1999 454 Mag MPI just quits - videos

[douglee25]

The process needs to be done with engine running and hot.
Back in the day - to set the butterfly base opening, we used a specific size drill bit as a "feeler gauge" and that was done with the Throttle body removed.

I guess I'm missing something. Aren't we trying to set the base opening and then rerun the IAC calibration procedure?

 

[ttmott]

I guess I'm missing something. Aren't we trying to set the base opening and then rerun the IAC calibration procedure?

IAC "calibration" is done with the throttle body butterfly adjustment. For example as the throttle blades are opened the ECM reduces the IAC duty cycle to set the desired engine idle RPM. The ECM is the only thing that can set the IAC base.

 

[douglee25]

IAC "calibration" is done with the adjustment of the throttle body butterfly adjustment. For example as the throttle blades are opened the ECM reduces the IAC duty cycle to set the desired engine idle RPM. The ECM is the only thing that can set the IAC base.

OK, so why not do this adjustment using the cable and test the entire theory. If it works, great. You can take it apart and adjust the throttle blade with the set screw later.

 

[PlayDate]

OK, so why not do this adjustment using the cable and test the entire theory. If it works, great. You can take it apart and adjust the throttle blade with the set screw later.

While you can open the throttle blade with the cable you are also increasing the TPS signal and at some point the ECM is going to get confused. That's why if you can get a tool to reach the adjustment screw .....you can solve the air bleed problem.

If you just want to test the theory.......you can put a .005 feeler gauge between the throttle blade and the throttle body. What you don't want to do is have whatever you are using to hold the throttle body slightly open get sucked into the engine.

I had a friend use a drinking straw and he was so excited that the engine was idling that he opened up the throttle and the straw disappeared.

 

[douglee25]

I like your suggestion, however, I believe the TPS moves whichever way you decide to open the throttle blade - screw, cable, or tool.

 

[ttmott]

I like your suggestion, however, I believe the TPS moves whichever way you decide to open the throttle blade - screw, cable, or tool.

The TPS idle voltage, throttle blade position, and IAC duty cycle baseline all need to occur simultaneously.
This isn't that complicated. Locate the throttle stop wherever or whatever that is. Use it to open or close the throttle body blades until the IAC duty cycle is where you want it (around 20 percent duty cycle). At the same time watch the TPS voltage and take actions to adjust it within spec. If I remember correctly the TPS voltage should be 0.5V plus or minus at hot idle. If it is greater than 0.65 volts the ECM will exit idle mode and start modulating the fuel flow. It's a bit of a short iterative process. The engine must be running and hot (meaning the thermostat has opened) to do the IAC setup. If the engine is not up to operating temperature the ECM via the coolant sensor will enrichen the fuel mixture and open the IAC for more air (ie high idle). The only fly in the ointment may be the ignition timing if the IAC is way out of spec. Usually the IAC can be set without messing with the ignition timing advance.

 

[douglee25]

The TPS idle voltage, throttle blade position, and IAC duty cycle baseline all need to occur simultaneously.
This isn't that complicated. Locate the throttle stop wherever or whatever that is. Use it to open or close the throttle body blades until the IAC duty cycle is where you want it (around 20 percent duty cycle). At the same time watch the TPS voltage and take actions to adjust it within spec. If I remember correctly the TPS voltage should be 0.5V plus or minus at hot idle. If it is greater than 0.65 volts the ECM will exit idle mode and start modulating the fuel flow. It's a bit of a short iterative process. The engine must be running and hot (meaning the thermostat has opened) to do the IAC setup. If the engine is not up to operating temperature the ECM via the coolant sensor will enrichen the fuel mixture and open the IAC for more air (ie high idle). The only fly in the ointment may be the ignition timing if the IAC is way out of spec. Usually the IAC can be set without messing with the ignition timing advance.

Tom - I understand all this.

The point I'm trying to make is, there's no reason he has to break the gaskets on that motor to run this test. Go adjust the throttle blade opening using the cables at the shifter (or wherever he has the easiest access) instead of the screw on the throttle body.

 

[ttmott]

Tom - I understand all this.

The point I'm trying to make is, there's no reason he has to break the gaskets on that motor to run this test. Go adjust the throttle blade opening using the cables at the shifter (or wherever he has the easiest access) instead of the screw on the throttle body.

So the hard stop isn't accessible unless the TB is removed? That doesn't sound reasonable for this type of setup....

 

[ttmott]

So the hard stop isn't accessible unless the TB is removed? That doesn't sound reasonable for this type of setup....

 

[370Dancer]

Not impossible, but downright inconvenient. TPS adjustment even worse. facing down. this is what I meant about devising some special tools to get access while in place. Off to get scans this am, and then maybe back on it this afternoon. I also found the OSO explanation of the relationships between these sensors and controls. The hex on a flex is the tool I need to assemble.

 

[Bill Curtis]

Will these work?

Amazon.com

 

[douglee25]

Is that thing running yet?? ☺

 

[370Dancer]

Is that thing running yet?? ☺

Patience, Grasshopper. Uncle Joe is moving kinda slow.......
Built my 1/8" socket driver last night. Waiting for a decent hour to fire them off this morning. I can reach the secondary throttle stop without removal of anything (barely).

 

[douglee25]

Dang. I'm glad to see you're pressing forward. Looking good.

 

[370Dancer]

Update:
Messed around with the strategy of adjusting the throttle body secondary idle stop screw to get the IAC to be 40 counts, while the TPS is reading 0%, while the engine is idling warm. I could take the IAC to zero, OR, nearly full, and setting anything in-between, it just hunted around by 500 RPM or so. Fearing that I did not clean the Throttle body when it was off, or that the yard boys had "adjusted" these, I chose to stop, pull the Plenum for the 100th time, and work my way forward again.

What I found, is that the primary idle stop was completely out of the picture by an 1/8 of an inch (yard boys), and I also discovered that the secondary moves both butterflies, not just the secondary, so I think the OSO procedure is flawed in its assumptions. Looks like I did clean the TB and butterflies, but I will do it again since it is off.
Plan is to figure out some kind of flex shaft tool that I can re-assemble with the plenum that will allow me to adjust the primary. This may, or may not be possible. If not, then it's going to be adjust, assemble, test, disassemble, adjust, assemble, test...... If I was I/O's, or straight inboards, I could do this by shimming the butterfly while running. Unfortunately I can't, unless I just leave the flame arrestor off until I am done, and then pull it one more time. Actually, maybe I could do this, and when I have the correct gap, pull it and set the idle screw once. Not sure that will hold though once cam pressure is on the screw.
I am consulting with Innovation Marine, who built the port short block, and they think I am on the right path.

 

[ttmott]

I'm thinking that tweeking the secondary butterfly for IAC duty cycle won't affect with the TPS.

 

[douglee25]

Interesting.

 

[370Dancer]

Tactic for this am. Plug the throttle body in to the harness by itself. Set the primary idle screw to get the correct TPS volt/percent. (ignition on, no start). Put it together and see where I am. If any adjustment, do it on the secondary knowing it will move both butterflies. Head for IAC value of 20-40 counts, with no hunting. Wish I could find a factory guy who set these for a living. The guy below is as close as I'm going to get.

Advice from Innovation Marine, who build/see these every day.

"Sounds like you are on the right track then and I don’t know that we could help more than what you are doing. I mean in theory start with closing the throttle blades with the stops you mentioned then set the TPS, make sure it is zero (and the throttle unhooked as you mention) and reading the voltage the sheet says. Then usually you would fine tune it with the primary stop (some bigger engines can be tough or if you have something changed from stock like on bigger engines that the IAC is not big enough we used to have to drill a hole in the throttle plate to let enough air in without moving the TPS off zero. Remember the minute the TPS comes off 0% you have lost it has to be 0 and most are not adjustable. So follow the correct path:

1. Zero the TPS which should make the throttle blades closed or at least what the manufacturer considered closed (unless it is adjustable).
   1. In theory if nothing else is changed it will be back in the correct place.

1. If the TPS is adjustable you may have to play with where 0 is to get where you need to be."

My TPS is non-adjustable.

Happy Friday.

 

[douglee25]

The one butterfly that doesn't have the idle stop touching, is the throttle blade closed? It looks more closed than the other.

 

[ttmott]

In this order -
Adjust the TPS with the primary butterfly stop screw - engine does not have to be running to do this.
Adjust the IAC with the secondary butterfly stop screw - engine does have to be running and at operating temperature to do this. I'd set the IAC as low in the duty cycle as possible.

Again, adjusting the secondary butterfly should not change the TPS zero.