Hey everyone, I'm new here so please help me. I've got a 1989 Ford F150 with the 4.9 liter big 6 with a standard tranny, and it starts great and idles fine but when your accelerating in any gear it sputters. I've put a new air filter, pcv valve, fuel filter, plugs and wires, cap and rotor, checked all electrical connections, and just about pulled my hair out. It has 160,000 miles on it and is in great shape. The timing doesn't bounce at all and doesn't burn or leak any oil. A friend of mine has the same truck but with an auto tranny, and has the same problem. He has had it to 2 different dealerships and it still does it. Does anybody have any clue as to what causes this and how to fix it???? PLEASE HELP ME and I'll even buy you a beer.

 

Any check engine lamp on?
There are several areas that can cause action this way.
Ignition, fuel and egr, MAP.
Some troubleshooting has to be done to find the faulty system.
Things to try are hook up a timing light and try to see an ignition miss above idle.
Test fuel pressure.
Disconnct the EGR and plug the hose for test.
Inspect the MAP sensor hose for defects.
Once the ofending operation is found then the specific fault have to be looked for.
Wire harness and plug faults can also be a problem.
There is a simple code reader (about $30) to use for both codes and engine running testing, wire wiggle testing, cylinder balance testing.

 

Any check engine lamp on?
There are several areas that can cause action this way.
Ignition, fuel and egr, MAP.
Some troubleshooting has to be done to find the faulty system.
Things to try are hook up a timing light and try to see an ignition miss above idle.
Test fuel pressure.
Disconnct the EGR and plug the hose for test.
Inspect the MAP sensor hose for defects.
Once the ofending operation is found then the specific fault have to be looked for.
Wire harness and plug faults can also be a problem.
There is a simple code reader (about $30) to use for both codes and engine running testing, wire wiggle testing, cylinder balance testing.

 

Thanks man, I'll look a little closer at these areas and let you know if I find the problem within them...

 

Does it sputter out the exhaust, or fire back through the intake? Also, does the problem get worse as the load increases? Does it do the same thing accelerating downhill as it does uphill? When did the problem start? Did it start out bad and stay that way, or did it gradually get worse with time? Does it have the original timing gears? Has anything been done right before you noticed a problem that may have removed a ground wire to the frame or firewall? Can you recreate the problem sitting still ,or does it have to be driven under load? Did you start getting gas from a different place recently? I know you said your engine doesn't burn or leak oil, but it is definitely full, right? Have you checked for any broken or disconnected vacuum lines? Fuel pump pressure? Fuel pump volume? Fuel pressure regulator? Coil failure under load?

SL

 

Intake leak. I had a 85 F150 and it would idle great and would drive okay if I barely got into the gas. If I gave over 1/4 gas it would sputter and back fire through the carb. I ended up rebuilding the carb and finally had the dealership find out it was an intake leak. I was 16 at the time and didn't know jack about engines at the time.

 

I had a 91 f150 with the 4.9 and had the same problem. It tuns out the fuel pump was the problem. When idling the engine ran fine. As soon as you gave it some gas it would sputter. At idle the fuel pump would supply enough fuel and pressure to keep the engine running, above idle it would sputter. Unfortunate for me it took 3 days and alot of parts changing to find out the pump was on its way out.

Hope this helps.
Mike

 

i own a 94 F150 and before i got it i was told a little of the history. It has a straight six. It too had a horrible problem, it couldnt run worth anything. At idle it was ok, but once given some gas it couldnt do jack. Im not sure if it was a common problem or not, but sure enough it was the fuel pump. It's a fairly spendy fix, (due to internal pumps in tank(s) yet fixed it. now it runs like a champ.