Absolutely frustrated with this Mercruiser engine

For those suggesting that I scope the intake or try to unplug the fuel injectors while its running that's not really feasible. This engine has a plenum that houses all the sensors and the throttle body. In order to gain access to the injectors in any way the plenum has to be removed. I can test fuel pressure at the rail which holds at 37 psi throughout the entire throttle range. But testing items under the plenum while the engine is running is just really really hard to do. I don't have any photos of the plugs but they are all new and from the few hours they have run on the engine they all are slightly light brown and show no indications of any damage, oil or carbon fouling.

Capture.JPG
 
A little injector harness testing for dummies (like me)
If you can get to the wire keeper on the injector, you should be able to disconnect the injector plug. Heed the previous statement about how easy it is to break the connector on the injector. I chased intermittent connections for a long time once upon an engine.
 
Hoplite808 said:
.... I can test fuel pressure at the rail which holds at 37 psi throughout the entire throttle range. ....
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I don't know this implementation very well, so excuse me if this is a more 'generic' question....

Is the fuel pressure (regulator) supposed to be referenced to manifold pressure? Should the fuel pressure go down when the load (absolute manifold pressure) goes down?
 
km1125 said:
I don't know this implementation very well, so excuse me if this is a more 'generic' question....

Is the fuel pressure (regulator) supposed to be referenced to manifold pressure? Should the fuel pressure go down when the load (absolute manifold pressure) goes down?
Click to expand...
The fuel pressure regulator is controlled by manifold pressure. When manifold pressure goes up (more engine load) fuel pressure goes UP.
 
Hoplite808 said:
For those suggesting that I scope the intake or try to unplug the fuel injectors while its running that's not really feasible. This engine has a plenum that houses all the sensors and the throttle body. In order to gain access to the injectors in any way the plenum has to be removed. I can test fuel pressure at the rail which holds at 37 psi throughout the entire throttle range. But testing items under the plenum while the engine is running is just really really hard to do. I don't have any photos of the plugs but they are all new and from the few hours they have run on the engine they all are slightly light brown and show no indications of any damage, oil or carbon fouling.

View attachment 144949
Click to expand...


I agree it would be hard to do on the engine. However, it is possible to do it at the ECM.

Effectively you would be looking at pins J2-21, J2-5 which are the injector drivers and J2-15, J2-20 which are the injector grounds. The injectors (J2-21, J2-5) receive battery power from the ECM fuse. The ECM completes the circuit to ground triggering the injector. It does this on pins J2-15, J2-20. Page 46 of the manual I listed earlier.

Since this is "bank fired" .....there are only two banks of injectors. Using an inductive noid light, scope or even a DVM on these two pins will tell you if the bank is firing. You don't need to see every injector just determine if both banks are firing at full throttle.

Again, I would try putting it in to Service mode first since that is easy and may work.

We need to bottom out why you are not getting fuel. In my view, monitoring the two injector circuits and giving Service mode a try are the next steps.
 
ttmott said:
The fuel pressure regulator is controlled by manifold pressure. When manifold pressure goes up (more engine load) fuel pressure goes UP.
Click to expand...
Ok, then why would he be measuring "37 psi throughout the entire throttle range" ?
 
km1125 said:
Ok, then why would he be measuring "37 psi throughout the entire throttle range" ?
Click to expand...
Yea - not sure. I don't know what the range is for his engine but typically at low manifold pressure (engine idle conditions) the fuel rail pressure is typically 32 PSIG and increases linearly to 43 PSIG at atmo pressure.
 
ttmott said:
Yea - not sure. I don't know what the range is for his engine but typically at low manifold pressure (engine idle conditions) the fuel rail pressure is typically 32 PSIG and increases linearly to 43 PSIG at atmo pressure.
Click to expand...


Also .....his "throttle range" at present is 600-2000 rpm under load. So I seriously doubt that he would see any major difference in fuel pressure over that range especially since the injectors don't appear to be calling for more fuel. If fuel pressure was dropping over that range......I would have a different conclusion.
 
PlayDate said:
Also .....his "throttle range" at present is 600-2000 rpm under load. So I seriously doubt that he would see any major difference in fuel pressure over that range especially since the injectors don't appear to be calling for more fuel. If fuel pressure was dropping over that range......I would have a different conclusion.
Click to expand...
But, the data shows his MAP at atmo. So even at 2000 rpm his fuel pressure should be max; whatever that is. Regardless, the fuel pressure as long as it is over 30 psig should support any RPM condition. The ECM will compensate the injector pulse rate to achieve a throttle position / RPM.
 
PlayDate said:
Tom,
What are you putting this monster into?

index.php
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This is a motor I had Roush build for my 1970 Plymouth Cuda. It is a 545 CI twin turbo setup with a Holley Dominator EFI engine management system. We are working on the chassis right now. I'm setting up the car for track days.
IMG_7329.jpg
IMG_1267 rotated.jpg
 
These two posts don't make any sense to me:

PlayDate said:
Also .....his "throttle range" at present is 600-2000 rpm under load. So I seriously doubt that he would see any major difference in fuel pressure over that range especially since the injectors don't appear to be calling for more fuel. If fuel pressure was dropping over that range......I would have a different conclusion.
Click to expand...
It's not whether or not the injectors are "calling for more fuel", it's the pressure behind the injector. That should be referenced to manifold, so if the manifold pressure goes down, the fuel pressure goes down. It's not the RPMs that make the difference, it's the throttle opening. If he was a 2000 with no load the throttle would be barely propped open and manifold pressure would still be very low, and should have a correspondingly-lower fuel pressure. At WOT, even at 2000 RPM, manifold pressure is essentially baro, so fuel pressure should be max.

ttmott said:
But, the data shows his MAP at atmo. So even at 2000 rpm his fuel pressure should be max; whatever that is. Regardless, the fuel pressure as long as it is over 30 psig should support any RPM condition. The ECM will compensate the injector pulse rate to achieve a throttle position / RPM.
Click to expand...
If the engine is running lean, due to the loss of fuel pressure, how much HP is it losing at 2,000 RPM? How much does it really need to get over the 'hump' and up on plane? How much "excess" HP does the engine have in this range where it can afford to lose some? How does the ECM compensate for this loss of pressure (or even 'can it?'). ?
 
km1125 said:
These two posts don't make any sense to me:


It's not whether or not the injectors are "calling for more fuel", it's the pressure behind the injector. That should be referenced to manifold, so if the manifold pressure goes down, the fuel pressure goes down. It's not the RPMs that make the difference, it's the throttle opening. If he was a 2000 with no load the throttle would be barely propped open and manifold pressure would still be very low, and should have a correspondingly-lower fuel pressure. At WOT, even at 2000 RPM, manifold pressure is essentially baro, so fuel pressure should be max.


If the engine is running lean, due to the loss of fuel pressure, how much HP is it losing at 2,000 RPM? How much does it really need to get over the 'hump' and up on plane? How much "excess" HP does the engine have in this range where it can afford to lose some? How does the ECM compensate for this loss of pressure (or even 'can it?'). ?
Click to expand...
Engine torque is directly related to the air/fuel ratios. Too rich and no power too lean and no power. Moving a fuel mixture from a normal Stochio mixture to lean the power will go up then fall off like a cliff. An EFI lean condition will usually cause the engine to stumble which he isn't seeing when he hits that 2000 RPM wall. So I'm re-thinking the duty cycle thing.
 
km1125 said:
These two posts don't make any sense to me:


It's not whether or not the injectors are "calling for more fuel", it's the pressure behind the injector. That should be referenced to manifold, so if the manifold pressure goes down, the fuel pressure goes down. It's not the RPMs that make the difference, it's the throttle opening. If he was a 2000 with no load the throttle would be barely propped open and manifold pressure would still be very low, and should have a correspondingly-lower fuel pressure. At WOT, even at 2000 RPM, manifold pressure is essentially baro, so fuel pressure should be max.


If the engine is running lean, due to the loss of fuel pressure, how much HP is it losing at 2,000 RPM? How much does it really need to get over the 'hump' and up on plane? How much "excess" HP does the engine have in this range where it can afford to lose some? How does the ECM compensate for this loss of pressure (or even 'can it?'). ?
Click to expand...

If you are trying to make the case that 37 psi of fuel on the fuel rail is the issue why his engine won’t go beyond 2,000 rpm…..just state it.

The OP has replaced all the components between the fuel rail and the tank and 37 psi is more than enough pressure to fuel the injectors well past 2000 rpm. 10% more fuel pressure in my opinion, isn’t going to make much of a difference if the injectors are not staying open longer.
 
As firmware engineer, if this thing is stopping exactly at 2000 rpm every time and all the sensors check out, the controller needs to get swapped out.
I can see the pseudo code in my head:
if (sensorAgood & sensorBgood & sensorC.....)
maxRPM = 4500
else
maxRPM = 2000

Before Hoplite's brain explodes should we start a gofundme and get him one?
 
ttmott said:
Engine torque is directly related to the air/fuel ratios. Too rich and no power too lean and no power. Moving a fuel mixture from a normal Stochio mixture to lean the power will go up then fall off like a cliff. An EFI lean condition will usually cause the engine to stumble which he isn't seeing when he hits that 2000 RPM wall. So I'm re-thinking the duty cycle thing.
Click to expand...


You are over thinking this tech. Your Dominator system relies on a wide band O2 sensor to control the a/f mixture and is able to learn from it. This antique has a fuel table, map, tps and coolant temp to work with.

Based on the internal table it should be increasing Injector On. If fuel pressure was low we still should see Injector On increasing based on MAP, spark advance and TPS. We don’t so…..why?
 
northshore said:
As firmware engineer, if this thing is stopping exactly at 2000 rpm every time and all the sensors check out, the controller needs to get swapped out.
I can see the pseudo code in my head:
if (sensorAgood & sensorBgood & sensorC.....)
maxRPM = 4500
else
maxRPM = 2000

Before Hoplite's brain explodes should we start a gofundme and get him one?
Click to expand...
I'm sending him one.
 
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