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notaloser

Repowered 5.7L MPI bogs under load

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notaloser

Hi all,

Looking for some guidance in troubleshooting my engine problem. Details are below.

I bought a storm damaged 01 Malibu Wakesetter Escape in December and repowered this year. I bought a new base engine and refurbished the old intake manifold, throttle body, injectors, fuel rail, fuel pump, etc. Everything that was reused from the old engine was thoroughly cleaned and inspected/tested. I also had the CEFI 3 ECU tested with no issue.

The new built up engine is now back in the boat. It starts cleanly, idles nicely at 650 RPM, and runs without issue at higher/variable RPM with no load. 

When I take it out, it runs nicely at low RPM until I attempt to get up on a plane. It feels like the acceleration is hesistant. I’ll take it up to 2500-3000 RPM and it will become bogged/lose power. After this happens and I back off, the idle is poor/rough and often stalls upon switching back to neutral. To start again, I have to start with throttle in neutral. After a minute or so of stable, no load running at 1000-2000 RPM, I can throttle back to then engage the transmission and idle back to the pier, usually a rough idle.

If I allow the engine to rest for a bit, I can start the process all over again with a clean start.

Things I have tried so far: inspected fuel lines for obstructions, tested fuel and found no water in tank, replaced water separating fuel filter (was clean upon removal), replaced IAC valve, checked for CEFI 3 codes (no codes thrown), and performed a fuel pressure test while experiencing the issues (35 psi constant idling, a little fluctuation while attempting to get on a plane up to 42 psi). The fuel pressure was measured at the fuel rail on the side opposite the regulator. 

Anyone have suggestions on what next to consider?

Thanks,

Will

 

P.S. I’ve noticed my oil pressure gauge reads constant at 60 psi at idle and increases up to 80 psi at ~2000 RPM, regardless of load. I have not yet performed an oil pressure test with my analog gauge, but plan to do so shortly. Seem too high?

 

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oldjeep

Sounds like the timing is off

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notaloser

Forgot to mention - I also re-checked base timing to 10 deg BTDC using an inductive timing light. Not sure the accuracy versus a digital timing tool, though. I supposed it could still be off? I know Indmar engines are sensitive to timing issues. 

All new distributor cap and rotor, spark plugs, and spark plug wires. Advance is set by the EST distributor module (from old engine). I haven’t quantified/confirmed how much advance it provides, but I did make sure it was advancing (no load). 

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MadMan

Have you pulled the plugs to see what they look like?  You could throw a MAP or TPS sensor at it.  Oil pressure sounds fine.

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notaloser

I had the #1 plug pulled for checking TDC and it did not appear to have any wear or damage. 

I think my next tests will be to pull/inspect all plugs and also test TPS, MAP and ECT sensors and connections back to the computer. 

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notaloser

Hi all,

I just completed a voltage drop test for the TPS and MAP sensors.

The TPS worked very nicely, consistent voltage drop increase as throttle was opened.

The MAP didn’t seem to work as expected, but documentation differs online and I’d like a second opinion. 

Upon turning the ignition on without starting the engine, the signal was 4.9 V (which to me sets a baseline for barometric pressure?). Upon starting it dropped to 1.2-1.5 V, and then DECREASED to 0.9 V upon opening the throttle. I didn’t open up too much since I’m running with no load on the lift, but I would have expected the sensor to increase with opening the throttle. Does that make sense?

Thanks,

Will

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justgary

That might happen with no load since you barely have to crack the throttle to get high RPMs.  What I'm thinking is that you crack the throttle, the RPMs go up, and vacuum actually increases because the butterfly is restricting the flow.  Things change when you have a load on the engine.  If I had my boat out, I would go test it for you right now, but it is raining today....

How high did you take it no load?  Does it act up at 3500 RPM in neutral?

I think that engine gets its spark timing from the distributor module, not a crankshaft sensor.  If you have access to an oscilloscope, it might help to watch that output to see that it isn't jumping all over the place when the trouble starts.  Check under the distributor (inside) and make sure that the module is clean and has a good ground, and that some stray metal chips have not gotten into the hall effect sensor magnet or on the interrupter star.

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notaloser

I didn’t take it up to 3500, but did to around 2000 and observed the .3V drop. 

I can probably borrow an oscilloscope from work but will have to wait until next week to try. I don’t suspect any issue with the distributor internals since it was just rebuilt, but will check next opportunity. 

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notaloser

I’m out of time to troubleshoot today but couldn’t help myself. I quickly hooked everything back up and ran up to 3500 no load, same behavior staying between 0.9 and 1.3 V.

By 3500 rpm, even with no load, the throttle position is far enough forward that I believe the vacuum should be decreasing in the manifold and the map voltage drop should be increasing.

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justgary
On 8/18/2018 at 10:22 AM, notaloser said:

I’m out of time to troubleshoot today but couldn’t help myself. I quickly hooked everything back up and ran up to 3500 no load, same behavior staying between 0.9 and 1.3 V.

By 3500 rpm, even with no load, the throttle position is far enough forward that I believe the vacuum should be decreasing in the manifold and the map voltage drop should be increasing.

I had to get my boat out to work on the trailer, so I ran the engine to get you some numbers from the MAP sensor:

KOEO - 4.85v

Warm 650 idle - 1.75v

3050 RPM - 0.92v

I think the vacuum will get bigger unless you load the engine.  But your sensor matches mine, so that's probably not it. 

The air temperature sensor can cause these symptoms also....

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notaloser

Dang... was really hoping for a win there.

My engine doesn’t have an air temp sensor which was surprising since MEFI/CEFI3 supports it.

Will check the plugs and confirm gap size, distributor internals, etc. next. 

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BoatFlyRide

Did you lock the engine in base timing mode before adjusting the distributor?

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notaloser

Yes, engine was in service mode for setting base timing. 

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justgary
58 minutes ago, notaloser said:

Dang... was really hoping for a win there.

My engine doesn’t have an air temp sensor which was surprising since MEFI/CEFI3 supports it.

Will check the plugs and confirm gap size, distributor internals, etc. next. 

The engine has to know temperature to run correctly.  What about the engine water temperature sensor? 

It makes sense that it would run right cold and very poorly hot if the temp sensor is bad. 

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notaloser

It does have a water temp sensor that I’ll check again to confirm it is in range and watch it’s output as the engine warms up. 

My understanding was that water temp was only used by ECU to make small changes to fuel injection to accommodate cold vs. hot condition. That said, the problem I’m having has always occurred after the engine has warmed up and I get out past the no wake zone. 

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notaloser

Latest updates:

On the recommendation of a mechanic, I pulled the injectors to be cleaned and flow characterized. Upon doing some research about GM Multec I injectors (terrible) I decided to replace with Bosch Design III injectors (24# at 43.5 psi to match) modified to fit by Fuel Injector Connection.

After installing the new injectors, the power problem was significantly less severe, but the same sequence of events occurred (ok at idle, start to throttle up under load, good for a short period, then start to lose power and return to rough idle).

I pulled all plugs and discovered carbon fouling that I am hoping was due to rich condition with old injectors. Cleaned all plugs and reinstalled; checked all plug wire resistances, verified all plug wire resistances were ok, distributor contacts clean inside and out, pickup coil resistance in range, ignition coil continuity checked out. Also checked ECT voltage and verified Ok at ambient temps - need to check after warming up.

 

Next I will measure ignition coil resistances and then try another on water test to again verify fuel pressure while operating, as well as check ECT voltage after engine is warm.

 

Appreciate any feedback - this forum has been very helpful for tests and checks to perform and as a sounding board for vetting my goofy logic. 

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BoatFlyRide

Another dumb idea but since you’ve just about checked everything it’s worth a shot...

Is the cam profile and compression ratio the same on your new short block as it was on the original engine?

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Fred2

I had a similar problem, changed the coil, problem gone

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notaloser

Success! Thank you all!

I replaced the ignition coil, fuel pump, and pressure regulator, and between the 3 it has been resolved. Since I had the issue before burning up my fuel pump last week (dumb), I suspect the ignition coil was the issue - despite the coils falling into the correct resistance ranges.

Thanks!

 

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