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View Full Version : 94 TBI 350 injector cutting under load.


André
05-23-2012, 10:34 PM
Hey guys!
Boat run great for 4-5 passes through the course then bog around 1600-1800 rpm.
Being a TBI,i can clearly see the passenger side injector completely cutting out and starting back to inject when i pull back the throttle.
I checked visually the wiring and connectors and decided to swap the right and left injectors connectors.The trouble followed the connector and around the same rpms,the driver side injector stopped working,coming back on as i pulled back on the throttle.
Idle is fine.Fuel pressure,lines,pick up and filter are fine.
If the wiring or connection of the injector wasn't good,i think it would bug at idle too but it's injecting fine at idle and instantly stop injecting when it happens.
Any ideas and help is welcome on what to check next.Will double check the wiring and connections tomorrow morning first thing(I took the A.M. off to check this out.Priorities first!The boat,then work!)
T.I.A.
André

jmhjgh
05-23-2012, 10:48 PM
I do not have an answer for you, but mine is doing the same thing. It will start surging at about 3000 rpm and you can see the injectors cutting out. My engine runs perfect up to 3000 rpm. I had access to a marine scan tool and everything looks good and with no engine codes.

Have you tried spraying a can of starter fluid or similar down the throat while it is happening? If it gets better, it would point to a fuel problem. On mine, the aerosol did not change the behavior. I was going to check the rubber exhaust hoses to make sure they were not collapsing on the inside, but it is strangely repeatable w or w/o load.

j.mccreight@hotmail.com
05-23-2012, 10:51 PM
Hey guys!
Boat run great for 4-5 passes through the course then bog around 1600-1800 rpm.
Being a TBI,i can clearly see the passenger side injector completely cutting out and starting back to inject when i pull back the throttle.
I checked visually the wiring and connectors and decided to swap the right and left injectors connectors.The trouble followed the connector and around the same rpms,the driver side injector stopped working,coming back on as i pulled back on the throttle.
Idle is fine.Fuel pressure,lines,pick up and filter are fine.
If the wiring or connection of the injector wasn't good,i think it would bug at idle too but it's injecting fine at idle and instantly stop injecting when it happens.
Any ideas and help is welcome on what to check next.Will double check the wiring and connections tomorrow morning first thing(I took the A.M. off to check this out.Priorities first!The boat,then work!)
T.I.A.
André

heres a tbi diag wiring diagram

Double D
05-23-2012, 10:56 PM
I had a similar problem but mine was during idle. It would surge up and down after being used 25+ minutes. Mine ended being one of the injector drivers on the computer board. My computer would need to be replaced if both drivers were bad but the computer was set up to run a 4 barrel and I only have a 2 barrel, so the dealer combined my two injectors on one driver. Been working now for over a year. If it does it again, its a new computer.... :(

André
05-23-2012, 11:02 PM
So one injector works properly in either location? I think you alrerady found the problem, you swapped injectors and the problem followed to the other side so you know the wiring is good on both sides so no need to check that, all you need in a new injector, they can fail in numerous ways ...

Sorry,something can get lost in translation when i talk technical stuff.
I swapped the connectors not the injectors themselves.The problem followed the connector.
The passenger side that was cutting at first was now running good and the driver side injector was now cutting out completely around 1800 rpms.
Clear as mud?:)

Double D
05-23-2012, 11:09 PM
Sorry,something can get lost in translation when i talk technical stuff.
I swapped the connectors not the injectors themselves.The problem followed the connector.
The passenger side that was cutting at first was now running good and the driver side injector was now cutting out completely around 1800 rpms.
Clear as mud?:)

Mine did the same thing, followed the connection at the computer. Sounds like a driver in the computer. If you, or your mechanic, can combine the two injectors, it should work for you.

j.mccreight@hotmail.com
05-23-2012, 11:09 PM
I misread your post originally, thats why i did the edit thing, i agree with double d its prolly in the ecm you are going to need to hook up a dvom on those pins for the injectors and see if it is losing the ground signal when the boat acts up. it might a little difficult as the ecm is pulsing the ground to fire the injector, but if the injector stops squirting all together then it should not be there, i gave you a diagram for your diag.

André
05-23-2012, 11:13 PM
I had a similar problem but mine was during idle. It would surge up and down after being used 25+ minutes. Mine ended being one of the injector drivers on the computer board. My computer would need to be replaced if both drivers were bad but the computer was set up to run a 4 barrel and I only have a 2 barrel, so the dealer combined my two injectors on one driver. Been working now for over a year. If it does it again, its a new computer.... :(

Interresting.I was thinking something similar tonite if it turns out to be the ECM.(Yes,i'm a hacker and cheap!)Any ideas how he did that? Just jumped the wires together at the injectors?
Thanks for the help and ideas guys!

JimN
05-23-2012, 11:16 PM
Hey guys!
Boat run great for 4-5 passes through the course then bog around 1600-1800 rpm.
Being a TBI,i can clearly see the passenger side injector completely cutting out and starting back to inject when i pull back the throttle.
I checked visually the wiring and connectors and decided to swap the right and left injectors connectors.The trouble followed the connector and around the same rpms,the driver side injector stopped working,coming back on as i pulled back on the throttle.
Idle is fine.Fuel pressure,lines,pick up and filter are fine.
If the wiring or connection of the injector wasn't good,i think it would bug at idle too but it's injecting fine at idle and instantly stop injecting when it happens.
Any ideas and help is welcome on what to check next.Will double check the wiring and connections tomorrow morning first thing(I took the A.M. off to check this out.Priorities first!The boat,then work!)
T.I.A.
André

Does it only do this when you try to accelerate hard, or can you increase throttle slowly and get it to rev higher?

Unplug the TPS and see if this changes. It will be sluggish and you may see a code/trouble light but go ahead and rev it. If it seems to be OK, check the TPS with a multi-meter set for continuity. If you see the meter react suddenly as you move the throttle, it would seem that the TPS has a problem.

j.mccreight@hotmail.com
05-23-2012, 11:18 PM
yes all you need to do is to connect both signal wires from the ecm, but the hard part is knowing which driver in the ecm is bad

JimN
05-23-2012, 11:18 PM
Interresting.I was thinking something similar tonite if it turns out to be the ECM.(Yes,i'm a hacker and cheap!)Any ideas how he did that? Just jumped the wires together at the injectors?
Thanks for the help and ideas guys!

The ECM only has one set of output leads for each injector, so I don't know how the dealer did this. These harnesses are made specifically for the application and don't have a second set of injector outputs.

Double D
05-23-2012, 11:20 PM
Interresting.I was thinking something similar tonite if it turns out to be the ECM.(Yes,i'm a hacker and cheap!)Any ideas how he did that? Just jumped the wires together at the injectors?
Thanks for the help and ideas guys!

Sorry to say, I am not sure how they did it.

André
05-23-2012, 11:33 PM
Does it only do this when you try to accelerate hard, or can you increase throttle slowly and get it to rev higher?

Unplug the TPS and see if this changes. It will be sluggish and you may see a code/trouble light but go ahead and rev it. If it seems to be OK, check the TPS with a multi-meter set for continuity. If you see the meter react suddenly as you move the throttle, it would seem that the TPS has a problem.

Both.
Will try this tomorrow morning.Would a faulty TPS stop only one injector completely dry?
Thanks for the help guys!

JimN
05-24-2012, 12:22 AM
Both.
Will try this tomorrow morning.Would a faulty TPS stop only one injector completely dry?
Thanks for the help guys!

I was thinking in terms of acceleration enrichment/deceleration enleanment as a TPS problem. Whether it makes one injector shut off is determined by the actual problem.

I think I would start the engine and wiggle the main harness on the engine, especially near the coolant temperature sensor.

André
05-24-2012, 09:22 AM
I was thinking in terms of acceleration enrichment/deceleration enleanment as a TPS problem. Whether it makes one injector shut off is determined by the actual problem.

I think I would start the engine and wiggle the main harness on the engine, especially near the coolant temperature sensor.
Will try the famous wiggle the wires trick too!
Thanks Jim!

André
05-24-2012, 11:02 AM
Is there anything between the ECM driver signal and the injectors?
Wires turned out fine between the J2 connector and the injector connector.
Also measured the resistance of the TP sensor,3k to 8k ohms,very linear.
Very windy here,don't know if i'll be able to do some on water testing...

André
05-28-2012, 05:23 PM
Update.
Recheck all the wiring,measured resistance of the wires while whiggling the wires and connectors,didn't find nothing wrong so i went skiing with all my tools in the boat.
We did 20 passes plus a couple more start because of fallen skiers and the engine didn't skip a beat,just like it ran for the last 900 hrs of use.:confused::confused::confused:
The wiring diagram show a ground wire for the injectors on my TBI.
Anyone knows where it is cause there's only 2 wires going to the injectors itself...
Thanks for your time!
André

André
06-05-2012, 05:55 PM
7-8 sets of skiing and all is good.Don't know why but the boat is running like it always did,perfectly!Knock on wood...
Thanks to everyone for the help and specially James who took time to talk to me on the phone about troobleshoothing my problem!
Have a great summer!
André

PineLakeRumble
02-28-2014, 12:09 PM
Greetings Andre,

I will be looking at a 94MC with the 350TBI not far from you. How have you found this engine as far as strength and reliability over the years? The engine has approx. 800hrs on it and seems to be well looked after. Anything I should be aware of? If I decide to purchase, this will be my first experience with fuel injection in a boat. Any tips/suggestions for a prospective buyer?

Cheers.

PineLakeRumble
02-28-2014, 12:25 PM
For those who like pictures...

Bouyhead
02-28-2014, 02:27 PM
The Iron Duke of small blocks!! Put a ton of hours on mine without any issues. Not the most efficient injection system by todays standards but a great motor.

PineLakeRumble
02-28-2014, 05:28 PM
Better throttle response / fuel economy than a Holley 4160?