Christobal

Well I got back into diagnosing my problem. I can hear the fuel pump prime and the fuel pressure goes up to the 30-50 psi range intil I crank and start the engine. It runs smoothly but the fuel pressure falls. All this time I was assuming the fuel pump kept running. The last time my fuel pump went bad, it just quit, no function at all. My exhaust is very loud, basically open right now which makes it very hard to hear the pump. As the fp dropped into the 10 psi area and the engine began to stumble, there were quiet periods in which I noticed no fuel pump noise.

So just to make sure, I primed it then disconnected the fuel pump relay, confirmed there was no pump noise for priming when I turned the ignition on. Started the engine and got the same reaction out of the fuel pressure guage but no pump running whatsoever. Engine stalls after 10-15 seconds.

Oil pressure indicates normal in the 50 psi range while idling cold. What can cause the pump to shut down after priming and never start when the engine runs.

{{{{{{{{{I've heard talk in the past about some sort of oil pressure sender switch that if faulty will sense no oil pressure and shut the fuel pump off if the engine runs. If you think that's what it is, where is that switch? Got a part #? Don't have my book with me here.}}}}}}}}}

What else might it be? Any comments will be appreciated.

GMTech

You are exactly right, there is an oil pump switch designed as a saftey feature for your engine. It is on the rear of the block, behind the distributer. It is sometimes the same switch as the sender, somtimes they are seperate.

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Christobal

Alright thank you my man. Looks like we're on to something. Any more details from anyone? The car started life as an 88 GTA. One switch or two? If separate are there any defining details for the switch in question?

Thanks again

freeze92

My '89 GTA just has the one switch at the oil filter. There is a long pressure switch screwed into a boss just above the oil filter. This has the bypass for the fuel pump in it.

Christobal

OK, I've got my Tech2 mounted above where my distributer used to be. Pulled it off and found that pesky aluminum resevoir mounted on a 90 fitting and also having a one wire spade connector attached to it. The 90* fitting appears to screw into the manifold just a few inches towards the driver side from the distributer hole. This seems to be what GMTech was talking about, as there are no other obvious sensors sticking out back there and the bellhousing is immediately below the area. Problem is, I can't think of why

Freeze92 is describing a switch screwed in down near the oil filter. That seems like a more reasonable place to be tapping for oil pressure. haven't been under the car today but I seem to recall one or two sensors plugged in down by the filter.

Am I confused? Tell me so. Anyone want to break the tie? Either way, I'll contact Tustin Chevrolet tomorrow and see what they say.

Jim85IROC

iTrader: (2)

I wouldn't rule out your fuel pump just yet. For over a year my car ran fine, but wouldn't hold fuel pressure. If I hooked up a gauge and turned the key, the pressure shot up to 45 and bled off almost immediately. After a year, (2000 miles) the pump finally took a crap.

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Christobal

Sounds like your car kept running? Mine runs the same with the fp relay connected or disconnected after priming. The pump is definitely off when I crank or run the engine, but it seems to prime normally.

You're right though, I don't trust this fp. I should have put a Walbro in before. I'll do that, possibly before this one fails.

I'll get to work on the problem today. Looking into that switch first.

Vader

Christobal,

Perhaps this would help clarify the situation:



As you can see, you should be able to operate with the fuel pump relay completely removed from the vehicle.

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Vader
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Jim85IROC

iTrader: (2)

Vader, what year is that diagram from? In the last week I've spent a LOT of time staring at the diagram in my 85 Helm manual. My 85 is somewhat different, but what it boils down to is this:

The car WILL run with the FP relay disconnected because the oil pressure switch can back-feed the system. This condition will throw a code 54 and make for some serious cranking at startup because you have to crank until you get oil pressure before the car will start.

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<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
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freeze92

Vader has the right drawing. The fuel pump relay can be bypassed by the oil pressure switch in case the relay is to fail. When fuel pressure reaches about 7-10psi, the contacts in the pressure switch make to supply 12 volts to your fuel pump. Try this: First, connect a volt meter to check for 12 volts at terminal "A" on the fuel pump relay (tan and white wire) with the ignition on. Start the car and watch the voltage. Should stay between 11-15 volts. Check oil pressure. If normal, disconnect fuel pump relay - engine should continue to run. If it dies, then the oil pressure switch is bad. You may want to check voltage at the pump connector underneath the car also, just to eliminate a broke wire between there and the relay. If voltage stays above 11, then I would say the fuel pump is bad. One last.. when is the last time you replaced the fuel filter? Gas quality has dropped in the last few months, so I would also change that.

Christobal

Thanks to all.

Vader, thanks for that diagram, I either spin around a while or look at one of those when I feel like getting dizzy. Or beer. Beer and wine is even worse. Only try that at home. Seriously, thanks for that, I wish all wiring diagrams were that simple.

Yes, I have run the engine without the fp relay in the past as well. Everything is pointing to something relating to that switch. Picked a switch up just in case it's actually faulty.

fullsize fun

I know this thread is super old, but I have to clarify, the oil pressure switch is NOT a safety, its only wired like it is to keep the fuel pump on IF the relay fails, Don't believe me, start the car and unplug it, the engine will still run. all it does is bypass the relay.