454 mag mpi running rich and using a lot of fuel

[cableguy1979]

I've pulled my plugs (autolite 25) and they are all black. Timing is @ 8 degrees, standing behind the boat smells like raw fuel, it uses a gallon of gas within 20 minutes or less just at idle. What can cause this. Fuel pressure is at like 30 psi and no fuel leaking anywhere.

 

[tpenfield]

Timing @ 8 degrees BEFORE TDC ? in base timing mode? All spark plugs firing?

Might have to hook a computer up to the engine to see what is going on.

 

[Scott Danforth]

fuel pressure is low, possibly leaking injectors

spec on fuel pressure is 43 psi

 

[achris]

Going to need, at the very least, a year and what ECU (MEFI1, 2, 3 or PCM or 555). Better still, an engine serial number.

As suggested by TP, a diagnostics computer connected up will tell a lot of stories.

Chris........

 

[alldodge]

autolite 25

Agree need more info, and also need to change those plugs. They don't cross to MR43T and are not nickle plated so it might seize in the head due to moisture

 

[cableguy1979]

Wow now we are talking good info!!! Its a 1996 454 MAG MPI serial 0F764338.

I thought fuel pressure was 30 PSI for these engines? Thats what the fuel pump pumps up to before it shuts off....I can double check that.

It is set to 8 degrees BTDC in base timing mode...should it be after?

I had put in cheap spark plugs to get everything running and good but Im wondering if there could be a performance difference in using the correct plug vs the Autolite 25's.

Lastly I know I need to take it to someone with a scanner BUT everyone wants a minimum of $110 to $150 dollars just to hook it up. I believe I could change all the sensors for this just don't want to throw parts at it or spend that much for them to say its normal for these engines. Will it detect a leaky injector? Will running some MMO through it possibly help it? i talked to the guy that owned the boat last and he said it normal for the boat to run at 1000 RPM at idle. Whats weird is I can cut the engine off and then start it back up and it will idle back at 750 to 800 RPM. I do know another guy that if he has the right computer will do it for $75 which should be reasonable IF he has the right computer as he stated.

Lastly I thought about buying the LED and putting in the test port and checking for codes but this wont do the same thing as looking at the running diagnostics right? Might find the offending sensor but might not if its something minor only happening while the engine is running.

 

[cableguy1979]

The Merc manual states 34-38 PSI for MAG Gen V MPI unless I just misunderstood it.

 

[tpenfield]

8 degrees BTDC, so that is fine

Gen V engine, should have the MEFI1 conroller

My standard 7.4L of that era is rated for 32-36 psi fuel pressure on the rail.

Idle speed should be around 600 RPM.

You can only go so far with wrenches and screw drivers on these MPI engines, because you cannot 'see' what the computer is actually doing. So, for example, in this situation I would be looking at the "desired idle speed", the "injector pulse time", and the "timing advance/retard" times in order to get a better understanding of the rich mixture condition. None of those things you can see with a code reader. You must have the real-deal software.

The Rinda Diacom is like $500 (or 1 trip to the repair shop) . . . but I have seen less expensive systems from ODB Diagnostiecs for the MEFI 1-4 controllers. . . Software and cable for around $200. Not sure if those are as 'plug 'n play' as the Rinda.

 

[alldodge]

The Merc manual states 34-38 PSI for MAG Gen V MPI unless I just misunderstood it.

Agree, and it could be your gauge is not accurate, but if it drops quickly after the pump stops, then there is a leak. It can be caused by the injectors, fuel pump or regulator

Articfriends (Smitty) on OSO is the best there is in my opinion, but I have not seen a ECT sensor on a MEFI 1 ECM. Now if the MAP is defective it could be giving more fuel

 

[tpenfield]

I'm pretty sure my engines have the MEFI-1's they have the ECT . . . also have the IAT, TPS, MAP, IAC, but that is about it.

 

[alldodge]

It does have a ECT switch, but not one (3 wire sender) which sends the signal to the ECM. Looking at the wiring diagrams in manual 16 I'm not finding one. Mine was the same as your before repower to MEFI 3

 

[tpenfield]

It does have a ECT switch, but not one (3 wire sender) which sends the signal to the ECM. Looking at the wiring diagrams in manual 16 I'm not finding one. Mine was the same as your before repower to MEFI 3

Sorry for the side track . . . mine might the an MEFI-2 :noidea: as I have the 2 wire ECT . Delphi P/N on the MEFI is 16220371 .

 

[cableguy1979]

So if in understand correctly since my ect is two wire the ecm will not adjust fuel based on the reading instead only report it?

 

[alldodge]

It should be all good, but if cableguy1979 has issue we can get back on track, which I think we have not left. The 2 wire ECT is a switch, it just has an independent ground instead of using the case. And your MEFI is a 1, not to many of the 2 were used, Think it was VP but cannot state for fact without digging deeper. My memory is not what it use to be (CRS)

http://mefiburn.com/

 

[alldodge]

So if in understand correctly since my ect is two wire the ecm will not adjust fuel based on the reading instead only report it?

Its only a switch and makes contact once the coolant temp reaches the preset value (thinking around 200 or so)

 

[alldodge]

Its only a switch and makes contact once the coolant temp reaches the preset value (thinking around 200 or so)

OK, your right Ted it is a sender and not a switch
Doesn't have much resolution, my mistake

 

[tpenfield]

Your MEFI should adjust fuel based on ECT, MAP and IAT. However, until you can get some visible data off of it, it is a complete guessing game

 

[achris]

Wow now we are talking good info!!! Its a 1996 454 MAG MPI serial 0F764338.

I thought fuel pressure was 30 PSI for these engines? That's what the fuel pump pumps up to before it shuts off....I can double check that.

That pressure is a tad low for this engine. Should be 34-38 psi.

It is set to 8 degrees BTDC in base timing mode...should it be after?

No, BEFORE TDC is correct.

I had put in cheap spark plugs to get everything running and good but Im wondering if there could be a performance difference in using the correct plug vs the Autolite 25's.

no, let's get the RIGHT spark plugs in. Injected engines are VERY sensitive to combustion events. The wrong spark plugs can upset the ECM maps quite dramatically.

Lastly I know I need to take it to someone with a scanner BUT everyone wants a minimum of $110 to $150 dollars just to hook it up.

Yes, that's just a blatant rip-off. Takes 2 minutes to hook up the diagnostics cable and another 1 minute to read and print off the codes. Buy the software for yourself... It'll save you money, and time, in the long term.

I believe I could change all the sensors for this just don't want to throw parts at it or spend that much for them to say its normal for these engines.

Problem with this philosophy is that if the problem is not a sensor, you're back to the beginning, with less money in your pocket.... :facepalm: Never like 'shotgun' diagnostics myself....

Will it detect a leaky injector?

The software also has an 'injector balance test', so yes, it will detect a leaky injector...

Will running some MMO through it possibly help it?

Probably not....

I talked to the guy who owned the boat last and he said it normal for the boat to run at 1000 RPM at idle.

That's just plain wrong!

What's weird is I can cut the engine off and then start it back up and it will idle back at 750 to 800 RPM.

I'd look at the throttle cable adjustment...

I do know another guy that if he has the right computer will do it for $75 which should be reasonable IF he has the right computer as he stated.

Lastly I thought about buying the LED and putting in the test port and checking for codes but this wont do the same thing as looking at the running diagnostics right? Might find the offending sensor but might not if its something minor only happening while the engine is running.

Having owned the Rinda $700 (Australia) software and adapter cable for a few years now.... Best investment I have made in the boat... Worth every cent, and then some.... Easy to use, and can very quickly rule out what is working... pays for itself the second time you use it...

 

[achris]

So if in understand correctly since my ect is two wire the ecm will not adjust fuel based on the reading instead only report it?

ALL ECUs require an engine coolant temperature input for fuel mapping. It's one of the foundation stones of fuel management. Even the 2 wire (resistive) sensor is an input used by the mapping software. Later ECUs used a 3 wire (voltage divider) sensor, due to the greater accuracy, but it's still for the same reason. The ECU uses that data to control the richness of the fuel. Cold engines need richer fuel mixtures, or they stall.... Some will remember the old 'choke' system on carburettored car engines (now I'm showing my age :facepalm

Chris........

 

[achris]

Your MEFI should adjust fuel based on ECT, MAP and IAT. However, until you can get some visible data off of it, it is a complete guessing game

Indeedy....