power issue with 7.4L MPI V8 - need help

[emmafabre]

HI,
I have strange problem. just like this the engine does not want to go in the rpm when the gear is on and I push forward. It is ok unclutch but no gear on. in idel the engine does not run smoothly.
Strange also when I have the lever forward and try to acelerate 9it does not work) but if I play with the electrical switch for the leg I have some acceleration of the engine like if it would run as normal. strange.

Engine engineer told me to change the manifold and cost me a fortune but problem still here. I need help to troublesoot that.

My feeling is that's electronic issue due to the fact that playing with the switch ofthe leg make the engine changing the way to run immediatly.

please help

 

[emmafabre]

Re: power issue with 7.4L MPI V8 - need help

HI,
Just to avoid question.
- throttle cable is good and brand new
- spark plugs replaced
- oil and fuel filter replaced as well.


Still need you help to undertsand what is the source of the proble

 

[Bondo]

Re: power issue with 7.4L MPI V8 - need help

in idel the engine does not run smoothly.

Ayuh,... How about doing a Full,+ Complete Tune Up, rather than Just the plugs,+ filters...

but if I play with the electrical switch for the leg I have some acceleration of the engine like if it would run as normal.

What wires going to What drive,..??

 

[emmafabre]

Re: power issue with 7.4L MPI V8 - need help

Hi Bondo,
thanks for your answer but what is a tune-up? not sure to know what do you mean?

Regards
emmafafare

 

[Don S]

Re: power issue with 7.4L MPI V8 - need help

but if I play with the electrical switch for the leg I have some acceleration of the engine like if it would run as normal.

What wires going to What drive,..??

It has to be a Bravo drive, there was NEVER an Alpha drive on an MPI 7.4.
The only wires going to the drive are either the Mercathode, ground wires, or trim gauge sender.
None of which affect the engine.

Look at the top of this forum for the Adults Only or DIY sticy. Lots of info there you need to look at. Including downloading the OEM manuals for your engine and drive.

 

[emmafabre]

Re: power issue with 7.4L MPI V8 - need help

It has to be a Bravo drive, there was NEVER an Alpha drive on an MPI 7.4.
The only wires going to the drive are either the Mercathode, ground wires, or trim gauge sender.
None of which affect the engine.

Look at the top of this forum for the Adults Only or DIY sticy. Lots of info there you need to look at. Including downloading the OEM manuals for your engine and drive.

Hi Bondo,
for your infi, this day the engine engineer try to replace the fuel pump to see if it was the root cause of the problem but nothing change, Still no pwer in forward gear.
I really need help or idea for the trouble shooting.

 

[joncrisler]

Re: power issue with 7.4L MPI V8 - need help

This engine has a computer diagnostic port. You plug a diagnostic tool into this port and look for error codes. Your mechanic should check this out to see if there are any errors. You may or may not have error codes but procedure should be completed.

A tune-up is a term that indicates replacing parts normally done every few years. Spark plugs and spark plug wires, distributor cap and rotor, and fuel filter are some of the items that could be replaced during a tune up.

 

[emmafabre]

Re: power issue with 7.4L MPI V8 - need help

thanks for the help

tune up has been done, next step is the computer check.
I let you know when I have the result.

thanks so far for the support

 

[emmafabre]

Re: power issue with 7.4L MPI V8 - need help

compression have been checked and pressure is 135 to 145 on all cylender, thus it sounds ok.
tune up has been done
fuel pressure tested

still same problem: low rpm in forward gear the engine does not accelerate.

still need help guys.

only thing is I found that airbox is wistheling a lot but air filt changed and manfiold chaged as well.

HELP ME

 

[Bondo]

Re: power issue with 7.4L MPI V8 - need help

HELP ME

Ayuh,... It's kinda Tough,.... We're Mechanics,+ obviously, You're Not...
Read this list to your engine Engineer....
It's a comprehensive list of Reasons a motor won't pull rpms.....

 

[CharlieB]

Re: power issue with 7.4L MPI V8 - need help

The fact that there is a change in motor performance when the trim is used leads me to think that there may be a poor ground somewhere in the electrical system.

An EFI motor has a number of small grounds attached to the motor in a few locations, find them, disconnect, clean the terminals and the block to be sure that they have a good tight connection.

Same goes for the trim motor grounding connection.

Injector pulse width increasingly loads the ground connection, a poor connection would definitely impair power.