Howell TBI

[bartz paul]

Jerry:

Who installed your TBI?

Do you know what year it was installed??

Does it have a knock sensor??

Paul Bartz

From: Jerry Hoxsey [mailto:jhoxsey]
Sent: Wednesday, October 27, 1999 1:42 AM

I have now plugged the unused holes in the adapter plate for the Howell TBI.
My vacuum at idle went from 17 to 19 and #2 and #3 cancel out as they
should. Next step is test drive. Hopefully today. Will report results.

Runs better now but still not all it should be. Found the wrong gasket
between the TBI adapter plate and intake manifold. It too was causing
vacuum leak. Replaced with correct gasket and no more leaks. Runs much
better now with no miss. Vacuum still pulls down on acceleration lower than
I like (4" or so) but Mr. C. says his does the same thing. Maybe that it
normal with TBI. Vacuum is about 12 on flat road at 60 mph. Guess I'll
live with it.

 

[bartz paul]

Manny:

Do you have the integrated knock sensor in your TBI system??

What year did you install yours??

Paul Bartz

From: MTrovao [mailto:MTrovao]
Sent: Wednesday, October 27, 1999 9:40 AM

Jerry, I also have the Howell setup and the vacuum stays up at the 18-20"
range at the 65/70mph range. Mine drops down in city traffic from putting
brakes on constantly.
You may still have vacuum leaks. At the time I was doing the installation, I
also replaced all the vacuum lines.
Very happy with mine.

 

[dave1]

I too have the Howell TBI system. I don't have the knock sensor option. My
vacuum readings are about 12-14 at 60 MPH flatland cruse. The vacuum
actually goes up a bit as my speed increases beyond 60. I have the OEM
final drive so I suspect that I am hitting the optimum part of the 455's
torque curve at the higher speeds.

I think what counts most is knowing wether or not your mixture is being
controlled properly. I was worried that I could damage my engine if it was
running too lean so I installed a Westach mixture gauge this summer. It
works great.

One thing that surprised me is how long the Howell TBI system takes to
"learn" the engine. When you first start running after having the battery
disconnected the mixture is all over the place. It swings way rich, way
lean, rich, lean as it hunts for the right injector duty cycle for your
speed and load. After about 2-3K miles it has learned the proper settings
for a wide range of speeds and loads and works quite well. Its also
surprising that, in spite of the wild mixture fluctuations (during the
learning curve) the engine still runs great.

The Howell TBI system is closed loop. It adjusts the fuel injectors and the
idle bypass air until the mixture fluctuates closely around 14.7. My guess
is that the TBI system will compensate for small vacuum leaks by adding
more fuel and passing less bypass air until the mixture is at the 14.7
target.

Unfortunately vacuum leaks usually do not effect all cylinders the same. So
its a good idea to find those pesky leaks if you can. A vacuum leak may
cause one or more cylinders to run leaner than the others. The TBI system
is reading the average mixture from four cylinders. If there is a vacuum
leak near one of those four, it will add fuel to get the average of the
four back up to 14.7 but the one cylinder seeing the vacuum leak will be
leaner than 14.7 and the rest will be richer.

Dave
Ann Arbor, MI.
73 Sequoia (26'/455/EFI/HEI)

 

[jerry hoxsey]

Date: Wed, 27 Oct 1999 10:50:54 -0400
From: Dave
Subject: Re: GMC: Howell TBI
I too have the Howell TBI system. I don't have the knock sensor option. My
vacuum readings are about 12-14 at 60 MPH flatland cruse.
The Howell TBI system is closed loop. It adjusts the fuel injectors and the
idle bypass air until the mixture fluctuates closely around 14.7

Dave,
That is the vacuum I expected and think I should have.
I installed a fuel/air ratio monitor I got from a fellow in Round Rock,
Texas that has I believe 11 leds that run from 12 to 17. I adjusted the
fuel pressure regulator on the TBI so that on level ground I run 14.7.
That seems to work great. In a pull it will go rich but settle right back
down when you level off.
The TBI system
is reading the average mixture from four cylinders. If there is a vacuum
leak near one of those four, it will add fuel to get the average of the
four back up to 14.7

I suspect if I can clean up any remaining vacuum leaks(replace all vacuum
lines) I will be looking pretty good.
Thanks a BUNCH for your input
Jerry

 

[bartz paul]

Manny:

Did you find the wiring harness specific for/to the GMC and every component
fit with adequate length of wire or did you either have to stretch things a
little or add additional wire length?

Where did you mount the computer? If other than in the engine compartment,
did you consider it (i. e. the engine compartment).

Did you get a listing of other than Howell (e. g. GM) part numbers for the
components?

Paul Bartz

From: MTrovao [mailto:MTrovao]
Sent: Wednesday, October 27, 1999 8:08 PM

In a message dated 10/27/99 7:03:53 AM Pacific Daylight Time,

>
No, I don't have the knock sensor option. I did the installation last year.

 

[bartz paul]

Manny:

Don't know if you noticed in one of my previous e-mails on this subject, but
Howell does offer an optional spark knock control, which in turn requires a
ECM, both for ~ $100.00.

Paul Bartz

From: MTrovao [mailto:MTrovao]
Sent: Thursday, October 28, 1999 11:35 AM

In a message dated 10/28/99 7:32:04 AM Pacific Daylight Time,

>
3) Not yet. The system is based on GM cars with the throttle body fuel
injection used on 87-89 cars, on 454's. Howell's system doesn't control
spark timing like the 87-89 GM engines, it relies on the tach signal from
the HEI for rpm input to the computer.
I did order some parts for spares.
Fuel pump
O2 sensor
Fuel filter

 

[al chernoff]

Manny, from my experiences, I recommend having an extra injector. I lost one
when I first installed it and one on the road. Might have been some
contamination in the lines, but I had to replace them and I carry an extra one.
al

> In a message dated 10/28/99 7:32:04 AM Pacific Daylight Time,

>
> fit with adequate length of wire or did you either have to stretch things a
> little or add additional wire length?
>
> 1) Yes I found the wiring harness to fit with adequate lengths. There was no
> need to add any wire length IF the components were installed whre Howell
> recommended.
> I wanted to have the "Service Engine Soon" light on the dash panel so I had
> to supply the wiring and light for that. Howell recommended it be mounted on
> the drivers side of the passenger seat.
>
> Where did you mount the computer? If other than in the engine compartment,
> did you consider it (i. e. the engine compartment).
>
> 2) I mounted the computer on the outside of the passenger seat base. I have
> the bench seat so its under the seat.
>
> Did you get a listing of other than Howell (e. g. GM) part numbers for the
> components? >>
>
> 3) Not yet. The system is based on GM cars with the throttle body fuel
> injection used on 87-89 cars, on 454's. Howell's system doesn't control spark
> timing like the 87-89 GM engines, it relies on the tach signal from the HEI
> for rpm input to the computer.
> I did order some parts for spares.
> Fuel pump
> O2 sensor
> Fuel filter
>
> Manny Trovao
> 73 Custom/ex-Glacier
> San Jose, California

 

[jerry hoxsey]

Date: Wed, 27 Oct 1999 23:06:38 EDT
From: Gcbr
Subject: Re: GMC: Howell TBI

I hope I am not going to get myself in trouble here but-----some thoughts.
Have you had the manifold magna-fluxed? Mine looked good after a good
bead blasting. Mine had two cracks causing both a vacuum leak and an
antifreeze leak. No wonder the sparkplugs were so many different colors.
Monday I happened to call Jim Bounds on another matter----during the
conversation I mentioned that my manifold had died. I am not sure
exactly what he said but I think it was "yeah they are starting to fall
like flies". Not trying to be a scare monger just trying to be helpful.

Take Care
Arch

Arch,
All my plugs look the same. Even the two that would not "CANCEL" look just
like the other six. I can detect no vacuum leak on the manifold with the
WD-40 spray test and I have no water leaks. So at this point I would have
to guess the manifold is OK.
Don't worry about being a "SCARE MONGER". GMC owners have nerves of
STEEL!!!!!
Thanks Arch
Jerry

 

[chuck blanford]

>All my plugs look the same. Even the two that would not "CANCEL" look
just
>like the other six. I can detect no vacuum leak on the manifold with the
>WD-40 spray test and I have no water leaks. So at this point I would have
>to guess the manifold is OK.


Jerry

What's the "WD-40 Spray Test"? That's a new one for me!

Chuck
77 K
North ID