Engine starts to miss / rough after 5-10 minutes with gas odor after 15

JohnEGraham said:
I did do a compression test before I replaced my manifolds and Risers and it all checked out fine at 165lbs plus or minus 5lbs after 4 compression strokes.
I did this early in the year due to water in the cylinder, and none in the oil. The water was due to the exhaust shutter falling out of place which I replaced.
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Great! What did the plugs look like?
 
Compression is good , gas or electrical prob and you said you have spark so that leaves fuel
 
Scott215 said:
Compression is good , has or electrical prob and you said you have spark so that leaves fuel
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Yes, that’s the way I’m headed now… I filled the tank with very expensive premium fuel… Change the filter/water separator… I clean the throttlebody and change leaking gasket… Which is causing engine to race… change the IAC , and the TPS…
 
JohnEGraham said:
Yes, that’s the way I’m headed now… I filled the tank with very expensive premium fuel… Change the filter/water separator… I clean the throttlebody and change leaking gasket… Which is causing engine to race… change the IAC , and the TPS…
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This doesn’t work? The new injectors, checking ignition coil… I was thinking of doing a “leak down test”
 
Any unmetered air entering engine is going to affect how it runs
 
JohnEGraham said:
This doesn’t work? The new injectors, checking ignition coil… I was thinking of doing a “leak down test”
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If your compression numbers are solid.....I wouldn't waste my time with a leak down test. We do leak down tests to determine why a cylinder is low on compression.

Throttle body systems were a compromise of sorts between carb systems and modern day Electronic Fuel Injection systems. They are closer to a smart carb than they are to multi point fuel injection.

In your case I am asking myself why is it going full rich under load? How do I know it is going full rich .....well the black plugs are a good indicator that you are getting at least twice the fuel you need into those cylinders. The TBI is controlled by the ECM so something is either telling the ECM it needs more fuel or it is happening outside the ECM's control. The two suspects in that world normally are the injectors and the fuel pressure regulator.

Yes it can still be electrical or something else but I would be taking a hard look at that fuel pressure regulator next just to ensure you have the right fuel pressure. If you post your engine serial number, I can look the part up for you but I think it uses this one: # 807952A1 it is a $50 part.

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PlayDate said:
If your compression numbers are solid.....I wouldn't waste my time with a leak down test. We do leak down tests to determine why a cylinder is low on compression.

Throttle body systems were a compromise of sorts between carb systems and modern day Electronic Fuel Injection systems. They are closer to a smart carb than they are to multi point fuel injection.

In your case I am asking myself why is it going full rich under load? How do I know it is going full rich .....well the black plugs are a good indicator that you are getting at least twice the fuel you need into those cylinders. The TBI is controlled by the ECM so something is either telling the ECM it needs more fuel or it is happening outside the ECM's control. The two suspects in that world normally are the injectors and the fuel pressure regulator.

Yes it can still be electrical or something else but I would be taking a hard look at that fuel pressure regulator next just to ensure you have the right fuel pressure. If you post your engine serial number, I can look the part up for you but I think it uses this one: # 807952A1 it is a $50 part.

View attachment 152399
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Hey John - the regulator goes to full pressure under load (engine vacuum is low) by design. Can't be that.
All of his spark plugs are fouling under load but the engine seems to be fine starting and light load.
That seems to eliminate the injectors as the problem.
Compression test shows good.
If the FPR failed the engine would be extremely rich at start and idling as the injectors are seeing full pump pressure.
Does this engine have an advance in the distributor? I have seen also the wires break going to the pickup inside of the distributor and they open circuit when it advances - but then again he said it is a new distributor.

Was the distributor phased when it was installed? If not correctly in phase that also can cause high speed cross fire and symptoms like he is seeing.

But, I still say his ignition system is breaking down under load - in a bad way.
 
ttmott said:
Hey John - the regulator goes to full pressure under load (engine vacuum is low) by design. Can't be that.
All of his spark plugs are fouling under load but the engine seems to be fine starting and light load.
That seems to eliminate the injectors as the problem.
Compression test shows good.
If the FPR failed the engine would be extremely rich at start and idling as the injectors are seeing full pump pressure.
Does this engine have an advance in the distributor? I have seen also the wires break going to the pickup inside of the distributor and they open circuit when it advances - but then again he said it is a new distributor.

Was the distributor phased when it was installed? If not correctly in phase that also can cause high speed cross fire and symptoms like he is seeing.

But, I still say his ignition system is breaking down under load - in a bad way.
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I tend to agree but I am struggling with this one. If it is electric......it is affecting all the cylinders the same since all the plugs are black. So it keeps running but the secondary spark is weak enough the plugs don't fire all the time? That would point to the pickup/coil distributor cap problem.......but it would be happening all the time not just when it was under load.

I still would like to know the fuel pressure. And I would like to understand what the ECM thinks is going on.

There have been a lot of part changes which also complicate the picture.

Perhaps the OP can share when the last time this engine ran correctly and give us a little more history specifically around when it started to behave like this. For example was it running well before the water intrusion?
 
PlayDate said:
I tend to agree but I am struggling with this one. If it is electric......it is affecting all the cylinders the same since all the plugs are black. So it keeps running but the secondary spark is weak enough the plugs don't fire all the time? That would point to the pickup/coil distributor cap problem.......but it would be happening all the time not just when it was under load.

I still would like to know the fuel pressure. And I would like to understand what the ECM thinks is going on.

There have been a lot of part changes which also complicate the picture.

Perhaps the OP can share when the last time this engine ran correctly and give us a little more history specifically around when it started to behave like this. For example was it running well before the water intrusion?
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Yup, I agree. A weak ignition system (weak spark or inconsistent spark) will deteriorate as cylinder pressures increase (load) and spark frequency (RPM) increases. A coil (for example) that isn't saturated (has a defect) when called upon to discharge will be a problem.
 
I checked the spray pattern with the timing lite and they where perfect cone shape. I checked the Resistance of the old and the new ignition coil both ther about the same. In installed the old one with same results.
I ran the boat with the hatch open and heard a crackling sounds…
 
PlayDate said:
I tend to agree but I am struggling with this one. If it is electric......it is affecting all the cylinders the same since all the plugs are black. So it keeps running but the secondary spark is weak enough the plugs don't fire all the time? That would point to the pickup/coil distributor cap problem.......but it would be happening all the time not just when it was under load.

I still would like to know the fuel pressure. And I would like to understand what the ECM thinks is going on.

There have been a lot of part changes which also complicate the picture.

Perhaps the OP can share when the last time this engine ran correctly and give us a little more history specifically around when it started to behave like this. For example was it running well before the water intrusion?
Click to expand...
Never heard of “Was the distributor phased when it was installed? If not correctly in phase that also can cause high speed cross fire and symptoms like he is seeing”
Can you explain how this is done?
 
I've heard of it being off a tooth on cam gear, but never phasesd wrong
 
Phasing is to set the distributor's rotor and reluctor (trigger) to crankshaft position. This is most important in distributors that have timing advance features built in like vacuum and mechanical advance. The trigger is what indicates the ECM to fire a coil pulse. The rotor is what directs the high voltage spark current to the correct cylinder. Let's say that the base timing is 8 degrees before number one piston top dead center firing. The distributor must have both the trigger and rotor in the correct position to enable that spark precisely to occur at that number one cylinder at 8 degrees BTDC. If, for example, the rotor is between the cap's number 1 and 8 pin the timing light will show a correct 8 degrees BTDC but possibly due to the position on the cam gear and trigger not being correct the high voltage needs to arc all the way to that number 1 pin inside of the cap and will significantly diminish the energy needed at the spark plug.

One thing not brought up is the MAP sensor and if that should be the issue...
 
I kinda get what you are saying. But if your at 8 degrees initial timing then your at 8 degrees. That's what #1 is telling you. So unless something is not right in the distributor, you should be at 8. Set idle timing then set total timing. The phasing would be in the turning of the distributor to set timing unless it is a distributor less ignition with a reluctor wheel some where
 
Agree with checking fuel pressure. Phasing wasn't a thing with that ignition system OP is running. Was it a new distributor or used?
 
PlayDate said:
If your compression numbers are solid.....I wouldn't waste my time with a leak down test. We do leak down tests to determine why a cylinder is low on compression.

Throttle body systems were a compromise of sorts between carb systems and modern day Electronic Fuel Injection systems. They are closer to a smart carb than they are to multi point fuel injection.

In your case I am asking myself why is it going full rich under load? How do I know it is going full rich .....well the black plugs are a good indicator that you are getting at least twice the fuel you need into those cylinders. The TBI is controlled by the ECM so something is either telling the ECM it needs more fuel or it is happening outside the ECM's control. The two suspects in that world normally are the injectors and the fuel pressure regulator.

Yes it can still be electrical or something else but I would be taking a hard look at that fuel pressure regulator next just to ensure you have the right fuel pressure. If you post your engine serial number, I can look the part up for you but I think it uses this one: # 807952A1 it is a $50 part.

View attachment 152399
Click to expand...
Hi, The fuel regulator is not adjustable. It’s a big spring. Serial # 0L010035
I was trying to check my fuel pressure today with an adapter kit that I got from Auto Zone but the TBI fuel connector was the wrong one, and it only did was cross thread, my TBI fuel intake line… I was getting about about 30 pounds even with it leaking… I took the boat to a friend who is marine mechanic… There were no codes… But when he put his shunt device on my DCL the boat would not go into service mode… So we did the best we could at the prescribed 600 RPMs to get it to 8° though it was jumping around a little bit…
Attacking on 2 fronts checking the fuel delivery and the timing once again…
 
ttmott said:
Phasing is to set the distributor's rotor and reluctor (trigger) to crankshaft position. This is most important in distributors that have timing advance features built in like vacuum and mechanical advance. The trigger is what indicates the ECM to fire a coil pulse. The rotor is what directs the high voltage spark current to the correct cylinder. Let's say that the base timing is 8 degrees before number one piston top dead center firing. The distributor must have both the trigger and rotor in the correct position to enable that spark precisely to occur at that number one cylinder at 8 degrees BTDC. If, for example, the rotor is between the cap's number 1 and 8 pin the timing light will show a correct 8 degrees BTDC but possibly due to the position on the cam gear and trigger not being correct the high voltage needs to arc all the way to that number 1 pin inside of the cap and will significantly diminish the energy needed at the spark plug.

One thing not brought up is the MAP sensor and if that should be the issue...
Click to expand...
I have a new map sensor to install… Since I did the IAC in the TPS why not…
 
JohnEGraham said:
I have a new map sensor to install… Since I did the IAC in the TPS why not…
Click to expand...
Thank you for all the information on the phasing… Also as I said, in a previous post seems to be some issues with Merccruiser shunt device not working and doesn’t put the boat into service mode… there were no codes for any other issues… But being in 1998 ? I guess items are limited… I’m going to check the wiring to see if there’s any issues from those connectors “A” “B” wiring Apparently the A pin goes to ground and the B pin goes to J17 on the ECM
I am guessing, as in most things with this boat it always seems to be an electrical corrosion poor grounding that causes the trouble in the end…
 
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