Chevy 454 with Throttle Body Injection
Betti Ann & Preston Smith
a 454 cid engine and Throttle Body Injection. Since January,
I have been plagued with what seems to be an intermittent
fuel feed problem that has cost me in excess of US$700 with
no resolution.
The general symptom is that the engine will suddenly start
to surge to the point that the on board computer goes into
'limp' mode. On most occasions it seems to clear itself.
Consequently when I am on the road and make it to a repair
facility the diagnostics show nothing.
The best example of what happens is that in February while
traveling from Savannah to St. Mary's, the engine began
surging with a total loss of power. The computer did not go
into limp mode. After having been rejected by the Chev and
GM dealers in Brunswick GA (would not work on motor homes) I
made it into Brunswick Tire, Brake and Alignment Center,
4262 Norwich St., Brunswick GA (recommended by the Chev
dealer) where the manager (Jeff) was a smart mechanic who
enjoyed working on motor homes. He was able to run through
the complete computer diagnostic scenario while the engine
was misbehaving. All diagnostic tests and results came back
with normal readings in spite of the engine misbehaving
while under diagnosis. In frustration, he went into the
books for about 20 min, grabbed a wrench, and hit the Fuel
Flow Regulator. Lo and behold!! The engine began to purr
like a kitten. We also changed the fuel filter (I can only
find one) in spite of having changed it just two weeks
prior. We added enough fuel injector cleaner for the 75 gal
tank and ran that through the system. Until recently we
have only had one reoccurrence of the problem and a tap on
the regulator and another dose of injector cleaner cleared
the problem. As an aside, i bought the rig in October from
a chap in Fredericton NB who ran a fleet of trucks and used
his own very, very capable mechanic to look after the
chassis. The owner was a NASCAR groupie who trekked yearly
into the US to attend Daytona and two or three other races.
So the possibility of old fuel gumming up the works is not
really viable.
After returning home from Florida in mid April, I parked the
rig and started it from time to time as I did some
maintenance. This past week i tried to start the engine and
it would not fire. In spite of turning rapidly, nothing
happened. After talking to a local mechanic, we sort of
concluded that the problem is fuel related especially since
as i turn the engine the butterflies remain dry. Yesterday,
while poking and prodding and rubbing my chin, I turned the
key and away it went (the butterflies, of course, were damp
from fuel). As I watched, it stuttered, stumbled, surged
and eventually died (butterflies were now dry). No amount
of turning, cussing or hitting the fuel flow regulator with
a wrench would get it to start again.
On Monday, I will replace the filter to rule it out (and
will also hit the inlet side on a piece of white paper to
see if anything of significant size has been trapped by the
filter.
My questions are:
0) Does my diagnosis make sense?
1) Is there a place on the web where i can find some info on
how a throttle Body injection works or can someone give me a
quick walk through of its theory of operation and the role
the fuel flow regulator playa?
2) Could these symptoms indicate a bad fuel pump?
3) Can the Fuel Flow regulator be
repaired/cleaned/rebuilt? Does the P Series maint manual
address this?
4) Are there CD versions of the P37 or 454 or TBI
maintenance manuals available or web sites that might have
some info on these items?
5) Does the Chevy P series maintenance manuals address the
P37 chassis. I ask this because Helm talks about the
P-series chassis manual and an RV chassis manual (with the
Suburban and Jimmy)?
6) Does anyone have a used copy of the 91 chassis manual
that they no longer need and are willing to sell?
7) Are there one or more FAQs that might compile 454 info
contained in Motor home, Trailer Life, and like magazines?
8) Where else can i find info?
Thanks for all of the help
Preston
W F Sill
>I have a 91 Fleetwood Cambria on a 91 Chevy P37 chassis with
>a 454 cid engine and Throttle Body Injection. Since January,
>I have been plagued with what seems to be an intermittent
>fuel feed problem that has cost me in excess of US$700 with
>no resolution.
Preston, your description strongly suggests you should replace the
fuel flow regulator. Very few mechanical devices are repaired
permanently by whacking them with a wrench!
Will KD3XR ---- the Curmudgeon of Sill Hill
"When I was a boy, I was told that anybody could become president;
I'm beginning to believe it."
C. Darrow
Ross Binnie
I too have the same chassis albeit a 1994 and the diagnostics are a bit
better. Even so, fuel problems can drive you nuts. The Helm manuals are
first class and cover all known problems at time of publication. Also there
are service notes covering many problems not identified in the original
manual. You can read the index at Helm's web site.
The TBI pulse control system can be read by the GM diagnostic tool. This is
not displayed in the trouble code output so it may be the mechanic who
worked on your chassis was not able to see the whole picture. With the "OBD
II" diagnostic tool, actual TBI operating paprameters are displayed in real
time. The level of information provided by the "OBD II" is limited to some
extent by the model year of your chassis -:).
In brief, the TBI injectors are controled by the engine controler. Input
information is provided by different elements such as MAP (manifold absolute
pressure) TPS (throttle position sensor) oxygen sensor and vehicle speed
sensor. The output is a 'Pulse Modulated' signal to the injectors. This
determines how long the injector remains 'ON'.
Fuel pressure must be present for the injectors to work.
I realise the agony you are going through. From my perspective, i suggest
you find a GM truck dealer in NB (Moncton ?) who has the latest diagnostic
equipment. Check and make sure he also has the P series service manual for
your model or else buy your own (I did). Take a test drive with the
equipment connected. It stores transient faults as well as trouble codes.
The fuel pump is a costly item to replace. Some mechs claaim it is simpler
to just install an inline fuel pump. I am not sure that this will work (if
it is the pump) as normal inline pumps work at lower pressures than that
required for GM TBI systems.
I know! dropping the tank on your rig is a real pain and costly too. Thats
why I suggest a GM truck dealer. Visit them and get a feel for how they
opperate. Truck dealers are a bit different than car dealers (although the
service areas are not as clean -:) )
Happy Trails?
Betti Ann & Preston Smith wrote in message <392FDBC3...@navnet.net>...
>I have a 91 Fleetwood Cambria on a 91 Chevy P37 chassis with
>a 454 cid engine and Throttle Body Injection. Since January,
>I have been plagued with what seems to be an intermittent
>fuel feed problem that has cost me in excess of US$700 with
>no resolution.
>
Betti Ann & Preston Smith
Yes the questions do roll from this Canuck's mouth.
Yesterday I chatted with the service manager at the local GM
shop. I was about to replace the fuel flow regulator but he
suggested that it might also be the ignition chip that is
with the distributor. he also told me how to extract the
codes from the on board computer.
He said to jumper the A and B terminal on the diagnostic
plug and watch the service needed light for the two digit
codes which will each flash 3 times. The first code will be
12 which is the handshake code. Then any uncleared fault
codes will show up - 42 for the ignition chip and 32 for the
EGR valve.
Armed with this new found knowledge i made a jumper for the
diagnostic plug, turned on the ignition key and shoved the
jumper in. As I did this i was called to the phone -
automatically i turned off the ignition. When i returned I
just turned the ignition on again. Oh, Oh!! the jumper was
still in place and with a Pfffttt all went dead. Now there
is no juice going to anything that is connected to the
chassis battery - ignition, lights, horn, etc. all gone.
So i obviously have shorted something out. I have not had a
chance to look closely at all of the fuse yet but since
everything is dead there must be a fuse, relay, or fusible
link that protects the whole shebang. A cursory look at the
fuse panel does not show such a 'master' fuse device. Any
ideas?
I have looked at helm for a manual for my rig and the only
one i see that might apply to my 91 P37 chassis is for a
Suburban/Jimmy/R/V (R/V is the way Helm spells RV. is that
the way yours is packaged? I also have not been able to
find the manual indices you refer to -
can you point me in the right direction?
Thanks for your help
Preston
Larry Scholes
I have a 1990 Southwind with the 454 TBI and experienced a loss of power
similar to what you describe. The problem ended up being the oxygen sensor.
It may not be your cure but it's inexpensive enough and easily installed to
try. And if it hasn't been replaced in a while, it's probably due.
Good luck.
larry.
"Betti Ann & Preston Smith" <prs...@navnet.net> wrote in message
news:392FDBC3...@navnet.net...
Dave Tobias
I have a fishing yacht with twin 454 crusaders. They are the marine version of what you have. They are TBI with the fuel return loop same as your RV. There are differences but the theory of operation is the same. If you think you have an issue with the fuel pressure (meaning fuel pump and or fuel pressure regulator), don't guess!! It is trivial and cheap to buy a fuel pressure tester! Your TBI will have a spec for fuel pressure. My marine unit is 17 PSI but yours could be lower. My crusaders have fuel pressure test ports with schrader valves but if yours does not have this then they make adapters which go inline. This is how you diagnose fuel issues! If your fuel pump is weak, your fuel pressure will fluctuate. If your fuel pressure regulator inside your TBI body is bad then you will likely have low pressure, but too high of pressure is a problem as well and it could be from a blockage on the return side. By default, the pump is able to deliver some speced volume with no restriction and some pressure with complete restriction on the output. IF you put a partial restriction on the output then you will get some reduced flow at some increased pressure. This is how the pressure regulator creates pressure, it restricts the output. So you can actually test your pump by clamping off the return fuel line and observing the pressure that the pump is able to create. Your TBI unit DEMANDS proper pressure as a base condition. This is because the injectors are nothing but a solenoid with a given orifice size. The controller knows that if it opens the orifice for 1.5ms (for example) that it will be delivering X amount of fuel. It knows what the intake airflow characteristics of the engine are either using a mass air flow sensor OR simply because of the design of the engine. Example, a 454 has so much cylinder volume and if it is going 1000 RPMs then the computer knows how much air it is sucking in. It needs to add fuel so that the proper ratio of air to fuel is maintained. If your fuel pressure is above spec then each millisecond of open time for your injectors will inject too much gas and it will run rich. IF your fuel pressure is too low then each ms of open time will deliver less fuel than expected and you will run lean. If your fuel pump relay is cutting out for whatever reason (and there are some reasons the ECM will do this on purpose like crash detection and low oil pressure detection), then this will show up as low/uneven fuel pressure. So I cannot emphasize enough that you need the ability to monitor fuel pressure, know what the spec is, and understand the symptoms you will see if it is too low or too high.