Swapped out mlps, no change. Went back to starter and got a new one. Truck started with new one, so I guess just getting it out and over to oreillys unstuck it enough to test fine over there.



So, back to original problem -

Idles like a rock star, stumbles and dies off idle with throttle input. Before it dies, I get a rich condiition, and a cloud of black smoke before it cuts out. After cranking a few times to get cylinders clear, it starts again.

 

Well, tested the 02 sensor, MAP, IAT, EGR, knock sensor, restested TPS and IAC. Nothing

Tested fuel pressure, pumps are working. Holding 43 psi when running, 53 psi with the jumper in, car off. Test procedure listed in Haynes indicated the FPR wasn't working so swapped that out and no luck. Clamping both fuel lines resulted in loss of pressure, so it seems I have leaky fuel injectors.

If that doesn't solve the problem, I guess PCM is next. Which one should I buy? I looked on rockauto and they have a few Cardones and a couple Standard motor products listed for the 4.9L E4OD. Which one? Or should I be looking elsewhere?

 

Fuel psi @43 seems low for the 4.9. Should be minimum of 45 and mine is around 48-50. Now, I won't dispute some variation, but if the high psi check valve in the pump is bad, then this can cause problems as well. When you blimp the throttle, does the psi go up? If not, then pump is weak.


If you have to lightly go into throttle to keep it from dying, then it sounds like low fuel psi or clogged exhaust.

Are the original cats on the truck? Chance's are one is melted or plugged.

As far as the PCM goes, you need to pull it and visually inspect it! In fact, you may do more harm than good as some if the refurbished models have seen far better days and may only cause you more problems. Don't lighten you wallet any more until you get a better idea on fuel psi.

 

It goes up a little. it is low in the range (although I think 43 running is actually out of range low), but everything we did to test fuel pump (according to Haynes) indicates the check valve and pump are good.

Our test for leaky injectors was to block off both fuel lines and see if pressure dropped (it did). So my assumption is that the leaky injectors could be causing the low pressure.


The reverse actually. It idles fine and stays running, until you give it throttle. it dies when throttle is added. And the exhaust has more holes in it that swiss cheese, so it's pretty free flowing if not through the path it's supposed to go

For sure, I'm not ready to buy one. I'm just trying to be sure that if I do need one, I know what to get.


Thanks for the help and thoughts, I've tested so much with no joy, I'm running out of options. Tuesday I'll get the injectors out and try to clean them. I ordered some new ones as well because rockauto has a closeout on the motorcraft ones ($25/each) in case cleaning doesn't work. If cleaning does work, I'll return them.

 

Cleaned injectors today, and then found the source of the problem. The charcoal canister is sucking fuel from the tank and dumping it into the throttle body.
I traced the line to the fuel tank to the top of the tank and didn't feel any valve or anything, I assume there is one in the tank? Should it be hanging down into fuel? My truck has less than a quarter tank in it, but that vapor line pulls liquid fuel.

Good news is, simply plugging those ports on the top of the TB makes my truck run fine.
Very weird though

 

It sounds like you might have found your problem, but the symptoms you described were exactly like my 94. Idles fine, but has a hard stumble on first acceleration and dies in reverse (almost every time). My problem was the gasket at the throttle body. I replaced it and the truck runs excellent. It solved both the dying in reverse and the hesitation. Here's a picture of what my old gasket looked like. I had replaced it several years back with a new Fel-Pro gasket, which was very thin. This time, I cut my own gasket from a roll of gasket material I already had. It is thicker. We'll see if it lasts longer.

 

yikes, not much gasket there.

I replaced the TB gasket once I got the intake manifold off (cleaned the TB too) to access the fuel injectors. Haven't tried the forward-reverse-forward since. Right now I have the canister off and drying out, with the ports on the TB capped off.

 

Good to hear you replaced it. Hopefully all will be good when you get it back together. I'm not sure why it would be pulling fuel.

 

There should be a plastic vent on the top of the fuel tank, that the charcoal canister lines go to. I forget if it's a check valve or not, but it definitely should not pull fuel, only vapor.

In this photo, it's the white plastic piece on top of the fuel tank. The line that goes back to the canister isn't in the photo, I was in the process of installing a new one.

 

great, thanks for the photo. Guess I'll be dropping the fuel tank next so I can see what's going on.