99 5.7 Penta WOT issue

[duststang]

Just purchased this boat (99 5.7 Penta TBI) took it out ran good no issues, full throttle over 5000RPM. This weekend took it out and at WOT it bogs cannot get past 4200RPM's. I can run it at 4200RPM's 3/4 throttle with no problems (I ran it 4200 for 30 mins) but soon as I WOT it bogs? The boat starts ok cranks for a couple sec and starts, idles good smooth. When I take the boat out of the water there is black soot on the back like it is running rich? ? I just had the exhaust bellow replaced.The boat sat for 2 years prior to me purchasing it. I am now wondering if it could be bad fuel, water in fuel or should I just start throwing parts at it? Anyone ever had this issue?

 

[dypcdiver]

Re: 99 5.7 Penta WOT issue

First find out what the problem is before throwing money at it. Do simple cheap checks like plugs, Dist cap, rotor arm, check for water in the fuel filter etc. Sounds as if the problem might a fuel issue if it has sat for 2 years. You might want to think about running it for a test on a known good supply straight out of a can of new fuel to eliminate the tank supply.

 

[duststang]

Re: 99 5.7 Penta WOT issue

replaced dist cap, rotor, fuel filter, air breather, and plugs. Put Seafoam in gas then took it out yesterday and it still bogs WOT. I noticed all the plugs had a lot of gas and #3 was more black than the rest. The back of the boat still had black on it like it is running rich. Is it common for a TBI to get gum up?

 

[Boobie Trap]

Re: 99 5.7 Penta WOT issue

replaced dist cap, rotor, fuel filter, air breather, and plugs. Put Seafoam in gas then took it out yesterday and it still bogs WOT. I noticed all the plugs had a lot of gas and #3 was more black than the rest. The back of the boat still had black on it like it is running rich. Is it common for a TBI to get gum up?

Look for my thread "Can't get over 3000 RPM out of both engines."

I found out that the engines were being fuel starved. Replaced the high pressure fuel pumps, they were clogged up, and now both engines run better than they ever have.
Fuel pumps on a volvo are simplistic to change!! One nut and a screw and you are done!

Hope it helps!

 

[duststang]

Re: 99 5.7 Penta WOT issue

Look for my thread "Can't get over 3000 RPM out of both engines."

I found out that the engines were being fuel starved. Replaced the high pressure fuel pumps, they were clogged up, and now both engines run better than they ever have.
Fuel pumps on a volvo are simplistic to change!! One nut and a screw and you are done!

Hope it helps!

My boat seems to be running rich (black on back of boat and plugs were coated in gas).This lead me to believe that fuel pump was suppling enough fuel. I maybe wrong? I am now thinking maybe I have a bad injector or clog dumping in the fuel does that sound logical?

 

[Don S]

Re: 99 5.7 Penta WOT issue

You need to get it hooked up to a diagnostic computer and see what the running temp is showing. If the ECT sender is saying the engine coolant is cold, the ECM will run in a rich condition, and when warm will cause a problem.
It won't set a code, because all it sees is a cold engine. Your temp gauge may show your engine is running at 175? but the ECM may be told by the ECT that it's only 100?.

 

[duststang]

Re: 99 5.7 Penta WOT issue

Here are some helpful video's incase someone might have similiar issues.. changing the temp sensor today thanks for the advice I will report back what happend.
chevy tbi rebuild and injector testing - YouTube
Chevy Tbi running rich problem solving - YouTube
How to check your Chevy TBI spray pattern - YouTube

 

[duststang]

Re: 99 5.7 Penta WOT issue

ok so timing is set at 8 deg at 1,000 RPM, MAP is 4.7volt @ 0vac/3.6v@5vac/2.8v@10vac/1.9v@15vac/1v@20vac/.5v@25vac, TPS is .5volts @ closed/3.95v @ WOT, Fuel is 30 psi on/30psi idle/ 30 psi rev/ under load?, fuel pressure on reservoir 0psi?, anyone know if the TPS voltage sounds low @WOT? can low fuel pressure make rich condition? the spark plugs are fouled and running like crap. any advice is appreciated...

 

[duststang]

Re: 99 5.7 Penta WOT issue

took it to a marine shop and they did not tell me why it is running rich but they said I have a dead #3 cylinder and will most likely need a new motor $5,000. So the price seems high but wouldn't I still be running rich since all the plugs are fouling out current motor.

 

[duststang]

Re: 99 5.7 Penta WOT issue

took heads off and head gasket between 3-5 cylinder and the #3 exhaust valve bad. oh well drop the heads off at machine shop should be ready in a few days. then I can get back to figuring out the rich issue.

 

[dlk4602]

Re: 99 5.7 Penta WOT issue

I would be interested in what you find out about the rich issue. I have the same motor and I think mine is running a bit rich also.

 

[duststang]

Re: 99 5.7 Penta WOT issue

ok update, after I took the heads off I noticed cylinder was beat up and few bad valves. It appears that this thing has gotten extremely hot. I also noticed all the gaskets are Felpro which tells me someone has had this engine apart before. I pulled the engine and ended up bore it .030, new pistons, bearings, seals, polished crank, .015 mill heads, new valves, seals, etc ($1,200 parts & labor). Before I put the engine back in I started checking everything because never found the root cause. I noticed that one of the exhaust flappers was missing but it was on the opposite side of blown head gasket. I removed the Y pipe and guess what I found a flapper totally blocking the exhaust and it has been this way for a long time because it was melted and stuck so bad I barley could pry it out. Hopefully when I put this new motor back in I will not have a rich issue?

 

[jimmbo]

Re: 99 5.7 Penta WOT issue

When the flapper was choking the exhaust the engine was probably running with a lower than normal intake manifold vaccumn which resulted in a richer mixture than needed. With the restriction gone the engine operating paramaters should return to normal

 

[duststang]

Re: 99 5.7 Penta WOT issue

When the flapper was choking the exhaust the engine was probably running with a lower than normal intake manifold vaccumn which resulted in a richer mixture than needed. With the restriction gone the engine operating paramaters should return to normal

that is what I am hoping...

 

[duststang]

Re: 99 5.7 Penta WOT issue

ok so started right up purr like a kitten with 40psi oil pressure set timing at 8deg BTDC and so smooth. I noticed my fuel pump is whining really loud so guess I am going to replace them. When I am finished everything will be new exhaust manifolds, risers, starter, fresh water pump, etc. "should be reliable". I ran it for a while and did not seem to be running rich so I think the blocked exhaust was the culprit. I am going to check the plugs today to make sure they are not fouled.

 

[duststang]

Re: 99 5.7 Penta WOT issue

put it on the water yesterday it runs great about 57 speed at 4700RPM with 3 guys. Had good oil pressure and never above 175 degree. bore .030 over and mill heads .015 seems to have better power. thanks everyone for helpful information this forum is awesome.