fail route before. Twice. The first time it loaded up
and ran full fuel. I dug out the Chilton's and web searched for
diagnostic procedures. WRONG! They said to look for a varying voltage
from the MAF - NOT. Because the ouput signal from the MAF is variable
frequency so it always reads about 2.5 volts. Of course I only found
this out later, but replaced the MAF and it was indeed the problem. The
cheapo replacement unit crapped out about 3 months later by cutting out
completely (engine died at 75 MPH). It started back up after a cool
down, and this time the tap test was completely effective.

>Also TPS volts are a little low, might want to adjust TPS. 

If my latest work doesn't do any good, I'll try it.

>Also check fuel pressure at idle with vacuum line on and off,

Did that. Checks OK

> and I also suspect a injector dripping... 

My dad had this checked -- no luck.

>These engines are VERY, VERY nice when running right...

Agreed.

>IAT temp being high is likely heat soak of sensor.

See "New Knowlege" below.

TWong29770 at aol.com wrote:

>Is your Buick the V6 that is port injected and has DIS ignition??  If >so you
>may want to try replacing the DIS module which is the module that is >what the
>coils are mounted to.  As far as the rough idle, has anyone checked out >the
>injectors yet?  You may have a fouled injector, or possibly a vacuum >leak.
>Your 10"hg sounds low for this engine, it should be around 15-18"hg >when its idling smooth.

See above on vacuum and injectors. If replacing the ECM doesn't work,
the DIS is my next step.

"Slava" <cittt at cityline.ru> wrote:

>>10" hg manifold pressure at idle. Is this normal? Reading taken from
>>transmission vacuum line.

>It's absolutely normal for idle. My engine has 10.3"

Thanks for the information. A Buick 3.8 in Russia? I was in Moscow a
couple of years ago on business, and the only American cars I saw were
Mafia Blazers.

"Gregory A. Parmer" <gparmer at acesag.auburn.edu> wrote:

> Is that the 7783?  I posted a bin to the ftp site
>for a 7783 that I *think* musta been a service
>release---the code on the eprom was different
>than that on the ECM itself.

Tis indeed the 7783. Can't find your file in the ftp stuff.

>FWIW, I think the wiring harness has a bad wire to one of the
>injectors. Seems to be "open" where the bundle of wires went thru the >firewall.

Wiggle test doesn't show up anything. I dread the thought of trying a
continuity test on the whole harness.

>If you need the 7783akba.bin just lemme know.

Would love to have it, although my prom is the AKAY. The AKAB _does_ run
the engine though. My junkyard ECM came with the AKAB and I tried it out
just for the hell of it.

>Some harness specifics (pinouts and such) are on my website....
>http://www.acesag.auburn.edu/~gparmer

Great site! Thanks.

shannen <Shannenj at mcn.net> wrote:

>I have always found that a component which you _know_ is bad, but which
>exhibits no symptoms whatsoever, will always require replacement after >two or three good bashes.

Absolutely. One of my favorite techniques. As the old saying goes
(apologies to Frederic Breitwieser), don't use force, get a bigger
hammer. 

"TBK" <terryk at foothill.net> wrote:

The flickering CE lamp leads me to the ECM or connectors or power loss.

Oh lordy I hope I don't have to find an intermittent connection!

NEW KNOWLEGE

Some new things I've learned that may be of value to others:

Keep in mind that all scanner work was with the car stationary. I don't
have a laptop yet. :-( The scanning was done using a friend's Diacom
setup, and I didn't have the manual. The Buick has a 783 ECM with the
AKAY PROM.

When the scanner communicated with the ECM the engine RPM would rise,
and the readout indicated ALDL mode. The scanner also sets diagnostic
and backup modes. Searching the archives, I found information showing
that placing various resistances from the diagnostic test (pin B of the
ALDL connector) to ground (pin A) caused the ECM to go into different
modes. Specifically: Normal Mode (R >=20K) ALDL Mode (R==10K) Backup
Mode (R==3.9K) Field Service or shorted mode (R<=500). The light bulb
went on. I could just put a 10K resistor across the A and B terminals
and raise the idle, and maybe that way the engine wouldn't stall. DO NOT
TRY THIS AT HOME! It makes the car barely driveable! Shift points
screwed up, 30 MPH idle, who knows what else. Didn't take me long to
yank that resistor out of the connector. 

Interestingly, the software did not have a "normal" mode. So I disabled
the pin B connection, and hooked the scanner back up to the car.
Interesting differences in the readings vs. mode:

No mode readout. Just "----" displayed.
Intake air temperature was accurate. I suspect the ALDL mode puts a
selfheating current on the IAT thermistor causing the high readings I
was seeing after time in the ALDL mode.
Idle was 750 RPM vs. 1000 in ALDL mode.
Spark advance was 0 vs. 28.6 deg.
EGR duty cycle 79% vs. 0%. I think this is ported vacuum, so it doesn't
make any difference in how the engine runs at idle.

So those of you running Diacom scanner software might want to try
disabling the ALDL pin B. Especially for road testing.

The fix?

Went to the junkyard yesterday and got an ECM from an '88 Olds 88
(Sounds like something from the department of redundancy department).
35$ plus tax, and now I've got an extra ECM to play with. Swapped the
Buick PROM and calpak into it and put it in the car. _Seems_ to be
better. Hard to tell at no load idle, but in drive with the air on it
seems much better. Half hour test drive around town in 90 degree plus
weather and across some speed bumps with no stalling or glitches. Am I
fooling myself with wishful thinking? Don't know. I'll let you all know
in a couple of weeks.

Sorry to run on so long, but I thought some of you might be interested.

Thanks again for all the responses. Great group!

Lynn

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      I may be stupid, but I ain't _that_ dumb.
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