Fuel problems - Team Camaro Tech
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post #1 of 10 (permalink) Old Feb 21st, 03, 01:36 PM Thread Starter
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Greetings all,

I have here an interesting situation (at least to me it is). I have been having a problem with my car on cold starts but hadn't really had much time lately to mess with it. Well today I had a little time and was feeling frisky. The car is an 1989 iroc-z with the 350 tpi stock. anyway, I did what the service manual tells you to do in their diagnostic chart. Came to the part where you put the fuel pressure gage on the rail and check for pressure, turned ignition on without starting and pressure went to 47. It then dropped to 40 for about 10 seconds and then slowly dropped over a period of about one minute to 18 psi where it stayed. Now here is where it gets interesting! Before I was about to go tearing the plenum off and checking for a leaking injector, I decided to pinch off the fuel return line and check for a possible leaking fuel pressure regulator. After I pinched off the return line, I turned the ignition on without starting and surprise, no pressure. Turned ignition off, removed the clamp and did the igniton thing again. I had pressure this time. Was positive that I had pinched off the return line, went back to the service manual and checked it, looked at the lines, re-checked the book and sure enough. I had pinched off what was supposed to be the fuel return line but must have been crossed with the pressure line somewhere before I bought the car. My question is this, is it possible for the car to run with the lines crossed like this or do I have a gremlin following me around?

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post #2 of 10 (permalink) Old Feb 21st, 03, 01:47 PM
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Hmmmm, those 2 hoses have different size fittings so that can't happen.

How does it run at operating temp?

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post #3 of 10 (permalink) Old Feb 21st, 03, 02:02 PM Thread Starter
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[img]graemlins/clonk.gif[/img] thanks for your reply back ZZ430DropTop67RS. How about if the hose connections are swapped back at the fuel tank?

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post #4 of 10 (permalink) Old Feb 21st, 03, 03:53 PM
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[checkedcalanderforaprilfirst/]
That's a strange one for sure...seems like there would have to be a restriction in the "new" return line to build pressure???

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post #5 of 10 (permalink) Old Feb 21st, 03, 04:16 PM Thread Starter
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Hey Bill,

If the lines are reversed Like they appear to be. The restriction in the line would be the fuel filter since this is an in-tank electric pump and as long as the pump is running you would have some pressure in the line. I plan to get under the car tomorrow and check the routing from the tank to the fuel rail. My question was, "is it possible for the engine to start and run with the lines reversed". At present time it takes about six tries before the car will start and even then it wants to cut off. This is a new fuel pressure regulator that was put on there recently.


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post #6 of 10 (permalink) Old Feb 21st, 03, 04:27 PM
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No, the engine would not start and run even if somebody did the unlikely swapping of these 2 lines.

Sounds to me like it's going to need the pump.

[ 02-22-2003, 07:42 AM: Message edited by: ZZ430DropTop67RS ]
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post #7 of 10 (permalink) Old Feb 21st, 03, 07:47 PM
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I don't know for certain about GM, but some auto manufacturers ECUs won't engage the fuel pump with every twist of the key. I think it has something to do with the ECU not detecting crankshaft pulses on an attempt and shuts the fuel pump off to prevent flooding. Just want to keep you aware that you may be getting side tracked by a completely unrelated issue. Keep working on your diagnostic for now. Check crank and cam sensors (if provided). For cold start, I'd be suspicious of the intake air temp sensor.

-dnult

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post #8 of 10 (permalink) Old Feb 21st, 03, 09:04 PM
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Hmmmm..

Q "is it possible for the engine to start and run with the lines reversed".

A Even though the first two pressure readings look OK from the 2 second pump run when the ign was turned to the on position (gremlins?), there are no pressure readings given during cranking or while it is trying to run...not enough info ....

But...If pressure stays present (40-47lbs), My thoughts are that the injectors don't have a clue or care how the pressure got to the fuel rail, so yes...it should run...

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post #9 of 10 (permalink) Old Feb 22nd, 03, 04:39 AM
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It's true that the injectors don't know the difference, since pressure is equal in all directions.

But, since it's impossible to reverse those 2 lines, we're just discussing theory now.

If somebody managed to make 2 adapters to do this, the pressurized fuel would be routed through a small "5/16" line, unfiltered to the rail.

I'm wondering how long the engine would run on this volume of unfiltered fuel.

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post #10 of 10 (permalink) Old Feb 22nd, 03, 08:44 AM Thread Starter
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[img]graemlins/clonk.gif[/img] [img]graemlins/clonk.gif[/img] [img]redface.gif[/img] [img]graemlins/clonk.gif[/img]

Okay, now that I have finished bashing myself. I would like to thank everyone who responded for their comments. The mystery of this whole mess has been solved. First off, as ZZ430DropTop67RS mentioned in his post, it is physically impossible to reverse the lines at the fuel rail or anywhere in the engine compartment. However it is possible to reverse them back at the fuel tank by using oversize hoses and clamps. Fortunately, this is not what happened. After tracing the fuel lines from the tank to the engine, looking at a friends car and comparing it to mine, here is what I found. Previous owner replaced the fuel lines and routed them in reverse order. Next there is a bracket to hold the fuel lines where they connect to the flex hoses. The original bracket here had been replaced with a fabricated (can we say jury-rigged) one in which the lines had been installed in reverse order because of the way the lines were routed. This is what led me to come up with the conclusion and question that I did.
Now back to the problem that started this whole mess, losing fuel pressure at the rail. This is what I found by disconnecting both the pressure and return flex hoses one at a time. I have a good clean fuel flow thru the pressure hose and clean fuel leaking back thru the return hose as the pressure slowly dropped off. I have not had any fuel residue on any of my spark plugs and even though I recently replaced the fuel pressure regulator with one from a brand X parts store, this would appear to be the culprit here. Either that or the fuel pressure regulator housing on the rail is worn inside. Either way, I am replacing the regulator either with a standard one from the dealer or an adjustable one and will also check the housing real good. Sorry to be so long winded on this post, must be related to a politician. [img]redface.gif[/img]

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