| [GMCnet] Fuel Pressure Question [message #182456] |
Thu, 30 August 2012 18:39  |
Tim Conway
Messages: 412
Registered: September 2005
Location: Long Island, New York
Karma: 0
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I received this email from a GMCer this morning...
>>> At the tail end of the day yesterday, my fuel pressure started doing wacky things. It didn't seem to affect the performance, but the pressure - which should be around 15 to 18 PSI would climb to over 40! Not sure what's causing that. I don't even know what controls the fuel pressure. I don't have a pressure regulator AFAIK, so I guess I'll get one and pop it in.
Have you read/heard anything about a TBI fuel injection system having intermittent high fuel pressure like that? <<<
Thanks for any ideas, thoughts or suggestions...
Tim Conway
LI NY 78 PB
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| Re: [GMCnet] Fuel Pressure Question [message #182458 is a reply to message #182456] |
Thu, 30 August 2012 18:54  |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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There are only a few possibilities...
1) The fuel pressure regulator is bad (if he's not got an external one, there's almost certainly one in the throttle body)
2) The return line from the fuel pressure regulator (wherever it is) is plugged (without a return line, the pressure will ramp up to whatever the fuel pump can supply)
3) The gauge he's using to measure fuel pressure is flaky. He may or may not notice any "problems" with the way the coach runs with high fuel pressure, since the system will self-regulate to keep the fuel/air mixture correct.
If he could give us some info on what style / manufacturer of throttle body and "system" he's using, it might help.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] Fuel Pressure Question [message #182459 is a reply to message #182456] |
Thu, 30 August 2012 19:02 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Tim,
If he's not having any engine operating problem, the pressure is probably
not varying as much as he thinks. He does have a regulator, probably built
into the throttle body.
The first question is, "how do you know it's jumping?" I suspect he has an
electrical fuel pressure gauge with a resistance type pressure sender. As
I've reported several times, those are inherently prone to rapid failure
when subjected to erratic fuel pressure -- as most fuel systems seem to
experience. There's no way to repair a failed sender. When he replaces
it, he may want to install a "snubber" ahead of it. Here's the one I
recently installed before my sender -- I have no idea whether it's adequate
to protect the sender long term: McMaster-Carr 4034K1.
Oh yeah, tell him to join us at GMCMH-EFI & he'll hear all that stuff. :-)
https://sites.google.com/site/gmcmhefi/home?pli=1
Ken H.
On Thu, Aug 30, 2012 at 7:39 PM, Tim Conway wrote:
> I received this email from a GMCer this morning...
>
>
> >>> At the tail end of the day yesterday, my fuel pressure started doing
> wacky things. It didn't seem to affect the performance, but the pressure -
> which should be around 15 to 18 PSI would climb to over 40! Not sure
> what's causing that. I don't even know what controls the fuel pressure. I
> don't have a pressure regulator AFAIK, so I guess I'll get one and pop it
> in.
>
> Have you read/heard anything about a TBI fuel injection system having
> intermittent high fuel pressure like that? <<<
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Fuel Pressure Question [message #182463 is a reply to message #182459] |
Thu, 30 August 2012 19:17 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Senior Member |
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I'll second Ken's suggestion. I've gotten a TON of great and useful data as I put my own Howell / junkyard system together.
Just today, based on input from the GMCMH-EFI group, I picked up the computer-controlled distributor (wow was that a pain to extract), a water temperature sending unit, a MAP sensor, some odds and ends bracketry, and even an air box that might solve my ram air system design problems (off a '91 TBI Caprice - if it works, I'll post the details).
But until yesterday I was suffering from the perception that fuel pressure changes would affect the TBI fuel/air mixture, until informed by one of the GMCMH-EFI members that the ECM will adjust around those changes in fuel pressure, at least until it's way out of bounds, or too low.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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