7.4L MPI Won't Start
11-15-2015, 08:08 PM
#1
7.4L MPI Won't Start
Hi guys,
Need some help here. I have a 2000 Baja 302 with twin 7.4L MPI's. One of the engines (stbd) died at speed and wont start. I have fuel pressure and spark, but the engine just turns over and over and wont crank. It acts like it's not getting spark, but there is spark at the coil and at the plugs. There are no codes.
Prior to this, the same thing happened and I had the distributor repaired. It cranked and idled fine, but once I pushed it up to speed, the stbd engine died again. Suspicion from the mechanic at this point is the spark control module, but we cannot find it. We've looked all over the motor and cannot find this little module anywhere. The part number is 861535T.
You can see the part (#2) on this diagram (http://www.boats.net/parts/search/Me...NTS/parts.html), but we can't find an engine-layout diagram that actually shows where this thing is mounted. The diagram seems to indicate that it would be near the engine control and ECM modules, but we just don't see it.
If any of you know where it is and can tell me where to look, or send a picture, that would be great.
Some more history -- we've been chasing ghosts on this engine for a while now. The engine runs smooth, but fails to produce full power. At WOT, the engine would start to backfire internally -- best way I can describe it... like a popping sound inside the engine... no a mechanical clank/bang, but like a backfire internally. If I back off the throttle to less than 3800 rpm, it runs like a champ. Conclusion was that it's something electrical. We found a bad injector, replaced almost every component in the distributor, replaced the coil, ignition module, all plugs and the control module (blue box). We swapped the ECM from the port motor to the stbd side to see if the problem moved with it and to rule in/out an ECM problem, but swapping the ECM made no difference.
Throughout the hunt, as described above, we found a few other issues and repaired them. Now, we have complete failure to start. When we took apart the distributor, we found that the coil (P# 811639T) was cooked... like it had been melted. So, we replaced it and the engine cranked up and then failed again as described earlier. We are not convinced we haven't cooked the coil again and will take the distributor apart this week, but if we have, then the question is, what's cooking it? Mechanic's thought is the spark control module. We're running out of options as we've replaced (or swapped between motors) almost every electrical component we can find.
Any troubleshooting ideas would also be appreciated.
Thanks to you all in advance,
-Michael
Need some help here. I have a 2000 Baja 302 with twin 7.4L MPI's. One of the engines (stbd) died at speed and wont start. I have fuel pressure and spark, but the engine just turns over and over and wont crank. It acts like it's not getting spark, but there is spark at the coil and at the plugs. There are no codes.
Prior to this, the same thing happened and I had the distributor repaired. It cranked and idled fine, but once I pushed it up to speed, the stbd engine died again. Suspicion from the mechanic at this point is the spark control module, but we cannot find it. We've looked all over the motor and cannot find this little module anywhere. The part number is 861535T.
You can see the part (#2) on this diagram (http://www.boats.net/parts/search/Me...NTS/parts.html), but we can't find an engine-layout diagram that actually shows where this thing is mounted. The diagram seems to indicate that it would be near the engine control and ECM modules, but we just don't see it.
If any of you know where it is and can tell me where to look, or send a picture, that would be great.
Some more history -- we've been chasing ghosts on this engine for a while now. The engine runs smooth, but fails to produce full power. At WOT, the engine would start to backfire internally -- best way I can describe it... like a popping sound inside the engine... no a mechanical clank/bang, but like a backfire internally. If I back off the throttle to less than 3800 rpm, it runs like a champ. Conclusion was that it's something electrical. We found a bad injector, replaced almost every component in the distributor, replaced the coil, ignition module, all plugs and the control module (blue box). We swapped the ECM from the port motor to the stbd side to see if the problem moved with it and to rule in/out an ECM problem, but swapping the ECM made no difference.
Throughout the hunt, as described above, we found a few other issues and repaired them. Now, we have complete failure to start. When we took apart the distributor, we found that the coil (P# 811639T) was cooked... like it had been melted. So, we replaced it and the engine cranked up and then failed again as described earlier. We are not convinced we haven't cooked the coil again and will take the distributor apart this week, but if we have, then the question is, what's cooking it? Mechanic's thought is the spark control module. We're running out of options as we've replaced (or swapped between motors) almost every electrical component we can find.
Any troubleshooting ideas would also be appreciated.
Thanks to you all in advance,
-Michael
11-15-2015, 09:01 PM
#2
Hi guys,
I'm not sure what I'm looking at here. Some diagrams indicate this engine is an L29, others don't. The L29 shows a spark control module, but others seem to have it omitted. The engine serial number is 0L633801. The engine cover has "7.4litre MPI", and the placard shows "MCM 7.4 Litre MPI", but parts lookups online refer to it in various ways... some Gen IV, others L29. As subtle as these indications are, they apparently make a big difference electronically.
The service manual has several of the MCM's listed... MEFI-2 (also L29) and MEFI-3. The L29 shows a spark control module. The MEFI-3 does not.
Given that we can't find the spark control module, it makes me think this may be a MEFI-3, but how can I know for sure?
I'm not sure what I'm looking at here. Some diagrams indicate this engine is an L29, others don't. The L29 shows a spark control module, but others seem to have it omitted. The engine serial number is 0L633801. The engine cover has "7.4litre MPI", and the placard shows "MCM 7.4 Litre MPI", but parts lookups online refer to it in various ways... some Gen IV, others L29. As subtle as these indications are, they apparently make a big difference electronically.
The service manual has several of the MCM's listed... MEFI-2 (also L29) and MEFI-3. The L29 shows a spark control module. The MEFI-3 does not.
Given that we can't find the spark control module, it makes me think this may be a MEFI-3, but how can I know for sure?
11-16-2015, 01:14 AM
#3
Charter Member # 55
Charter Member
If your mechanic can't tell exactly what engine you have, how do you expect him to have the knowledge to fix it????
The ECM will say right on it exactly what it is. Also, any Merc certified mechanic can run the engine serial number to find out what it is.
The ECM will say right on it exactly what it is. Also, any Merc certified mechanic can run the engine serial number to find out what it is.
11-16-2015, 06:24 AM
#4
Suck, squish, bang, blow.
You have spark.
You have fuel pressure (did you verify proper pressure with gauge?)
Do you have injector pulse?
Do you have compression?
Have you done a fuel quality test?
Find out the answers to these questions before you jump into individual component tests.
Give a quick shot of ether into the intake plenum. Put the spark arrester back on, and see if the sputters or briefly starts and dies. If it does stop looking at spark for now. If it does not then you should investigate spark at the plug again and make sure it is strong.
Check at a fuel injector with the key on for 12 volts on one of the wires. Typically this will be a common wire color with all the injectors. If you have 12 volts key on, next step is to see if you have pulse on the ECM triggered ground wire in the injector plug. I use a noid light for this but it can be accomplished with a test light. Hook the alligator clip to +12 volts and probe the opposite wire with the pointy end while somebody cranks the motor. You should see a faint, rythmic flickering. If so the injectors are being triggered.
You have spark.
You have fuel pressure (did you verify proper pressure with gauge?)
Do you have injector pulse?
Do you have compression?
Have you done a fuel quality test?
Find out the answers to these questions before you jump into individual component tests.
Give a quick shot of ether into the intake plenum. Put the spark arrester back on, and see if the sputters or briefly starts and dies. If it does stop looking at spark for now. If it does not then you should investigate spark at the plug again and make sure it is strong.
Check at a fuel injector with the key on for 12 volts on one of the wires. Typically this will be a common wire color with all the injectors. If you have 12 volts key on, next step is to see if you have pulse on the ECM triggered ground wire in the injector plug. I use a noid light for this but it can be accomplished with a test light. Hook the alligator clip to +12 volts and probe the opposite wire with the pointy end while somebody cranks the motor. You should see a faint, rythmic flickering. If so the injectors are being triggered.
11-16-2015, 11:50 AM
#5
Banned
iTrader: (9)
Engine serial # is ?
Is your engines and drives stock OEM apps from mercruiser ?
Just because you have fuel pressure does not mean it is flowing properly thru the injectors or even at all
Your mechanic does not know the difference between MEFI 1 or MEFI 2 or MEFI 3
OEM Stock 2000 years models used MEFI 3 but who knows what you have here especially without eyes on it.
How advance is your mechanic with marine fuel injection ?
Mefi 1 mounting holes center hole to hole length wise is 6.5 inches they have 4 mounting holes, MEFI 2 is 4.75 inches length center to center mounting holes and has 4 mounting holes and MEFI 3 a smaller ECM and more square looking. It has 3 mounting holes.
Important - injector banks for L29 is 1,3,5,7 / 2,4,6,8. Injector banks for for all other MPI models are 1,4,6,7 / 2,3,5,8. MEFI
Have no idea what ignition you have but if EST coil has melted check for a grounded tach wire in the engine harness and or boat harness and or a bad TACH, Also check for any add on and or accessory wires connected to the shop tach only bullet connector on the engine. This can be a common from stupid people who use that connection.
next does the engine scan at anytime show general Diagnostic trouble code reading ??? if so I know what your problem is.
Does your engine at the starter have a 55 amp or a 90 amp block fuse mounted ?
Spray some carb cleaner down the throttle body not too much - so does the engine start ?
Do you guys know what clear flood mode is ? Your tech should ? Do that procedure while trying to start the engine - did engine start ?
If your tech does not know anything here from my post, I would find another tech who is trained on advanced MPI Mercruiser systems. FYI - I am by far if your tech says to the account of "I can careless about internet mechanics".
Where are located ?
Is your engines and drives stock OEM apps from mercruiser ?
Just because you have fuel pressure does not mean it is flowing properly thru the injectors or even at all
Your mechanic does not know the difference between MEFI 1 or MEFI 2 or MEFI 3
OEM Stock 2000 years models used MEFI 3 but who knows what you have here especially without eyes on it.
How advance is your mechanic with marine fuel injection ?
Mefi 1 mounting holes center hole to hole length wise is 6.5 inches they have 4 mounting holes, MEFI 2 is 4.75 inches length center to center mounting holes and has 4 mounting holes and MEFI 3 a smaller ECM and more square looking. It has 3 mounting holes.
Important - injector banks for L29 is 1,3,5,7 / 2,4,6,8. Injector banks for for all other MPI models are 1,4,6,7 / 2,3,5,8. MEFI
Have no idea what ignition you have but if EST coil has melted check for a grounded tach wire in the engine harness and or boat harness and or a bad TACH, Also check for any add on and or accessory wires connected to the shop tach only bullet connector on the engine. This can be a common from stupid people who use that connection.
next does the engine scan at anytime show general Diagnostic trouble code reading ??? if so I know what your problem is.
Does your engine at the starter have a 55 amp or a 90 amp block fuse mounted ?
Spray some carb cleaner down the throttle body not too much - so does the engine start ?
Do you guys know what clear flood mode is ? Your tech should ? Do that procedure while trying to start the engine - did engine start ?
If your tech does not know anything here from my post, I would find another tech who is trained on advanced MPI Mercruiser systems. FYI - I am by far if your tech says to the account of "I can careless about internet mechanics".
Where are located ?
Last edited by BUP; 11-16-2015 at 01:52 PM.
11-19-2015, 12:53 AM
#7
Hi guys,
Thanks for all the replies. The engine is a MEFI-3 so it looks like it does not have the spark control module. At least that's one less electrical component to worry about.
BUP - I'm in the middle of NC... kind of out in the country. I trust my mechanic... he freely admits that he's not overly familiar with these big MPI engines... there just aren't many of these engines around here. The next closest area that *might* have a mechanic more familiar is almost 2 hours away. I have two boats, both Baja's, and he's the only one I let work on them. There are some things he's had to learn on this big one, but he takes it as a personal challenge and doesn't charge me for the time he spends learning. I would rather have a mechanic tell me he doesn't know something than lie about it. He's not above asking online for ideas that he may not have thought of.
The boat never throws any codes... no numbers, letters or ??? --- it just says "No Codes to Display". There haven't been any stored codes either. I'm not sure of the starter fuse amperage, but we checked all the fuses and they are all ok.
We're as positive as we can be that it's not fuel delivery, pressure or injectors. Those were the first systems we checked and addressed anything we thought might contribute at all. I suppose we cant rule anything out 100% just yet, but why would it run fine, die, run again fine once the distributor coil was replaced, and then die again if it were injectors or fuel-related? I could see it if maybe when I punched-it the fuel pumps (it has the anti-vaporlock aux pump kit installed) couldn't feed it and it would sputter-out, but that's not what happened. It died instantly and wouldn't restart.... when it had been started/stopped 20+ times just prior to that run.
I'm very interested to see if we cooked that coil again. If we did, I think that might help focus our search to a specific electrical area. We have to wait for better weather before we can dig that deep into it again.
Once the weather clears we'll take a look at some of the items you guys have suggested and see what we can find.
Thanks again to you all for your help.
Thanks for all the replies. The engine is a MEFI-3 so it looks like it does not have the spark control module. At least that's one less electrical component to worry about.
BUP - I'm in the middle of NC... kind of out in the country. I trust my mechanic... he freely admits that he's not overly familiar with these big MPI engines... there just aren't many of these engines around here. The next closest area that *might* have a mechanic more familiar is almost 2 hours away. I have two boats, both Baja's, and he's the only one I let work on them. There are some things he's had to learn on this big one, but he takes it as a personal challenge and doesn't charge me for the time he spends learning. I would rather have a mechanic tell me he doesn't know something than lie about it. He's not above asking online for ideas that he may not have thought of.
The boat never throws any codes... no numbers, letters or ??? --- it just says "No Codes to Display". There haven't been any stored codes either. I'm not sure of the starter fuse amperage, but we checked all the fuses and they are all ok.
We're as positive as we can be that it's not fuel delivery, pressure or injectors. Those were the first systems we checked and addressed anything we thought might contribute at all. I suppose we cant rule anything out 100% just yet, but why would it run fine, die, run again fine once the distributor coil was replaced, and then die again if it were injectors or fuel-related? I could see it if maybe when I punched-it the fuel pumps (it has the anti-vaporlock aux pump kit installed) couldn't feed it and it would sputter-out, but that's not what happened. It died instantly and wouldn't restart.... when it had been started/stopped 20+ times just prior to that run.
I'm very interested to see if we cooked that coil again. If we did, I think that might help focus our search to a specific electrical area. We have to wait for better weather before we can dig that deep into it again.
Once the weather clears we'll take a look at some of the items you guys have suggested and see what we can find.
Thanks again to you all for your help.
11-19-2015, 06:17 AM
#8
Did you ever try the quick shot of ether or carb cleaner trick? That will tell you quickly if you have spark or not. If I was diagnosing this motor I would do this quick and easy test rather than trying to diagnose based on the symptoms of the shutdown.
11-19-2015, 09:56 AM
#9
Platinum Member
Platinum Member
If the popping sound you describe is the sound I'm thinking of, you might have a cracked head or blown head gasket. If the cyliders can't build pressure, motor won't start. Did you compression and leak down test. Just a thought.
11-19-2015, 10:48 AM
#10
Banned
iTrader: (9)
Clear flood mode procedure while starting try this and if still no start then try carb cleaner down the intake
Inline sealed spark checkers on all 8 while cranking the engine over and or starting it will tell you alot about that side of it
Glad you have a tech that is up front about all of it. If he is good at what he already knows and knows the basics step by step then he should be able to find the problem with your app. If he is a outboard tech ONLY I would question mark about all of this. just saying.
Inline sealed spark checkers on all 8 while cranking the engine over and or starting it will tell you alot about that side of it
Glad you have a tech that is up front about all of it. If he is good at what he already knows and knows the basics step by step then he should be able to find the problem with your app. If he is a outboard tech ONLY I would question mark about all of this. just saying.
