Commin' through -- Hot fuel -- (was: -VAPOR LOCK-)

[mark grady]

Dave --

Interesting post about the Onan not liking warm/hot fuel. Couple of
questions:

1). The Howell system is a true blue GM TBI (throttle body injection) unit
isn't it?

2). What do you think the temperature of the fuel in the tank is with the
EFI (electronic fuel injection) system?

3). Do you feel that the warm fuel in the tank lead to more/faster
evaporation of the fuel? (Evaporative emissions)

4). Does Howell (or anyone else) make an MP/SFI system?
(multi point / sequential fuel injection)

There is a big difference in the performance and drivability between the
various GM systems. The SFI (non batch fire) systems are so much "snappier".

I also wonder if you (or anyone else) has done a comparison of what's out
there. EFI seems like a very worthwhile project. Would you care to share
your project costs?

Mark

mailto:mgrady

> -----Original Message-----
> From: owner-gmcmotorhome
> [mailtowner-gmcmotorhome]On Behalf Of Dave
> Sent: Wednesday, March 17, 1999 10:06 AM
> To: gmcmotorhome
> Subject: Re: GMC: Mexico ----VAPOR LOCK----
>
>

> >As soon as your state pollution laws will allow, go to an injector
> >system. They need the booster pump also.
>
> Two years ago I installed the TBI system from Howell. It was quite easy to
> install and worked first time. I had a few problems getting it to work
> right at very low power settings. It seems that the idle air bypass does
> not allow enough air to flow, especially during warm-up. The
> throttle plate
> is adjustable but thats not obvious from looking at the throttle body. I
> also have Thorley headers so I needed to switch the O2 sensor to a heated
> sensor. Thats a must when using headers. But the technical support from
> Howell was excellent and the TBI system makes my 455 start and run like
> brand new. I was even able to start using regular gas without the engine
> knocking. Something I could never do with the carb.
>
> But.... While the TBI system to works very well, I started having major
> problems with vapor lock on my Onan!
>
> The TBI system has a fuel return that is used to bleed off excess
> fuel flow
> and return it to the fuel tanks. The return flow is also used to keep the
> injectors cool. Unfortunately the fuel return heats up the remaining fuel
> in the fuel tanks. That is not a problem with the TBI due to the high
> pressure operation of the fuel system. But the Onan does not like
> being fed
> warm fuel.
>
> On hot days (over 90 degrees) the Onan would vapor lock after a couple
> hours operation on the road. I tried replacing the fuel pump (thinking it
> was bad). Then I moved the fuel pump out of the generator compartment and
> on to the frame rail. But it still vapor locked.
>
> The final solution was to add about 10 feet of 1/4" copper tubing between
> the fuel pickup in the fuel tank and the fuel pump. This allows
> the fuel to
> cool off enough that it will no longer vapor lock on hot days.
>
> It was not easy to figure this one out. So, if you install an injector
> system and start having problems with your generator, consider adding a
> cooling loop to the fuel pickup line before assuming that the generator
> fuel system has problems.
>
> Dave
> 73 Sequoia
>
> PS.
> I would be curious to find out if anyone else has had similar problems
> after installing an injection system or if I am just special...
>

 

[heinz wittenbecher]

>There is a big difference in the performance and drivability between the
>various GM systems. The SFI (non batch fire) systems are so much "snappier".
>

I just added the Variable Injection Controller to the Rance (Accel) EFI before leaving home.
Havn't actually tweaked it yet as I wanted to be sure all is still as it was before adding the VIC.
It'll allow controlling fuel to the individual injectors.

I'll report once I have formed an opinion.

Heinz
Wireless in Sacramento

 

[mr.c]

Can't add to the problem with the Onan, but I put in a Howell EFI, and I am
very happy with result. It starts and when I turn it off, it's off. No
lingering etc.
Al Chernoff

> Dave --
>
> Interesting post about the Onan not liking warm/hot fuel. Couple of
> questions:
>
> 1). The Howell system is a true blue GM TBI (throttle body injection) unit
> isn't it?
>
> 2). What do you think the temperature of the fuel in the tank is with the
> EFI (electronic fuel injection) system?
>
> 3). Do you feel that the warm fuel in the tank lead to more/faster
> evaporation of the fuel? (Evaporative emissions)
>
> 4). Does Howell (or anyone else) make an MP/SFI system?
> (multi point / sequential fuel injection)
>
> There is a big difference in the performance and drivability between the
> various GM systems. The SFI (non batch fire) systems are so much "snappier".
>
> I also wonder if you (or anyone else) has done a comparison of what's out
> there. EFI seems like a very worthwhile project. Would you care to share
> your project costs?
>
> Mark
>
> mailto:mgrady
>
> > -----Original Message-----
> > From: owner-gmcmotorhome
> > [mailtowner-gmcmotorhome]On Behalf Of Dave
> > Sent: Wednesday, March 17, 1999 10:06 AM
> > To: gmcmotorhome
> > Subject: Re: GMC: Mexico ----VAPOR LOCK----
> >
> >

> > >As soon as your state pollution laws will allow, go to an injector
> > >system. They need the booster pump also.
> >
> > Two years ago I installed the TBI system from Howell. It was quite easy to
> > install and worked first time. I had a few problems getting it to work
> > right at very low power settings. It seems that the idle air bypass does
> > not allow enough air to flow, especially during warm-up. The
> > throttle plate
> > is adjustable but thats not obvious from looking at the throttle body. I
> > also have Thorley headers so I needed to switch the O2 sensor to a heated
> > sensor. Thats a must when using headers. But the technical support from
> > Howell was excellent and the TBI system makes my 455 start and run like
> > brand new. I was even able to start using regular gas without the engine
> > knocking. Something I could never do with the carb.
> >
> > But.... While the TBI system to works very well, I started having major
> > problems with vapor lock on my Onan!
> >
> > The TBI system has a fuel return that is used to bleed off excess
> > fuel flow
> > and return it to the fuel tanks. The return flow is also used to keep the
> > injectors cool. Unfortunately the fuel return heats up the remaining fuel
> > in the fuel tanks. That is not a problem with the TBI due to the high
> > pressure operation of the fuel system. But the Onan does not like
> > being fed
> > warm fuel.
> >
> > On hot days (over 90 degrees) the Onan would vapor lock after a couple
> > hours operation on the road. I tried replacing the fuel pump (thinking it
> > was bad). Then I moved the fuel pump out of the generator compartment and
> > on to the frame rail. But it still vapor locked.
> >
> > The final solution was to add about 10 feet of 1/4" copper tubing between
> > the fuel pickup in the fuel tank and the fuel pump. This allows
> > the fuel to
> > cool off enough that it will no longer vapor lock on hot days.
> >
> > It was not easy to figure this one out. So, if you install an injector
> > system and start having problems with your generator, consider adding a
> > cooling loop to the fuel pickup line before assuming that the generator
> > fuel system has problems.
> >
> > Dave
> > 73 Sequoia
> >
> > PS.
> > I would be curious to find out if anyone else has had similar problems
> > after installing an injection system or if I am just special...
> >

 

[herm beeck]

"The TBI system has a fuel return that is used to bleed off excess
> > fuel flow
> > and return it to the fuel tanks. The return flow is also used to
keep the
> > injectors cool. Unfortunately the fuel return heats up the
remaining fuel
> > in the fuel tanks"

How does the TBI pressure regulator return heat up the fuel since the
return flow never enters the injectors. Are we talking about TBI or
Multi Port injection? Am I missing something? Help
Herm

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[dave1]

>1). The Howell system is a true blue GM TBI (throttle body injection) unit
>isn't it?

No, the TBI itself is an after market unit. I think its a holly. It may be
a direct replacement for a GM unit but I cant say for sure. The Fuel pump
is also an after market unit. The wire harness was made by Howell and the
rest (sensors and engine computer) are all GM parts. Off of an 80's 454
truck engine TBI system I think.

>2). What do you think the temperature of the fuel in the tank is with the
>EFI (electronic fuel injection) system?

Actually I did not measure it. But it is noticeably warm to the touch.

>3). Do you feel that the warm fuel in the tank lead to more/faster
>evaporation of the fuel? (Evaporative emissions)

I suspect that may happen. But I assume that the evaporative emissions
control system (I did not disconnect it) captures and burns whatever vapors
are produced. Actually my experience is that I get less fuel odor with the
TBI. One of the reasons I replaced the carb was the excessive gas fumes
coming from the carb after hot shutdown. That is not a problem with the
TBI. When you turn off the key, the fuel flow stops before the engine stops
turning. I would suspect that may even result in longer ring life given the
fact that there is no raw gas washing down the cylinder walls during shutdown.

>I also wonder if you (or anyone else) has done a comparison of what's out
>there. EFI seems like a very worthwhile project. Would you care to share
>your project costs?

I chose the Howell system mainly because its (mostly) based on stock GM
parts. I can get replacement parts just about anyplace that sells GM truck
parts.

>From a performance standpoint I could not ask for more. The idle is
perfectly smooth, acceleration is actually too good. With the headers and
the TBI I worry about breaking something from having too much torque. One
down side actually is that the throttle is a bit too sensitive for my
tastes. I like to baby the thing and with the TBI I find myself using much
more of the avalable power. Its a bit touchy when trying to park too. I
have been looking at ways to change the linkage to make it less sensitive
at low power settings but have not tried anything yet.

Dave
73 Sequoia

 

[mr.c]

> >1). The Howell system is a true blue GM TBI (throttle body injection) unit
> >isn't it?
>
> No, the TBI itself is an after market unit. I think its a holly. It may be
> a direct replacement for a GM unit but I cant say for sure. The Fuel pump
> is also an after market unit. The wire harness was made by Howell and the
> rest (sensors and engine computer) are all GM parts. Off of an 80's 454
> truck engine TBI system I think.

I bought the TBI from Howell. It is GMC computer from 83 to 89 thus about 20
years newer in technology. It uses all GMC parts except for the throttle body
which is holly and has two injectors in it.
Al Chernoff

>
>
> >2). What do you think the temperature of the fuel in the tank is with the
> >EFI (electronic fuel injection) system?

Fuel not used in the injectors is returned to the fill tube of the gas line, thus
go into the first fuel tank. I do not know the temp.
Al Chernoff

>
>
> Actually I did not measure it. But it is noticeably warm to the touch.
>
> >3). Do you feel that the warm fuel in the tank lead to more/faster
> >evaporation of the fuel? (Evaporative emissions)
>
> I suspect that may happen. But I assume that the evaporative emissions
> control system (I did not disconnect it) captures and burns whatever vapors
> are produced. Actually my experience is that I get less fuel odor with the
> TBI. One of the reasons I replaced the carb was the excessive gas fumes
> coming from the carb after hot shutdown. That is not a problem with the
> TBI. When you turn off the key, the fuel flow stops before the engine stops
> turning. I would suspect that may even result in longer ring life given the
> fact that there is no raw gas washing down the cylinder walls during shutdown.
>
> >I also wonder if you (or anyone else) has done a comparison of what's out
> >there. EFI seems like a very worthwhile project. Would you care to share
> >your project costs?
>
> I chose the Howell system mainly because its (mostly) based on stock GM
> parts. I can get replacement parts just about anyplace that sells GM truck
> parts.

I chose Howell as it was recommended to me and one that was compatiable with the
455 GMC. Easy to install. Cost about $1200 but that is complete with wiring
harness, sensors, very thorough instruction and testing manual, and injectors.
The nice thing about it is that you use the same Air Filter and do not have to
change the hatch cover.
Al Chernoff

>
>
> >From a performance standpoint I could not ask for more. The idle is
> perfectly smooth, acceleration is actually too good. With the headers and
> the TBI I worry about breaking something from having too much torque. One
> down side actually is that the throttle is a bit too sensitive for my
> tastes. I like to baby the thing and with the TBI I find myself using much
> more of the avalable power. Its a bit touchy when trying to park too. I
> have been looking at ways to change the linkage to make it less sensitive
> at low power settings but have not tried anything yet.

>From performance - Great. I was told that my carb was gone and could not be
rebuilt. Osburn tried twice and both times it failed after a few minutes. The
engine would keep running after I turned off the key, and I had to stop it in
gear. With the Howell, it starts righ away, and stops right away, no fuss no
bother.
Al Chernoff

>
>
> Dave
> 73 Sequoia