PDA

View Full Version : Engine Coughs when I go faster....


David4MCSammyDuvall
05-05-2012, 07:46 PM
Need your help to figure out how to pinpoint the problem.....
I replaced the gas. Put a new fresh gas.
Poured the "gas treatment" in the tank.
Replaced the fuel filter.
The engine is still coughing when I drive my boat faster....
And I can smell the gas in the air.....
Does that means I need to replace the fuel pump ?!?
Or carburetor ?
My boat is 1995 MasterCraft ProStar 190 with a Corvette engine.
Your suggestions are appreciated.
Thanks.

JimN
05-05-2012, 09:56 PM
Need your help to figure out how to pinpoint the problem.....
I replaced the gas. Put a new fresh gas.
Poured the "gas treatment" in the tank.
Replaced the fuel filter.
The engine is still coughing when I drive my boat faster....
And I can smell the gas in the air.....
Does that means I need to replace the fuel pump ?!?
Or carburetor ?
My boat is 1995 MasterCraft ProStar 190 with a Corvette engine.
Your suggestions are appreciated.
Thanks.

First, you don't have a carb- you have a throttle body and each cylinder has its own injector. If you smell gas in the exhaust, check the coolant temperature sensor and scan for codes. If you see 14 or 15, replace it but I would check it first. The resistance should be in the 2K Ohm range is the air/coolant temperature is near 70 degrees. The one you want to check has two wires- one yellow and one black.

Here's a link to the temperature/resistance values-
http://shbox.com/1/4th_gen_tech2.html

If this checks OK, make sure the thermostats are good and the raw water impeller is good, the oil cooler is clear and you have good water flow through the cooling system.

David4MCSammyDuvall
05-09-2012, 02:16 PM
JimN...
No offense intended. I'm not following you. Can you explain what is causing my engine to "cough" when I tried to go faster ?
I suspect that it has something to do with the flow of the gas to the engine, since I can smell the gas in the air.
My boat runs just fine in the "Idle" speed. No coughing at all.
But when I go faster in about 40 mph, it started to cough.
Hope I explain it clear of the problem....
Thanks.

SilviaMan
05-09-2012, 02:24 PM
He is thinking your engine is over fueling, the coolant temp sensor helps control how much fuel your engine gets.
Information is king when diagnosing a problem. It costs nothing to check that part out and report back.
- Is your issue, on the very top end it coughs. Like you pull your hole shot and speed down the lake and when you get to 40 mph you have the problem?

David4MCSammyDuvall
05-09-2012, 03:54 PM
SilviaMan...
I get what you're saying....Thanks.
So my next question is... How do I check that part ? The coolant temp sensor ? Where is that ? I'm not a boat mechanic by all means.... But I'm enjoying learning how to fix my boat.
My favorite thing is a picture of the engine... with the instruction how to check... It helps me to understand because I don't have the "boat mechanic" language yet. Pretend that you're teaching a lady how to fix the boat engine. :-)

pmkkdx
05-09-2012, 04:31 PM
SilviaMan...
I get what you're saying....Thanks.
So my next question is... How do I check that part ? The coolant temp sensor ? Where is that ? I'm not a boat mechanic by all means.... But I'm enjoying learning how to fix my boat.
My favorite thing is a picture of the engine... with the instruction how to check... It helps me to understand because I don't have the "boat mechanic" language yet. Pretend that you're teaching a lady how to fix the boat engine. :-)

is she cute? :cool:

pmkkdx
05-09-2012, 04:31 PM
cause if not, she can call a mechanic :eek:

SilviaMan
05-09-2012, 04:58 PM
cause if not, she can call a mechanic :eek:

mmm. hmmm.

BoulderX45
05-09-2012, 05:03 PM
Spark Plugs....When was the last time you replaced the plugs? Gas smell? Maybe a issue with the plugs.....

Drodey
05-09-2012, 06:19 PM
I am with Boulder on this one...I have an 02 prostar that had similar issue. Changed the plugs and problem was solved. I hear that if the engine is not brought up to temp using fuel containing ethanol it can cause issues with the plugs. A fresh set solved my issue.

jakethebt
05-09-2012, 07:52 PM
Not that I want to question JimN as his engine knowledge has been second to none on this board for the most detailed engine work, but I thought the LT1 was multiport fuel injected and thus did not have a throttle body?

east tx skier
05-09-2012, 07:53 PM
I don't think all SD models had an LT1.

JimN
05-09-2012, 08:36 PM
JimN...
No offense intended. I'm not following you. Can you explain what is causing my engine to "cough" when I tried to go faster ?
I suspect that it has something to do with the flow of the gas to the engine, since I can smell the gas in the air.
My boat runs just fine in the "Idle" speed. No coughing at all.
But when I go faster in about 40 mph, it started to cough.
Hope I explain it clear of the problem....
Thanks.

What, exactly, have you checked, so far? Have you checked for codes? Do that. Check the fuel pressure. The vast majority of driveability issues are caused by bad fuel pressure, fuel quality, clogged/dirty fuel filters, etc. You should have an anti-siphon valve at the tank and if this is clogged/gummed up, it will restrict the flow. You may have two fuel filters- one at the top of the tank and one on the engine. The one at the tank is right next to the anti-siphon valve and if this has never been changed, you're well overdue.

However, if the engine is running rich, it's usually not a fuel pressure issue.

I don't remember seeing which engine you have- is it the TBI or LT-1?

If the engine is getting too much fuel, it could be the ECT which, as mentioned would make the ECM think the engine is really cold and at low temps, it needs more fuel to achieve the correct fuel/air mixture but it's not the only thing that affects the fuel delivery.

If you want to diagnose this engine, you'll need some tools, or access to them- a multi-meter, a fuel pressure gauge with a purge valve, various wrenches and a few specialty tools, like a feeler gauge for checking the spark plug gap.

Old plugs will have a wider gap and won't deliver spark that is intense enough to burn all of the fuel. Old plug wires will do the same thing.

JimN
05-09-2012, 08:37 PM
Not that I want to question JimN as his engine knowledge has been second to none on this board for the most detailed engine work, but I thought the LT1 was multiport fuel injected and thus did not have a throttle body?

The piece where the throttle plate is located is the throttle body.

SkiDog
05-09-2012, 09:35 PM
I had somewhat of the same problem if ya'll remember. But mine is a carbed motor, not injected. I replaced all the filters, and that didn't fix the problem. When I changed out the fuel line from the tank to the pump, THAT fixed the problem.:):):)

jakethebt
05-09-2012, 09:38 PM
His post states corvette engine, which I believe is a LT1.

jakethebt
05-09-2012, 09:38 PM
The piece where the throttle plate is located is the throttle body.

Thanks! Learn something everyday.

boxman3
05-09-2012, 10:11 PM
Check your advance on your distributor - older models have a weight kit that manually advances... the kit will have replacement spring....

JimN
05-10-2012, 05:07 AM
Check your advance on your distributor - older models have a weight kit that manually advances... the kit will have replacement spring....

There's no distributor on an LT-1- it has a star wheel on the crank with crank sensors to tell the IC Module (Ignition Control) when it should produce spark and the ECM which direction/how fast the crank is turning. Also, the injected engines on MC never had centrifugal or vacuum advance.

RyanD121
05-14-2012, 11:27 AM
Not to question any of the previous responses, its obvious you guys know your sh!t, but what are your RPM's when you get to 40mph? What prop are you running? What elevation are you at? Could it be possible your boat is incorrectly propped and your "cough" is nothing more than your engine hitting the rev limiter? Keep in mind I have no experience with this engine, only an MCX and LY-6. Just a thought, don't kill me if I'm way off base...