How do the valves look? Any of them stuck open? Could you tell if anything was loose when you took the valve covers off? How are your spark plugs and wires?

 

Go basic first...

Check compression in each cylinder. What are the readings? 120-150 psi or so, but all within 10 to 15% of each other?

You mentioned that you have no vacuum leaks, but what is the vacuum being pulled by the engine? Steady and in the range of about 16 - 22 in?

 

Plugs and wires are new. All valves close.

I took it to the stealership for a diagnosis: They said there were codes for injector 4 and 8. I never had those, I had different ones, they said a compression test was needed and wanted 2 hours worth of time. I said... NO and brought it home and did a compression test. All cylinders checked out at 149-155 PSI. Thats good news.

I also replaced injectors 4 and 9, cleared the codes and the codes did not come back. Idle still bad.

So I finally went ahead and got up there with it running and started wiggling cables. When I got to the MAP I unplugged it and the engine started running 90% better!

So a bad MAP caused all of this it seems. With the MAP unplugged it idles much better but shows misfire blinking light on dash and revving is lagged, this is probably normal?

I picked up a new MAP sensor at Autozone and the thing is close to being correct. The part I got has two bolt holes, but the sensor in my truck does not, it twist locks in. Are these two interchangeable? I plugged it in and set it in place but it did not seem to help things run better.

 

Yet another update:

Replaced MAP: With new MAP it runs just as bad as with the old MAP so I suppose the old MAP was not bad. With MAP disconnected it runs slightly better.

I went down and had the cat replaced, with 0 improvement. Bummer...

I think I have ruled out about everything?

I am down to the ECU maybe? On the way back home the TB stopped responding briefly, the brake light lite up and the RPM gauge went wacky.

The best way I can describe it currently:

Wont really idle, if I disconnect the MAP it will idle a bit but not too good. When driving below 2000 RPM it stumbles and lacks power, once it reaches 2100 or so it smoothes out but still nowhere near full power or smooth. If I put it in neutral at a light I have to keep my foot on the gas and it surges ever couple of seconds.

At the end of the rope, this truck is possessed. Any help so very appreciated.

 

Have you taken off the throttlebody and checked it out? Also check fo a short it the MAP sensor wires, maybe something touched the block and burned through?

 

I replaced the TB with a brand new one and it made no difference (returned it and cleaned the old one).

Any easy way to test the MAP sensor wires?

 

Did we go over the cam and crank sensors

 

I do not know if the MAP sensors are interchangable. I thought I have read from some other threads here before that there is a plastic tab on one of the MAP sensors that keeps it from being used in the wrong application. The tab interferes with a spot on the intake manifold, if I remember correctly. I do remember that the MAP sensor on mine, which is also the twist-in type, felt like it was loose as I took it out and re-installed it. For a part that holds vacuum that seemed strange. In my case, it wasn't the MAP, mine was a broken valve spring like many others have had happen on '03 5.7 motors.

That is good news about the compression.


Have you tried to check the fuel pressure? Check for 45 +/- 5 psi while running (or something close to that anyway, don't remember exactly). Then watch for any leak-down on the fuel system after you shut the motor off.


Vacuum pressure...? You can often tell a good deal about what is going on from the way a vacuum needle moves.

 

No but wouldn't they throw a code? On my audi they sure did

 

^Not necessarily. Those sensors do some weird stuff.