I have an '88 F350 351 fuel injected. The problem is that it stumbles all over itself when accelerating and surges a little at an idle. It idles fine cold or hot except for the little surge. Plugs, cap, rotor, coil & fuel pump(on frame) all new. Haven't been able to pull codes, I'm 20 miles from town and not sure it will make it there. It also has an MSD 6A box and I've also checked for vaccuum leaks and there don't seem to be any. Could this maybe be my in tank pumps? I know the rear one doesn't work, which explains the syphening to the front tank. Open for suggestions.

 

I am betting it is the TPS. Or maybe the IAC, some peaple over look the IAC, but if it is sticking, you will get extra air entering the intake at idle causing a surge, and you will get way to much air during acceleration causing the stumble.
How did you check for a vaccuum leak? The best way is to take a can of brake clean or starter fluid and spray it aver every inch of your intake system, including the vaccuum lines.
Don't forget that your heater controls are also powerd by vaccumm, so is your brake booster (you may hear a hiss when stepping on the brake) disconect your heater control vaccuum line and plug it, do the same with your brake booster and see if the surge goes away.
I hope this helps, just throwing out all possible problems based on the symptoms described.

 

Explaine "the syphening to the front tank".
Do you mean the front tanks fills while on the rear tank or what but you said the rear does not work????

 

Mr Finch-Yes, I did my vaccuum test with a can of brake clean. Any tests to check for the TPS or IAC? and will they trigger the check engine light to come on(it hasn't come on so far)?
subford-yes, I meant the front tank fills while on the rear tank.

 

Did you check the heater control supply line to make sure you do not have a leake under the dash?
The electrical book I have is for the 1996 models, but the principals are bassically the same, the wire colors may be different.
There should be 3 wires at your tps. According to my book the GY/R wire is the power, The BR/W is the ground, and the GY/W is the signal wire. With the key on, Back probe the GY/W wire and slowly pull the throttle cable, the voltage should slowly go up. At about half throttle it should read 6 volts, at fully open it should read around 12 and at closed throttle it should read around 0. If the readings are way off, jump around, spike, or don't move at all then it is bad.

 

With the tps, what ever percentage you have the thottle open, you should be reading that percentage of the battery voltage.
EX. A battery at 12 volts with the throttle open 1/4 you should read 3 volts, if the throttle is a 3/4 you should read 9 volts and so on.

 

I didn't check under the dash (didn't think of that) and I'll go check the TPS right now and get back to ya

 

As I stated earlier, you should have atleast one vaccuum line going through the firewall, just diconect that and plug it, see if your surge stops. IF it did not make a difference then you lines under the dash should be good. do the same for the line going to the Brake booster. These are simple checks that take only a few seconds.

 

I checked for leaks on the brake booster and the heater, all seems well. I forgot to mention the idle surge seems to go away when it gets warmer. But on th TPS, I got .08 closed, 2.4 at half, 4.3 at WOT. Sounds like we might be on to something if i did my test right

 

The TPS should be about 0.9 VDC with a closed throttle and about 4.5 VDC WOT.
I would doubt that you got .08 and more likely 0.8 Volts. So the voltage should be OK at the TPS.
The reference voltage from the computer to the TPS is 5.0 VDC so you will never have anything higher than 5.0VDC.

Sounds like you may have a bad selector valve and that is why the front tank fills.
However that would not cause your surging problem as it would be return fuel from the engine filling the front tank.

 

I'll be heading to the parts store fist thing in the morning. Would this cause the stumbling & bucking under load? Is it possible that i have more than one problem? (in tank fuel pump) Thanks for all the input!

 

What are you going to buy at the part store?

 

Not sure now ( ha ha I was posting that when yours came through) I guess my TPS is reading normal then (you were correct .8 not .08) Thinking both in tank pumps might be bad at this point. Any test ideas for those?

 

Unhook the supply fuel line (the larger of the two) from each tank at the selector valve one at a time and aim it into a 5 Gal bucket.
Unplug the high pressure pump on the frame as it will not be getting any fuel for cooling.
Short pin #2 to pin #6 of the EEC self-test connector and tun on the key.
The selected pump should run a steady steam of fuel at 5-7 PSI into the bucket.
You can check the PSI with an old type fuel pump vacuum gauge.
The selector valve needs 4-5 psi to change to the other tank.

 

Your fuel system:





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