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tcseward
06-29-2009, 07:58 PM
I Have a 95 PS 205 with the 350 TBI engine. The engine bogs down around 2800 RPM's. It drops by about 500 RPMs. I have changed the fuel filter, cleaned the screen on the fuel pump, cleaned the screen on the tank pickup, changed the throttle position sensor, changed the MAP sensor, and run the trouble codes (no codes). I have not checked the fuel pressure because there is not a pressure test port on the system. I think it is electrical because when I disconnect the throttle sensor or the MAP sensor the engine revs up just fine. could it be the knock sensor detecting a knock and retarding the timing? the engine will will continue to rev up after it losses RMP, but it seems like the timing get retarded.

If anybody knows of a way to test the fuel pressure please let me know so i can rule that out. I also think it could be a vacuum issue. Is the only vacuum line the one from the TB to the MAP sensor? This line looks fine.

Thanks in advance for all of your help.

Chris

JimN
06-29-2009, 08:59 PM
I Have a 95 PS 205 with the 350 TBI engine. The engine bogs down around 2800 RPM's. It drops by about 500 RPMs. I have changed the fuel filter, cleaned the screen on the fuel pump, cleaned the screen on the tank pickup, changed the throttle position sensor, changed the MAP sensor, and run the trouble codes (no codes). I have not checked the fuel pressure because there is not a pressure test port on the system. I think it is electrical because when I disconnect the throttle sensor or the MAP sensor the engine revs up just fine. could it be the knock sensor detecting a knock and retarding the timing? the engine will will continue to rev up after it losses RMP, but it seems like the timing get retarded.

If anybody knows of a way to test the fuel pressure please let me know so i can rule that out. I also think it could be a vacuum issue. Is the only vacuum line the one from the TB to the MAP sensor? This line looks fine.

Thanks in advance for all of your help.

Chris

You already replaced too many parts. If the MAP sensor or TPS were bad, you would have seen the check engine light come on and it would store a code. ANy time you unplug one of these sensors, the ECM will default to a pre-determined value. If the TPS is off, it defaults to 12% throttle and since the MAP sensor runs the show above 2% throttle, it's no real problem unless the throttle has moved quickly, more than +/- 20%. If the MAP sensor is off, it'll accelerate like a stove but either way, it will throw a code. If the knock sensor is picking up knock or no signal at all, it'll throw one of two codes. If it's picking up knock, it pulls the advance back in 5 increments until it reaches base timing. If you want to verify the KS operation, connect a timing light and start the motor. Let it warm up a bit and increase the RPM. You should see the timing advance as you go. I definitely won't say the KS isn't bad- the ceramic fitting where the lead attaches broke off for no apparent reason, although it could have been snow or slush that caused it. If you don't see the timing advance, rev it up and watch the timing mark as you hit one of the motor mounts with a hammer. It should briefly retard the timing.

What is the idle speed? It should be 600RPM. If it's higher, make sure you don't have a vacuum leak, like from the PCV valve hose, MAP sensor hose or at the base of the throttle body.

Verify that the base timing is at 10BTDC. To set/check this, you need to go to the ALDL (Data Link Connector) at the rear of the motor. If you have a scan tool, use that but if you don't, you can use a paper clip, inserted in positions A and B. Attach the timing light's pickup to the #1 plug wire and start the motor. You'll need to manually maintain 1000RPM for this. If you can get a timing light with a dial for the advance, it's much easier- all you need to do is set the timing light's advance to 10 and look for is the timing mark to line up with 0. Once that's set (or verified), tighten the clamp at the distributor base and re-check (it can move).

The best way to check the fuel pressure, since your fuel line doesn't have the Shrader valve, is probably going to involve taking the hard fuel line to a shop that does fuel system repairs, so a valve can be installed. You don't want to cut the line and splice one in with rubber line- it's the high pressure side and that's not allowed, approved or smart. Once the valve is in, you'll be set. For the life of me, I don't know why they didn't include this on the first injected motors, other than the fact that it eliminated boat owners from messing with things when these were new to the lineup.

Go to the tank and look at the aluminum part where the fuel line attaches. Look for a small lever on an aluminum fitting. If that's not aligned with the fuel line, turn it so it is. That's the fuel shutoff valve and they occasionally move over time. If this was already aligned, remove the fuel line and then remove the barbed fitting. It should have a ball in it, with no schmutz around it and it should move freely when you press on the ball. Make sure this is clean. Once everything is clean and the line is still off of the barbed fitting at the tank, remove the fuel line from the pump inlet and somehow blow air into the line from one end to the other. If there's any resistance, find out why. In some cases, the fuel tank rests on the line and it can collapse, restricting the flow. In a few cases, the fuel line de-laminated internally and it's like a blister- this can also restrict the flow. You should be able to blow air into the pickup tube and with the line off of the pump, it should be very free of back pressure.

Have you looked at the injector's spray pattern? It should be a solid cone with no voids. If it has voids, your injector(s) need(s) cleaning.

If you have a vacuum pump, you can plug the port on the throttle body base and attach the pump to the line that goes to the MAP sensor. Increase the vacuum while the motor is running and you should notice a change. If you carefully back-probe the MAP sensor's plug (never pierce the insulation- use pins and slide them past the green silicone rubber seals), you can measure the voltage on the blue wire, reference the black terminal to the ground at the rear of the motor and see the variation on the third wire (IIRC, gray). The blue wire should be at about 4.5VDC, the black should have no more than .1 Ohms to the ECM ground and the range of the gray wire should be about .7VDC-4.5VDC.

tcseward
06-29-2009, 10:08 PM
Jim thank for your help. one thing jumped out at me with your post. My boat idles at 650 to 700 RPMs. Am I looking at a vacuum leak probably? I took of the throttle body today and cleaned it. I am going to pick up a new gasket in the morning. It doesn't seem like a fuel problem to me because the motor will continue to rev up if i give it more throttle after it bogs. correct me if I am wrong, but if it were fuel I would think the RPMs would not continue to climb when more throttle is applied.

Thanks again for your help

Chris

JimN
06-29-2009, 10:47 PM
Jim thank for your help. one thing jumped out at me with your post. My boat idles at 650 to 700 RPMs. Am I looking at a vacuum leak probably? I took of the throttle body today and cleaned it. I am going to pick up a new gasket in the morning. It doesn't seem like a fuel problem to me because the motor will continue to rev up if i give it more throttle after it bogs. correct me if I am wrong, but if it were fuel I would think the RPMs would not continue to climb when more throttle is applied.

Thanks again for your help

Chris

Spray some carb cleaner around the base of the throttle body and if it raises the RPM, you'll know it's leaking somewhere. The MAP sensor hose can split and you may never see it. 700 RPM is high- make sure the IAC is closing completely, the MAP hose is intact and the PCV hose isn't loose on the valve or the throttle body base. If the PCV is really old, the spring may be weak enough to cause the RPM to increase at idle but it really shouldn't make it hard to go above 2800 RPM with throttle input.

In neutral, the RPM will usually go to about 2800, dip and then increase again as the throttle is moved through its range. If the throttle is increased slowly, this will be less noticeable but in gear and under load, you'll have a hard time going above 3K when the pump is weak or the fuel supply to it is reduced. I have seen this same symptom many times and if it wasn't the pump, it was almost always some restriction in the fuel supply. The steps I described in my last post should cure it if the pump is good. As I have also described, the recommended fuel pressure test is:

Key ON, engine OFF
At Idle
At 2000RPM, under load, on the water
At WOT, under load, on the water.

Obviously, if it can't make WOT, don't spend too much time trying to get that from it.

tcseward
07-03-2009, 10:07 PM
Thanks again Jim. I put on a new fuel pump today. I also took apart the fuel tank, and fuel feed line to check for restrictions. I took the throttle body off, cleaned it and put a new gasket under it. I replaced the vacuum lines and the PCV valve. I am still having the same problems. I checked the timing and it was 14 deg. BTC. I adjusted the timing to 10 deg. The problem still happens, but it does it at about 2500 RPMs now. I ran the DTCs again and it pulled a 21 and 33. I cleared the codes because I thought that it was showing them because I disconnected the sensors, and the same codes came up. The TP and MAP sensors are both new. What could be causing both codes? I did test the KS with the hammer trick, and it is working fine. It did not throw a code for the KS after I did the test. Any other suggestions? Could it be the ECM? Is there a way to test it?

Thanks,
Chris

JimN
07-03-2009, 10:54 PM
Thanks again Jim. I put on a new fuel pump today. I also took apart the fuel tank, and fuel feed line to check for restrictions. I took the throttle body off, cleaned it and put a new gasket under it. I replaced the vacuum lines and the PCV valve. I am still having the same problems. I checked the timing and it was 14 deg. BTC. I adjusted the timing to 10 deg. The problem still happens, but it does it at about 2500 RPMs now. I ran the DTCs again and it pulled a 21 and 33. I cleared the codes because I thought that it was showing them because I disconnected the sensors, and the same codes came up. The TP and MAP sensors are both new. What could be causing both codes? I did test the KS with the hammer trick, and it is working fine. It did not throw a code for the KS after I did the test. Any other suggestions? Could it be the ECM? Is there a way to test it?

Thanks,
Chris

Clearing codes may take more than one attempt. If you used a Corvette TPS, that would explain a code 22 but not a 21. The fact that both codes indicate low voltage tells me that you probably have a bad sensor ground, since both of these share the same one.

ANY TIME you have voltage issues, which includes codes that indicate low on a sensor, look at all of the grounds. For that matter, on any boat that's more than about 5 years old, inspect, clean and tighten all grounds on a regular basis. Repeat after me- "The positive and ground circuits are the most important of all". If these are bad, nothing can work as designed since all of the sensors are voltage dependent, other than the knock sensor.

If you want a definitive test for your ECM, send it to Indmar.

tcseward
07-04-2009, 10:05 AM
Jim, thanks again. after cleared the codes, I checked to make sure they were gone before I ran it again. Would the codes pop back up after I cleared them and give me false readings? This might be a dumb question, but where are the grounds for the engine?

Thanks,
Chris

JimN
07-04-2009, 11:57 AM
Jim, thanks again. after cleared the codes, I checked to make sure they were gone before I ran it again. Would the codes pop back up after I cleared them and give me false readings? This might be a dumb question, but where are the grounds for the engine?

Thanks,
Chris

False readings would be due to a bad (shorted or open) wire, bad ground or bad terminal. The ECM is programmed to send up a flare if the voltage returned through the sensor is above or below a specific range and unless you got two bad replacements (extremely unlikely), I would look at every terminal.

If you disconnect the ECM, make sure to remove the battery cables first. Look at the ECM's pins for any corrosion. If you see any crusty stuff around them, it means water got in. The terminals aren't very likely to corrode unless the plastic housing was left open but it can happen. There's only one correct terminal for the ECM, so if you need to replace any and someone says "This oughta work", run away. These use Packard terminals only.

The ECM, fuel pump, boat plug, starter solenoid and sensors ground at the rear of the motor. You'll need to remove the gas shocks form the stainless ball on the floor and remove the motor cover for this (I removed that any time I had to do anything other than general maintenance because it's hard enough to see back there but working with it in the way was just not efficient). Once that's gone, you can see everything. You'll need to remove the formed plastic cover on the solenoid and breaker for this. Use a wire brush to make sure you have bare metal and use some grease to keep it from corroding again.

BTW- if you had a computer for diagnostics, look at the voltage- if it's lower than what the dash gauge shows, it's definitely a bad ground at the rear of the motor. You may find that most of the strands are not connected to the ring terminal, so you'll need to replace it. If you strip the insulation and see black or green, cut the wire back and splice a new section in by soldering and covering it with heat shrink tubing (preferably Heat N Seal tubing), then crimp and solder a new ring terminal on. Use wire of at least the same gauge as the original and use the same color. NAPA has everything you'd need for this. If you don't have a soldering iron, they have crimp terminals and connectors that have low temperature solder inside and a match or lighter will melt it.

tcseward
07-06-2009, 09:53 AM
Thanks again Jim. I unbolted the ground and cleaned it and all of the terminals with a wire brush, and the boat still has the same issue. I decided to take the boat to the lake over the weekend (the closest lake is an hour away, so I have been diagnosing it in my drive way). I put the boat in and let it warm up. I used it all day Saturday pulling skiers / wake boarders. The boat worked without a problem????? I used it all day sunday without a problem as well until I tried to pull up two skiers. It started bogging down again. I turned the boat off and then back on and it work without a problem as long as I didn't pull two skiers. Any thoughts? This has stumped me. It bogs down in neutral in the driveway and with a big load, but it is fine with no load or a moderate load on the water.

Thanks again,
Chris