2003 DF90 wont stay running

[Lowery99]

Newly rebuilt 2003 DF90
First some info, then the symptoms

• ~210 pounds on all 4 cylinders
• No exhaust rot
• Engine was bought disassembled, tiny crack between 3 and 4 so the block was replaced
• Can hear the high pressure pump running when key is switched on
• MAP sensor and port have been cleaned
• VST has been cleaned out and checked
• Fuel filter before the low speed pump is clear
• Low speed pump verified pumping
• All electrical on the engine is original except coils which were bought used

What is happening

• Starts, but runs rough and will not idle for more than a minute or so
• With additional throttle it starts, rpm runs up and down randomly, stalls after a few minutes
• Check engine light when running, 3-2 MAP code when off

First inclination is the high speed pump, replacing it and MAP sensor as well. Any other ideas?

[redlowrey]

Lift the warm up leaver and bring the rpm up and try and locate which cyls are missing.
Any electrical or mechanical problem with engines
that use a map sensor will affect signal voltage because it uses manifold Vacuum for information.

For instance if you have got the valve timing late the map signal voltage will be sitting near 4. Volts drowning the cyls in fuel which will make it run bad on all cyls.

So find out if it is missing on all cyls From flooding or one or two this will Give some direction to take next.

[Lowery99]

Seems to be either all lean or rich, not smelling fuel so guessing lean. If I can even get the rpm to hold, pulling the plug wire or injector wire on all 4 affect the engine equally.

[redlowrey]

Are you in Australia.

[Lowery99]

Also, seems that if I can get the rpm up for a bit, then get a stall... it will not restart with throttle for a few minutes, has to go back to idle to start. I do have the high pressure pump ans map sensor on the way. Easy enough to replace both.

[Lowery99]

Are you in Australia.

No, States, outside Atl Ga

[redlowrey]

Are you a mechanic, did you assemble The engine,only reason l ask, very important that the valve clearance is right.
Wouldn’t it be easier to check fuel pressure Than pulling the vst apart and checking the operation of the map rather than just replacing.

[Lowery99]

It is getting pressure, at least at first. 12v on plug and can hear it spin up, also can see pressure on it the bolt on top of the rail is loosened. No gauge to actually test ongoing pressure, and I have seen this style pump before prime but not able to maintain over time. $35 and I have had this engine torn down about 4 times, so pulling the SVT is on the easy side of things. Not a mechanic, but my father and I are working on this project and between us probably have 25-30 rebuilds, that is why we took this on. Still only in the engine for about half its value, so another $60 for the map and pump is worth a try. After that all I can think of is ECU.

Hate to see these issues, bought the engine as a leftover from original owner after buying a df70 was cheaper than rebuilding this df90 at a shop, and the only issue was supposed to be the tiny crack in 3-4.

[Lowery99]

Tested what I could today. MAP sensor get 5v. Signal is 4.1v when key is on. After starting it bounces from 2.1v to 2.4v. Even run up to about 2500 rpm it stays bouncing 2.1-2.4v and never deviates. Seems the sensor is bad. Also when the key is kicked on, hp fuel pump clicks, does that 4-5 times, then after that seems to want to prime. Guessing it is also in a failing state but not quite dead. Will report back this week after new map and pump are tried.

[redlowrey]

A good Engine with good manifold vacuum should have around 1volt at idle and less than 2 mid throttle sounds like you’re a tooth out in valve timing. Sounds like low vacuum high signal voltage.
If you connect up a vacuum gauge you will have about 10” inches of mercury.

[Lowery99]

A good Engine with good manifold vacuum should have around 1volt at idle and less than 2 mid throttle sounds like you’re a tooth out in valve timing. Sounds like low vacuum high signal voltage.
If you connect up a vacuum gauge you will have about 10” inches of mercury.

Tested timing just to make sure today, showing the proper 8 degrees at around 1000 rpm, it would be way out if it was off a tooth. Also think it would run steady but poor if a tooth out, it is all over the place and for a time rarely it runs proper. Dont have a vacuum tester so just going to wait a few days to get the new map sensor and see what happens. After that and the new high pressure pump, likely going to a shop to diagnose the ecu. Thanks for the ideas though, always willing to check what I can to get this thing running. Putting in the work to make a "forever" pontoon boat that wont need much for years. Entire electrical/electronic rework too.

[Lowery99]

Just wanted to report back. After a new map sensor and high pressure pump the engine got a bit better was still doing the same.... dying at idle, higher rpm would surge, sputter, surge or die altogether. Came down to electrical or fuel, mechanicals were all right. Started thinking about spark, knew the coils were firing right, but what about after that, what if plug was grounding.

So after about 20 hours of troubleshooting, $12 in new plugs solved it. Old plugs were firing, but it seems one must have been firing signal to ground.

Engine fires right up and runs up smooth. Still have a bit of an issue with idle, feels a bit weak at idle like the IAC is closing up all the way. Have to play around with the IAC some more.