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#1
03-07-2018, 02:18 PM
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fuel starvation
A friend is fighting an issue w/a 70 GTO where the engine will sputter as soon as the secondaries are tipped in.All of the normal items have been tried including but not limited to adding a 70 gph electric pump. The only thing that made a difference was after pulling the fuel pickup out to check the condition of the "sock" and reinstalling made it slightly delay the sputter. Is it possible that there is a particular orientation of the "sock"/pickup that is being missed? It will pull strong to 5200 in low on the primaries but as soon as the secondaries are tipped it sputters like lack of fuel. It has done this w/ the original Q-Jet and one prepped by Jet Performance. Ignition has been gone over including but not limited to trying different modules.
Thanks for any suggestions |
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#2
03-07-2018, 02:27 PM
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I would suggest pulling the sock off. What brand of pump? A 70gph is pretty weak. Is the pump at the back or the front and how is it wired? A temporary fuel pressure gauge would show any pressure drop at WOT.
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 466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
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#3
03-07-2018, 04:45 PM
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It kinda sounds like the secondary air valve is opening too fast. How is the secondary air valve spring adjusted?
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'78 Macho T/A DKM#95, 460cid, SRP pistons, KRE 310 D ports, 3" pypes, Hooker 1 3/4" headers, hydraulic roller, 10" Continental, 3.42 gears 11.5 @117.5mph 3900lbs  ([_|_] ##\|/##[_|_]) |
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#4
03-07-2018, 05:21 PM
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I know it's a pain to do but you really need to go ahead and put a fuel pressure gauge at the carb inlet. It's the only definitive way to know if it's a fuel starvation issue or not. I don't think it's ignition or a secondary valve issue based on what you're describing, but a gauge reading will take all the guesswork away. Let us know the results.
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62' Lemans, Nostalgia Super Stock, 541 CI, IA2 block, billet 4.5" crank, Ross, Wide port Edelbrocks, Gustram intake, 2 4150 style BLP carbs, 2.10 Turbo 400, 9" w/4:30 gears, 8.76 @153, 3100lbs |
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#5
05-16-2018, 05:59 PM
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unreal update
My friend got the GTO back in the shop and chased the "fuel starvation" symptom one more time w/a previously installed fuel sending unit (made in china) appearing to seal off p/u tube when installed. Corrected angle of tube, no help. Decided problem must be something internal in engine. What was found was: previous shop had replaced rear main seal w/engine removed. Offered to clean & paint while out of vehicle. For whatever reason, painted engine w/intake off, oil pan off, valley cover off, valve covers off. Proceeded to paint WITHOUT MASKING ANYTHING. Of course, paint didn't stick to oily internal surfaces, collected on oil pump p/u screen, kept pressure but lost volume to point, lifters were not completely pumped up, making cam work as a much smaller version (decreased lift & duration). Also starved rod bearings to point just short of failure. Good news is that previous shop agreed to pay for proper repairs.
Just posted in case anyone was curious what was found and the fact that the real problem was so weird. |
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