Tractionless

camptappakeg69

I agree with Bup too, I had the injectors cleaned and checked about 20 hrs ago, when I still was hopefull that one of my VST rebuilds would work. It seemed to help and ran strong.
Remembering a badly corroded distrubutor also was causing alot of issues for me one season, good luck finding your gremlin!

zz28zz

Have you pulled the spark plugs? Sounds like you're running very rich at idle. (EDIT: Just noticed you have confirmed plugs indicate over-rich condition)

I've seen many cars come in on the hook with the same symptoms. Probably half of those had a leaking vac line to the MAP sensor. A low vac signal from the MAP will make the ECM think the eng is under a serious load and dramatically increases fuel inj pulse width.

Exactly how did you test the MAP sensor?

We would use an o-scope on the signal wire for the TPS and MAP sensors cause they can fail in a way that produces high freq elec noise most prevalent when sensor input was in transition. With the TPS sensors we would connect the scope and very very slowly manually move throttle while monitoring scope. With the MAP sensors, we would connect them to a hand held vac pump and slowly increase vac while watching scope. A handheld DMM won't show the noise, at least when set to DC. You might see something if set to AC but a scope is waay better. ECMs hate noise and it can make them do weird things.

The coolant temp sensor falsely reporting -50 degs can also make the eng run way too rich. Verify the coolant temp sensor body is grounded with your multimeter. If it was installed with teflon tape, that can prevent a good ground and make sensor report to ECM that eng is ~-50 degs F. If the sensor is in the thermostat housing and the wrong gasket (or no gasket, just RTV) was installed, the coolant temp sensor can also loose it's ground.

I would try to test these signals at the ECM plug if possible just to rule out the wiring. As with any computer, garbage in, garbage out.

Another problem I chased for a few days on my own vehicle was an intermittent issue that would send a MAF error. Replaced MAF, no help. Wiring looked good. Eventually found a pin inside the connector would push back into the shell with little effort but when connector was unplugged, it would drop back into place. Might wanna look for that also. Plan on an oil change soon too. It may be getting diluted with fuel. Good luck..

Tractionless

I switched MAPS from one engine to the other and found no change. I'll inspect the vac hose as well as the harness pins as I did have that issue with the TPS and replaced its harness side plug.

As far as the coolant temp sensor, it's new and came with pre-treated threads for sealing but I'll check the ground.

I'm also going to replace the VST fuel pump due to the fuel pressure being so low.

Tractionless

UPDATE *Thanks everyone for your patience on awaiting new info.

I replaced the VST fuel pump.
Result: The engine didn't want to idle dead cold on the hose (85* ambient), would start and immediately stall. This is the same behavior as the old VST pump BUT The fuel pressure was 24 vac. line on and 34 vac. line off. So much higher vac lineoff pressure then the old pump (values previously posted), not sure if the old pump was just running lower pressure due to being heat soaked as testing was done on the water. Upon removing the vac line from the FPR the new fuel pump idled fine cold. Once warmed up it would idle with the vac line on the FPR but idled better with the vac line off. I don't understand why so much fuel pressure is being pulled with the vac line off the FPR when the manual specs. "the fuel pressure regulator maintains a constant fuel pressure of 34-36 psi." As I stated in a recent post above the FPR is a brand new genuine Merc. unit and I verified the correct part number for my application (also listed in said post).

Checks suggested from members above:

MAP Vac Line- Doesn't exist as the map bolts to a boss on the plenum, no leaks at the gasket.
MAP Harness Pins Loose etc.- Hooked to scanner and wiggled pins around etc. There wasn't any change in MAP signal.
Coolant Temp. Sensor Body and Ground Wire, Check for Ground- Both check out fine.
Ground Check for Injectors- I tested the unplugged ECU harness ground wires and they are fine.
Check VST Vent Hose to Plenum for Fuel- Zero present while running on hose when engine was stalling.
Check Vacuum- I Tee'd into the FPR vac. line and have 17 HG at steady idle with vac line off of the FPR and end of line capped. When I put the end on the FPR it goes to 15 HG. Spec. is 15-21 at Idle.
Check Plugs- Ran out of time last night.
Check Compression- Not sure it's necessary with the above vacuum numbers being in spec. Am I correct?

Again as stated above, I'm lost as to why the vac line on is pulling so much fuel pressure and feel this is the root of my problem.

Here's a couple of scanner screenshots vac. line off of the FPR. Once the vac line goes on the FPR, the IAC starts cranking up but all else is the same.

https://uniim1.shutterfly.com/ng/ser...886998/enhance

https://uniim1.shutterfly.com/ng/ser...886998/enhance

Keith

AllDodge

iTrader: (1)

Vac line OFF, fuel pressure UP to spec and idle smooths out, vac line ON fuel pressure DOWN below spec idle is bad. This is understandable, whats not is why a new pump and reg is doing this

I have a VST that was removed from my motor during my repower. It was working fine when removed, but has been sitting on a shelf since October 2014. I'll send it to you if you want to try

Tractionless

I greatly appreciate your offer. I have another VST on the sister engine that seems to be working fine and can use it if need be. That engine runs fine with 30psi idle fuel pressure.

I'm re-re-reviewing the Mercruiser #16 manual and finding (finally) on a flow chart on pg. 5C-61 that the fuel pressure should drop 3-10 psi during idle with the vac line on. The 34-38 psi is with the vacuum line off I suppose but not called out in that manner in any of the previous references within the manual so I assumed 34-38 psi was normal operating pressure, wrong. It appears my 26-28 psi with vacuum line on is satisfactory so why it's stalling at idle cold, hot (at times) and surging under partial throttle doesn't seem to be an overall fuel pressure issue. Maybe there's injector(s) sticking open (intermittently possibly) fuel starving others at low fuel pressures and when the vac line is pulled the lean injectors get fed and allow the engine to idle (thinking out loud).

As BUP previously noted a leaking fuel injector can be causing the problems. I'll pull the plugs and see what I have as far as fouling and move forward from there.

Found Reference
3. When the engine is idling, high vacuum is applied to the fuel regulator diaphragm. This will offset the spring and result in a lower fuel pressure. This idle vacuum will vary somewhat depending on barometric pressure; however, the fuel pressure at idle should be less, indicating fuel pressure regulator control.

4. Pressure that leaks down is caused by one of the following:
• Fuel pressure regulator valve leaking. -New unit and no fuel in the vac. line.
• Injector(s) sticking open.
• Check vent line from VST to see if diaphragm is leaking. -Rebuilt and zero fuel coming from the vent line when running.

camptappakeg69

Just remembered another issue on my engine, more of an intermittent no start. I checked all the wires running into the ecm/relay metal box on the top of engine, a couple of them had rubbed through the insulation and we're shorting out on the metal box.

Tractionless

Ok all, I pulled the plugs tonight 24 hrs. after idling on hose and dying as well as pulling the vac. line from the regulator to raise fuel pressure and keep it running. Here are the pics. I didn't smell any fuel upon removing any, maybe a small amount from SB bank front when putting damn near up my nostril, zero on the others. While I can compare to pics online I've never used plug condition to tune nor diagnose so I'll save it for the pros. but I don't feel they're rich nor fuel fouled. 62 hours on the plugs and they were installed new July of 2016.

What'cha think?

https://uniim1.shutterfly.com/ng/ser...008386/enhance

https://uniim1.shutterfly.com/ng/ser...008670/enhance

zz28zz

Hard to read the plugs from a pic, but don't see anything scary. Still getting fault codes?