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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Lss1six on March 03, 2018, 12:54:53 pm
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Hello everyone, just joined but I've have gotten a lot of information from this forum in the past. I've got my own little problem I can't figure out where to start. I did a little bit too much at once, but here's some background info. I've got an 88 r30 with 350 this, originally it had the th400 but I swapped it with a 700r4. While it was in the garage I rebuilt the throttle body, made the stock regulator adjustable and did the ultimate TBI mod. Now the truck runs like crap, its almost like a vacuum leak and I can hear an unusual sucking sound from the TB. I checked for external leaks with carb cleaner and found nothing. Put a fuel pressure gauge on after the filter and it was 18psi at idle and adjusting the regulator did nothing. It idles lower now too, like 500 rpm. Anyone have any ideas what it could be? Gotta get this figured out before I start messing with tv cable and trans governor for shift points.
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Welcome to the site
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Thanks Rapid Roy. Just an update, I found out I used the wrong tb base gasket, I used the one closed between the two bores instead of the open ones. Idles in park much better and sucking sound is gone. But in gear it still idles rough and also does it going down the road at light throttle. Haven't taken it past light throttle other then free rev in park.
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If the engine is basically stock, set the fuel pressure to 11-12 PSI. Verify the firing order, 1-8-4-3-6-5-7-2. Disconnect the EST bypass wire and verify that the ignition timing is set correctly. If the symptoms persist after all of that, unplug the vacuum line from the EGR solenoid to see if the symptoms clear up. Are there any DTC's stored in memory? When was the last tune-up performed?
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You're right, I'm going to check the basics, could of knocked timing off if I jacked the distributor against the firewall during the swap. It's not bad enough to be a miss though. No engine light is on, kind of hoping it would. Plugs cap, rotor, wires and filters are about a year old. I've got a question about measuring fuel pressure. Isn't the regulated fuel pressure only the section inside the TB before it goes to the injectors? I would think where I have it would just be whatever the pump is putting out.
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Fuel pressure throughout the entire length of the delivery line between the in-tank pump and the throttle body is managed by the regulator. Barring external leaks or physical damage to the fuel lines, the only components that will introduce variables are the fuel filter (if it becomes sufficiently restricted to limit fuel flow) and the tank selector valve (if it fails to fully transition between tanks), either of which can introduce a loss of downstream fuel pressure and starve the engine for fuel.
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does your CEL come on when you first turn the key on?
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Yes with key to the on position and engine not running the CEL is on
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Well for some odd reason I still have about 18psi fuel pressure. The tab on the regulator is in the same spot but why is my fuel pressure so high?
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What are you using to measure the fuel pressure?
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It's an actron 0-100 psi, went to auto zone to rent another to double check, but for some reason it doesn't have the internals to press on the shrader valve. I rechecked timing, cap, rotor, plugs, and wires, rebuilt TBI again along with regulator. Checked vacuum, 18-19 in hg at idle but drops to zero when revved. Steady throttle increase drops it but steadys back out never goes below 16. The only place I could read vacuum was the line going to map sensor. The ones out front for egr and canister did nothing even when I unplugged them while the engine was running. I don't think that's right. I also unplugged IAC and idle rose to 1500rpm and large sucking sound again.
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A 100 PSI gauge doesn't have the resolution to accurately measure a 15 PSI fuel circuit. You need to use the proper fuel pressure gauge.