Idiot needs help!!! 2001 5.7 GXI-B TBI

buyrbware

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Jun 27, 2019
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Figured title might get some results much needed. I am a decent mechanic but getting old and forgetful. Here is my problem, I put my boat in the water (2001 Larson cabrio 254) last month and noticed that I couldnt get over 4000 rpm I also noticed a high pitch whine from the fuel pump. I changed the fuel cell after being towed back to the dock. I used a after market pump package and new filter. All lines are clear and tight. Boat idles all day at 600 rpm. Once you advance throttle engine will hold a rpm for a few seconds then fall back to idle. It then starts to surge from idle to where you have the control lever set at. Example 1800 RPM. Will surge back and forth and TBI sounds like it is sucking a lot of air. Doesnt make that sound till it starts to surge. If i return the control lever to idle shut the engine off and restart it will idle at 600 again all day long. once you advance the throttle it will start surging sometimes so bad it stalls. Items replaced so far in the last 30 days.
1. fuel cell hi low pumps
2. Injectors (qty 2)
3. distributor cap and rotor
4. plugs
Items cleaned
1. IAC looked good
2. fuel regulator internal to TBI holds pressure.

This sounds like it is starving for fuel once you advance the throttle will occasionally backfire too. Fuel pattern from injectors looks even and very good strength and spray pattern. I want to check the new fuel cell pressures but cant find fittings to attach to the volvo low and high pump ports (still looking). I would appreciate any help given. the boat has 375 hours on it and I have owned it for 5 years and never had issues. Ideas??????
 

alldodge

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Need to measure your fuel pressure. Place it inline at the TB

GM TBI adapter.jpg
 

buyrbware

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Jun 27, 2019
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I will pick this up and place it inline to get the reading. I am told low pump should be 8-14 and high should be 30-40 is that correct. If I have proper pump psi any ideas what is next I basically replaced the fuel system at that point.
 

QBhoy

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“IAC looked good” would be where I would start. Best of luck.
 

cptbill

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Probably should get someone to put a scanner on it so you know what's working and what isn't
 

buyrbware

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Update: Finally read pump pressure and have 30psi at all times off of high pump, Idle is fantastic and holds 600 all day long. Replaced the ignition control module in the distributor also. When the boat is throttled up in neutral it proceeds to climb in RPM when I select a RPM I.E. 1500 it will hold for a few seconds then fall back to idle. It will not hold the rpm that I set with the control lever, however if I keep my hand on the throttle as it starts to fall back to idle I can bump the lever and the RPMs will return and climb higher. I did find a loose then disconnected ground wire on my high pressure pump. I have repaired that but still have a response in the throttle that falls back to idle. I guess the next step is to put a scanner on it.
 

Saline Marina

Petty Officer 2nd Class
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Sep 9, 2014
Messages
162
On a GM TBI truck engine there's also a MAP manifold absolute pressure sensor and a TPS throttle position sensor.

Those are integral to the ECM calling out the proper injector pulsewidth.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Update: Finally read pump pressure and have 30psi at all times off of high pump, Idle is fantastic and holds 600 all day long. Replaced the ignition control module in the distributor also. When the boat is throttled up in neutral it proceeds to climb in RPM when I select a RPM I.E. 1500 it will hold for a few seconds then fall back to idle. It will not hold the rpm that I set with the control lever, however if I keep my hand on the throttle as it starts to fall back to idle I can bump the lever and the RPMs will return and climb higher. I did find a loose then disconnected ground wire on my high pressure pump. I have repaired that but still have a response in the throttle that falls back to idle. I guess the next step is to put a scanner on it.

the throttle on the TBI unit is connected to the helm control via cable.

have you verified that the throttle at the TBI unit isnt physically moving?

maybe check both ends of the cable to make sure they are still attached.
 

alldodge

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Thanks for the fuel pressure, we know this isn't the issue

Need a scanner attached to see what the MAP, TPS and IAC are doing, and if there are any codes.
 
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