350 Mag Mpi hard to start when warm or hot

[alldodge]

We're still guessing, need to scan the motor and see what is happening

 

[nigb]

We're still guessing, need to scan the motor and see what is happening

Update 3:
I can't get a diagnostic done for a couple of weeks. In the meantime I checked the map sensor signal voltage at idle & it was 2.6v when the ecm 555 manual specifies 1 - 2v. I put a new non oem map sensor on & that also reads 2.6v & when I open throttle it drops to 1.6v which is strange as manual says it should increase. Sensor ref volts good at 5v. Is the 2.6v reading telling me I have low manifold pressure at idle?

 

[silver_power]

Update 3:
I can't get a diagnostic done for a couple of weeks. In the meantime I checked the map sensor signal voltage at idle & it was 2.6v when the ecm 555 manual specifies 1 - 2v. I put a new non oem map sensor on & that also reads 2.6v & when I open throttle it drops to 1.6v which is strange as manual says it should increase. Sensor ref volts good at 5v. Is the 2.6v reading telling me I have low manifold pressure at idle?

I had the exactly same problem to my 350Mag mpi (MY2009-1A348183). When cold was starting immediately but when warm (stopped more that 10mins) it wanted to give some throttle to start. I gave my injectors for professional inspection - cleaning and after that no more issues. I had made all the checks you have already done.......
I hope this will be your solution.

 

[dubs283]

With reading out of spec at the map sensor and a new map sensor installed I would be inspecting other sensors/components that share the same 5v reference as the map sensor

Good idea to verify all grounds on said circuit are okay along with no shorts to ground on any voltage/ref and signal wires

 

[alldodge]

Check resistance of ECT cold and hot

I put a new non oem map sensor on & that also reads 2.6v & when I open throttle it drops to 1.6v which is strange as manual says it should increase. Sensor ref volts good at 5v. Is the 2.6v reading telling me I have low manifold pressure at idle?

Changing more parts can induce more issues
As the throttle increases further does the voltage start to increase then, or still lower? Your sensor is a MAP and TMAP, so it measures pressure and Temp. As Temp rises ohms lower

 

[nigb]

I had the exactly same problem to my 350Mag mpi (MY2009-1A348183). When cold was starting immediately but when warm (stopped more that 10mins) it wanted to give some throttle to start. I gave my injectors for professional inspection - cleaning and after that no more issues. I had made all the checks you have already done.......
I hope this will be your solution.

Thanks for reply. I did consider injectors at 1st but as the fuel rail was holding pressure I discounted that. Might rethink that now.

 

[silver_power]

Thanks for reply. I did consider injectors at 1st but as the fuel rail was holding pressure I discounted that. Might rethink that now.this is the rule.....if

Thanks for reply. I did consider injectors at 1st but as the fuel rail was holding pressure I discounted that. Might rethink that now.

You are correct and that is why the injector inspection was the last thing i did...just because the pressure did not dropped too much and was holding about 30psi after about 10mins if i remember correct.
But, this solved my problem. Maybe the spray pattern was not good and in warm conditions was not the ideal for starting the engine.
I remember that a some times the engine could start when warm but with very low revs, approx 250 and needed some throttle to go to 550rpm. But most of the times, the engine could not start without throttle.
After injector service, all good, and engine was starting cold or hot at the rpms that should have according sensor parameters.

 

[nigb]

Check resistance of ECT cold and hot
View attachment 381713

Changing more parts can induce more issues
As the throttle increases further does the voltage start to increase then, or still lower? Your sensor is a MAP and TMAP, so it measures pressure and Temp. As Temp rises ohms lower

Thanks for reply. I will double check ect values in morning (night time here in Oz). As I increased the revs it seemed to progress to around 1.6v & stay there but I will check again.

 

[nigb]

With reading out of spec at the map sensor and a new map sensor installed I would be inspecting other sensors/components that share the same 5v reference as the map sensor

Good idea to verify all grounds on said circuit are okay along with no shorts to ground on any voltage/ref and signal wires

Thanks for reply. I had ground connection on my multimeter attached to the battery when i checked sensor 5v when it should probably have been on engine ground. I will recheck tomorrow.

 

[nigb]

Update 4: Boat booked in for a diagnostic test next Tuesday. I have checked grounds to other sensors all ok. However I did attach a vacuum gauge to the Inlet manifold & it is reading 12 Hg when it should be around 17-18 Hg so the map sensor is reading correctly. I will get them to compression test too though my mechanic says the boat is performing too well to have mechanical issues & he has never seen an mpi engine blow a head gasket apart from one with heavy internal corrosion. I could do compression test myself but the 2 front plugs on either side look a bit hard to get to!
I have put a new ect sensor in too. My mechanic agrees I have tried everything & to get diagnostic test done.

 

[FunInDuhSun]

I had the same engine (and year) on one of my boats. Had a similar issue and -after wasting most of a summer- they figured out the coil was overheating and causing a weak signal. Swapped in another coil and all was good. Might be worth a try!

 

[nigb]

I had the same engine (and year) on one of my boats. Had a similar issue and -after wasting most of a summer- they figured out the coil was overheating and causing a weak signal. Swapped in another coil and all was good. Might be worth a try!

Interesting I hadn't considered coil. I hope it is something as simple as that. Thanks for reply

 

[Scott06]

Interesting I hadn't considered coil. I hope it is something as simple as that. Thanks for reply

In the manual there will be ohm specs for coil primary and secondary sides easy to test

 

[nigb]

In the manual there will be ohm specs for coil primary and secondary sides easy to test

Thanks just found it in manual will try that before diagnostic test.

 

[nigb]

Update 5: diagnostic revealed misfire on cylinder 8. Plug burnt electrode & black. Replaced spark plug now starts when hot. Tech said still a misfire which I couldn't hear until he pointed it out. Compression test revealed only 5 psi on that cylinder so I either have hole in piston, damaged rings or exhaust valve problem. Won't know until tomorrow when we investigate further. I have an inspection camera I can put in bore. The low vacuum reading I had pointed to valve timing which obviously it couldn't be but when I saw it I thought it was a mechanical issue. Boat is going better than it ever has with no noises or excessive oil consumption or smoke!

 

[nigb]

Camera down plug hole bit tricky to decipher at 1st but in the bottom 1/3 of pic is the original cross hatching of the cylinder & valve open on right. In middle of pic you can see outer circumference of piston - no visible damage. The top half of pic I believe is a piston surface that has been pressure washed with fuel by the injector after spark plug died. Unburnt fuel out of exhaust would explain passengers in boat complaining of fuel smell. With engine running there is no pressure pulses coming out of oil filler which one would expect with a holed piston. I suspect (hope!) it is a stuck valve.

 

[nigb]

Put my leak down tester on today & I have air coming out of the intake plenum so looks like a fault with the Inlet valve. With my camera I can see valve opening as I rotate engine but it doesn't seem to be seating properly. I can actually see it standing proud at tdc. Can't think what would be causing this. Tomorrow I will take exhausts & risers off so can get to rocker cover. Stay tuned!

 

[nigb]

Good news but I am a bit confused here might need some help. It was exhaust valve that was stuck open. Exhaust valve on no 7 was not stuck open it was because rocker arm was tight. As soon as I loosened rocker arm off it closed. Did compression test still zero. Noticed no 7 Inlet was slightly tight. Backed it off 1/2 a turn & get 130 psi on cold engine. I notice on no 1 cylinder at tdc I can lift the rocker arm off the valve until spring in lifter seats. I can't feel this on no 7. Do I assume there is a problem with the hydraulic lifters I.e. oil not draining out? I presume I have to remove Inlet manifold to check those unless there is a trick to free them? Also explains why I had air coming out of plenum when doing leak down test.

 

[alldodge]

Should not feel any slop on rockers. Valves should be adjusted to 1 turn past zero lash. The valves shouldn't have tightened so maybe prior owner did some incorrect adjusting

Ones that have slop look close at rocker nut to see it stud looks to have more or less threads extending out from nut. If just a couple threads then no issue, but if more , this could be a concern

 

[nigb]

Should not feel any slop on rockers. Valves should be adjusted to 1 turn past zero lash. The valves shouldn't have tightened so maybe prior owner did some incorrect adjusting

Ones that have slop look close at rocker nut to see it stud looks to have more or less threads extending out from nut. If just a couple threads then no issue, but if more , this could be a concern

Thanks for reply. I screw rocker nut down until no lash or play. But when I tighten 360 degrees as per manual it opens the valve. Is that correct?