 Another fuel pressure question, Diagnosis help please |
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| boiledcabbage |
 Sep 4 2012, 03:17 PM
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#1
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Member  Group: Members Posts: 50 Joined: 23-May 05 From: Ottawa, Canada Member No.: 4,131  |
Tracking a performance problem on my stock 74 1.8 FI and would appreciate any thoughts:
Sluggish in 3rd and above and wondering if fuel is the issue. starts and idles well,good compression, recent tuneup and valve adjustment although I did it myself... 32psi at idle, 29psi at 3000rpm measured at the CSV, volume only 1.0 liter perminute, no visible kinks or bundle in the tank. Any thoughts? I will be double checking the vacuum advance and timing just in case... |
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| underthetire |
Sep 4 2012, 03:25 PM
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#2
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914 Guru Group: Members Posts: 5,062 Joined: 7-October 08 From: Brentwood Member No.: 9,623 Region Association: Northern California |
And check the mechanical advance as well.
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| Dave_Darling |
Sep 4 2012, 04:26 PM
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#3
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914 Idiot Group: Members Posts: 15,161 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California 
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One liter per MINUTE? That sounds like a seriously deficient volume. Or did you mean one liter per SECOND?
--DD |
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| boiledcabbage |
Sep 4 2012, 04:30 PM
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#4
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Member Group: Members Posts: 50 Joined: 23-May 05 From: Ottawa, Canada Member No.: 4,131 |
Thanks Dave -no I really did mean 0.5l in 30 seconds - although that is just using the arm to run the pump ie maybe my battery is a bit low? -but what about a steady 29
Psi? Would that still provide adequate fuel? Do you think a restricted fuel one could provide both enough pressure but limited volume? |
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| SLITS |
Sep 4 2012, 04:53 PM
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#5
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"This Utah shit is HARSH!" Group: Benefactors Posts: 13,602 Joined: 22-February 04 From: SoCal Mountains ... Member No.: 1,696 Region Association: None  |
Spec is 50 - 62 L/hr .... 0.83 - 1.03 L/min .... based on your measurement, you are well within the required specification for volume.
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| boiledcabbage |
Sep 4 2012, 05:08 PM
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#6
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Member Group: Members Posts: 50 Joined: 23-May 05 From: Ottawa, Canada Member No.: 4,131 |
QUOTE(SLITS @ Sep 4 2012, 02:53 PM)  Spec is 50 - 62 L/hr .... 0.83 - 1.03 L/min .... based on your measurement, you are well within the required specification for volume. Thanks for the spec SLITS - I'll start to look elsewhere eg distributor advance for the problem |
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| Dave_Darling |
Sep 4 2012, 08:24 PM
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#7
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914 Idiot Group: Members Posts: 15,161 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California
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Crap, I had the units wrong! Thanks for checking on that, Slits. I would have steered him completely wrong.
--DD |
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| Mike Bellis |
Sep 4 2012, 09:04 PM
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#8
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Resident Electrician Group: Members Posts: 8,347 Joined: 22-June 09 From: Midlothian TX Member No.: 10,496 Region Association: None 
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I once had a fuel filter with a blockage that would only manifest above 3000rpm. When I pulled it apart, I found a large aluminum burr left over from the manufacturing process. As the volume of fuel increased, it would push the burr into the outlet and block the flow. Took me forever to find it.
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| pilothyer |
Sep 4 2012, 09:39 PM
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#9
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Member Group: Members Posts: 838 Joined: 21-May 08 From: N. Alabama Member No.: 9,080 Region Association: South East States |
Although your fuel pressure regulator seems to be in spec, you may want to test it several times to be sure it doesn't have a diaphragm leak....warm up the engine with the fuel pressure gauge connected.........at idle (high vacuum) the FPR should maintain about 28 psi.....pull the vacuum connection (simulating under load condition) and the pressure should rise to about 35 psi.... reconnect the vacuum to FPR and the pressure should again fall to about 28 psi............when you remove the vacuum source from the FPR plug it with your thumb because any vacuum leaks will cause problems.
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| boiledcabbage |
Sep 6 2012, 05:51 PM
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#10
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Member Group: Members Posts: 50 Joined: 23-May 05 From: Ottawa, Canada Member No.: 4,131 |
QUOTE(pilothyer @ Sep 4 2012, 07:39 PM) Although your fuel pressure regulator seems to be in spec, you may want to test it several times to be sure it doesn't have a diaphragm leak....warm up the engine with the fuel pressure gauge connected.........at idle (high vacuum) the FPR should maintain about 28 psi.....pull the vacuum connection (simulating under load condition) and the pressure should rise to about 35 psi.... reconnect the vacuum to FPR and the pressure should again fall to about 28 psi............when you remove the vacuum source from the FPR plug it with your thumb because any vacuum leaks will cause problems. Thanks pilothyer (and others for your help) I had not thought to check the pressure with and without vacuum on the FPR -I'll see what happens..... |
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