Stumped on VP 5.7 GI....

[Johnhhi]

I have a 2002 VP 5.7 gi, fuel injected.
It will start only when I pump the throttle rapidly and then it will only stay running at 1500 rpm or higher. When it is running it surges +/- 500 rpm. No idle. It also pops randomly through the throttle body. The timing has been set and adjusted. (many times). The injectors were removed and refurbished. I checked the injectors when hooked up to the engine and they are only opening when I pump the throttle rapidly, tps is new, and the injectors are working correctly. It seems like the signal for the injectors to open is intermittent. There was a problem with the wiring harness having bad wires, it has been replaced. I also removed the heads and had the top end rebuilt. Here is a list of what has been replaced;

Throttle position sensor
crank position sensor
cam position sensor
distributor cap and rotor
ignition control module
coil
temp sending unit
wiring harness
fuel pump assembly
all filters
anti syphon valve
starter
heads rebuilt / all gaskets for top end
plugs
pick-up in fuel tank checked and clear

I'm stumped at this point, any help would be appreciated......

 

[Johnhhi]

Re: Stumped on VP 5.7 GI....

...a couple more things, I also replaced the fuel pressure regulator and I had a fuel pressure gauge hooked up during all of this, pressure is great after the new fuel pump. I also tried running the engine off of a portable tank, no change...

 

[Don S]

Re: Stumped on VP 5.7 GI....

Hook it up to a scan tool and see what it's doing while running. And what is the full model number of your engine, not just the year, or the serial number.

 

[Johnhhi]

Re: Stumped on VP 5.7 GI....

its a 5.7GI-E, I don't have access to a scan tool and the boat is 2 hours away. I'm trying to get a game plan together for the next trip. Anybody know a place I can send my ECM to have it tested??

 

[Don S]

Re: Stumped on VP 5.7 GI....

The ECM is tested on the boat with a scan tool. You have already thrown more parts at it in hopes of fixing it that what a scan tool would cost. http://www.rinda.com/marine/mtspec.htm#techmate

 

[Don S]

Re: Stumped on VP 5.7 GI....

Why were the heads rebuilt? Did the engine have this problem before all the work started?

 

[Johnhhi]

Re: Stumped on VP 5.7 GI....

first, I didn't throw in parts hoping it would fix the problem. We tested the sensors and parts with multimeters and fuel gauges etc. and replaced them accordingly..... http://easyautodiagnostics.com/index_gm_4.3L_5.0L_5.7/index_of_articles_1.php

Don, the engine didn't have this problem before the heads were done, the valves had corroded from a faulty riser gasket allowing water to seep into the manifolds. I think the problem started from the wiring harness having bad/ broken wires and corrosion under the insulation at some of the connections. (at the cam sensor and the icm just before the plug the wire under the insulation was all but gone). of course when I removed the heads the wiring harness was moved all around and I think thats where my problems started. Also whoever had the boat last had stripped and twisted the wires for the fuel pump together and taped them back into the harness, When I found that I decided it was time to just replace the harness.
I've seen on other posts here that the ECM can be sent out to be tested and re-programmed at a fraction of the cost of a scan tool but no links on where to go

 

[Don S]

Re: Stumped on VP 5.7 GI....

Since the heads were put back on, have you done a compression test? If not, I would sure do one now.

 

[Johnhhi]

Re: Stumped on VP 5.7 GI....

Yes, compression is 140 +/- 5lbs on all

 

[Johnhhi]

Re: Stumped on VP 5.7 GI....

I'm convinced its an issue with a bad signal to the injectors, with them out of the intake and hooked to the fuel/harness they only fire when I throw the throttle back and forth. All the signs of a throttle position sensor but its good, tested the new one to make sure it wasn't bad. Its sending a great signal.
....Is it bad when you start picturing your boat at the bottom???

 

[gbeltran]

Re: Stumped on VP 5.7 GI....

I'd also be checking for vacuum leaks.

 

[Tail_Gunner]

Re: Stumped on VP 5.7 GI....

There is a serial number or product number on you ecm module post it. Have you checked and cleaned the IAC circut...But the fact that you worked with the wiring harness is alarming in the sense that wires just dont corrode that badly by themselves...what part of the harness did you rewire....spefically did you wire the ecm input or output's????

Here's a WAG when you pump the throttle does that mean the command at the steering wheel or the linkage on the throttle body...IF its the steering wheel command you may have a faulty kill switch and the rapid movement is allowing the switch to make continutiy...Hmm you need a spark plug test light and see if your ignition circut is being interuppted...no spark no fuel

A diag tool would make this very easy..you have a old system that is going to need some future attention...

 

[Johnhhi]

Re: Stumped on VP 5.7 GI....

the iac tested good, didn't replace it. I pumped the throttle at the throttle body with the cable disconnected. the kill switch is good (by passed it temporarily). Spark is good and constant. The only thing not constant is the injectors opening. I just cant make the connection between pumping the throttle and them working on and off while I do it. Seems to me the ECU would not work at all if it were bad. I replaced the harness with a new one after I found the bad wiring, the bad wires were to cam sending unit, icm, and the fuel pump

 

[Tail_Gunner]

Re: Stumped on VP 5.7 GI....

http://www.mdmotors.ru/netcat_files...akteristiki_sistem__EFI__MEFI__MPI__alb_2.pdf

Not questioning you at all but how do you know the spark is constant i would visually watch it fire with a light if the ignition circut is interupted that will cut off the injector's..shut them down.

Unplug the IAC run the engine is it the same.

Here is possibilty..what is the voltage at closed throttle 0 or 0.5

Throttle Position (TP) Sensor
4 The Throttle Position (TP) sensor is a potentiometer connected to
the throttle shaft on the throttle body. The TP sensor has one end connected
to 5 volts from the ECM and the other to ECM ground. A third
wire is connected to the ECM to measure the voltage from the TP sensor.
As the throttle valve angle is changed, the voltage output of the TP
sensor also changes.
At a closed throttle position, the voltage output of the TP sensor is low
(approximately 0.5 volts). As the throttle valve opens, the output increases
so that at wide open throttle the output voltage should be near 5 volts.
The TP sensor has a feature to aid start-up of a flooded engine. Advance
the throttle approximately 3/4 of the way, and crank the engine.
The TP sensor will send a zero (0) volt signal to the ECM, and upon
receipt of this signal, all injector operation will stop. Once the flooded
engine starts, ECM / TP sensor operation returns to normal.
By monitoring the output voltage from the TP sensor, the ECM can determine
fuel delivery based on throttle valve angle (operator demand). A
broken or loose TP sensor can cause intermittent bursts of fuel from the
injector and an unstable idle.
If the TP sensor circuit is open, the ECM will set a DTC 21 or 22. Once a
DTC is set, the ECM will calibrate a default value for the throttle position
and some engine performance will return.
Intake Air Temperature (IAT) Sensor