1994 F150 4.9. Is missing real bad.

The truck start and idles fine. Get on gas pedal very slow it muved ok, get a little more gas and it start missing so bad that it can't be driveable.The same thing on park.
This it's what I has done so far:

New spark plugs, plug wires,distribuitor cap rotor,new fuel filter:
Timing-Check
Vacum leak- Check.
Cylinders -Check(Pulling plug wires).
At this point I have no clue where to look next. I will appresiated any help. Thanks

 

Welcome to FTE.............


EGR valve stuck open???

 

fuel pump , check the fuel pressure !

 

I will check the fuel pressure & test the EGR valve and post the findings.Thanks

 

ok Im gonna go out on the limb here as no one else has yet and risk breaking the branch and landing in a hen house of angry hens just before christmas dinner and ask...did you pull any codes yet? usually if the engine is missing there is most likely (not always but a good chance) for CEL (Check Engine Light) codes to be stored (even if your CEL isnt on there could still be codes stored), in your engine bay (this is an OBD1 truck) there is a plug on the driver side fender near the hinge that should say something along the lines of EEC test or something like that, someone may hopefully chime in with the diagram of the pins to jump with the names written on it, but you need to jump the test lead and I *THINK* #1 lead (far right on the 4 or 5 pin plug).

better way is to get the Equis (sp?) 3041 or similar OBD/CAN/OBD2 reader and pull the codes like that. if you can tell us what codes (if any) are being given we could further diagnose whats going on as this is one of the many issues you could throw money/parts at and never fix if your not diagnosing the correct thing....


so please get us some codes first before throwing parts and money at the issue....

also on a side note, Jorge, Welcome to FTE or if you prefer español, Bienvenido a FTE!


PS if you want me to translate this/transpose any of this into español for you let me know and I will try my best to do so and I will either do this VIA PM or with english translations on the boards , again WELCOME TO FTE!!!

 

I just scan for codes and there none codes store. The truck still idle just fine but ones I step on the gas it start missing very,very bad.
I don't know is this will help, but went I was changing the fuel filter I pull out the fuel relay & when to the fitting on the fuel rail to release any pressure left in the line but was no pressure, no even a little spray. Anyway thats all I got for now. Any ideas? Thanks

 

did you or anyone mess with the plug wires, are they crossed properly to each other? are any crossed that shouldnt be? did you follow the diagram on the cross member for the wire routing? sounds like we could have possible cross detonation happening if some wires got miscrossed...

this is what you should see:






also did you check fuel pumps for both tanks to see if maybe they were bad?

 

The firing order is good (1-5-3-6-2-4) No cross firing.

 

ok but did you ensure the wires were routed as shown in the diagram on your truck? order doesnt matter at all if your plug wires are incorrectly crossed as there is a cross detonation issue with these things, dont know why or what but its there...

 

You might want to drop the exhaust before the Catalytic converter. I seem to remember a problem with the early 90's 4.9L. But I think the exhaust restriction was caused by another issue.

 

Can I rule out ( for now ) the fuel pump since the truck has two fuel tanks and starting missing with both of them at the same time?.

 

OK; Test the fuel system: (New fuel filter)
A. "Key on engine off"
1) Front fuel tank: 52 PSI hold pressure for 1 minute.
2) Rear fuel tank : 38 PSI drop to 32 PIS in 1 minute.

B. Engine running: Both Fuel tanks 48 PSI. While apply Throttle gauge bounce between 47 & 48 PSI.
C. Engine running: unplug vacuum line from pressure regulator, gauge move from 48 PSI to 58 PSI.

It looks like the fuel pressure regulator is working properly.
The rear fuel pump seeings to be bad.
But how about the front fuel pump? It read 52 PSI! But the truck still missing real bad.

 

at the moment thats possible

 

I check the for exhaust restriction but but there is none.

 

Throwing out ideas here...

Bad PIP from the distributor? I think if it were bad, the truck will idle but perhaps the TFI is having problems getting signal from the PIP. RLA2005 knows more about this than I do. May want to wait and see what he thinks.

Also, something that get's overlooked, when you checked timing, did you check to see that the Timing was @ 10BTDC and then when you plugged the Spout connector back in, that it advanced? If the timing isn't advancing correctly, then this can give you the same symptoms.

Also, it sounds like exhaust restriction like another member suggested, but you said that you checked this.

Clogged injectors also another idea.

All I can think of, except for a kinked fuel line or a return fuel line.