I am reviving my 1988 F250 with a 300 inline 6 EFI, 4 speed manual tranny, 2 wheel drive. The truck has been sitting for some time but when I put a hot battery on it it cranked right up. The problem I am having is when I am driving it and say I am in 3rd gear and mash it to the floor it spits and sputters and jerks like it is missing. I attached my fuel pressure gauge and started the truck when it was cold; vacuum line connected to FPR (Fuel Pressure Regulator) 55 lbs., vacuum line NOT connected to FPR 59-60 lbs. Truck seemed to run fine for ABOUT 40 minutes then down shift to 3rd and floor it and it's acting up. I left the gauge connected to the fuel rail schrader valve so I pulled over and checked the pressure and I was slightly fluctuating between 49 and 50 lbs. It seems to me I do not have a fuel problem, just my opinion.

I am thinking I may have an electrical problem and electrical problems are really over my head so any and all help is greatly appreciated along with any other ideas you might have. I am kind of leaning toward MAYBE the pick up coil is breaking down or the ICM maybe........ Honestly I don't know and would appreciate any help you gentlemen can give me, Thank You.

I forgot to mention I installed new plugs, plug wires, rotor, and distributor cap, changed the oil and filter, new fuel filter, new air filter and crank case breather filter.
Probably wouldn't hurt to check the timing?? Thank You again for your help and input.

 

if you have 2 tanks does it do it on both, did you attempt to empty tank/s, after it sat, and use new gas, after driving, have you checked for codes, even if CEL isnt on, could have stored codes,

 

Thank you for your input. The truck has only the one fuel tank. I attempted to drain the old fuel out but there was only ABOUT 3 or 4 gallons in the tank so I just filled it up with good/new fuel, 19 gallon tank. I have not checked the codes, honestly I don't know where to hook up a code reader to check codes. I did try to check the timing earlier but my timing light crapped out, it couldn't decide if it wanted to flash or not or when it wanted to flash, I'll pick up a new one tomorrow. Again I thank you for your ideas and input.

 

under hood is the obd plug to check codes, driver side


pic courtesy of subford



what it looks like

 

Thank you sir I really appreciate it. I'll see if I can hook up my code reader tomorrow.

 

Update: Well I haven't found my code reader yet, we built a house a couple of years ago and moved so...... Any way I was still thinking about the fuel pressure even though it showed to be "normal". I built me an extension line for my fuel pressure test gauge and taped the gauge to the wind shield. I drove the truck normally for a few miles and everything looked good, about 54 lbs. of pressure. I then slowed down to about 25 mph, down shifted to 3rd gear and pressed the accelerator to the floor. The fuel pressure immediately started dropping about as fast as the speedometer was rising. When the pressure dropped to about 20 lbs the truck started acting up as usual. I let the accelerator up and the pressure rapidly came back up and the truck ran fine again. I did this 3 or 4 times with the same results each time. I am now leaning really hard toward the fuel pressure regulator. I still want to see if there are any codes in the computer but I've got to find someone with a code reader first. Till I find someone what are your thoughts about going ahead and replacing the fuel pressure regulator? Thank you for your input and help.

 

I would probably try fuel filter(cheaper) could have gotten gunked up, and when petal to the metal, it couldnt keep up, if you think regulator, dont let them give you a Standard PR-18 it is wrong one for I6, its operating pressure is 47psi, you need one that has operating pressure of 54-57psi.

see link below how to get codes, without reader
Fuel Injection Technical Library » How To Run a Self-Test

 

Thank you a million for the link to read the codes I really appreciate it and thank you for the heads up on the different pressure regulators, I'll certainly keep an eye on that IF it comes to changing the regulator. It sure can't hurt to change the filter, easier and cheaper too. Your idea about the filter being gunked up could certainly be spot on. A mechanic friend of mine told me he didn't think it was the regulator because the pressure increased about 4 or 5 lbs, at idle, when I unhooked the vacuum line.

 

You can use a paperclip to get the codes instead of a wire. Also your clutch MUST be depressed the ENTIRE time you are running codes. Sandy

 

Here is a good video to help you run codes. The 4.9 and manual are the only trucks that need the clutch depressed to get codes. You should have two digit codes and here is a list to indicate what they mean. Any problems just get back to us. Sandy
https://www.therangerstation.com/tec...gitcodes.shtml