F150 Surging at Constant Speed

[fordgirl]

I guess I will try to tackle one symptom at a time since I believe I have multiple problems...

TRUCK: 1995 F150, 351W, 2WD, 241k

PROBLEM(S): While driving, acceleration seems to be fine but if I try to hold a steady speed (35mph usually does it), I can feel my truck shudder, no CEL.

CODES: KOEO: 111, CM: 211, KOER: 111

MAINTENANCE DONE: Replaced distributor, checked wiring, rotor, cap for signs of arcing, reset engine timing to 10 degs (stock), cleaned MAF sensor, replaced air filter, changed oil, replaced TPS and cleaned the throttle body.

Any help would be GREATLY appreciated!!

 

[O'Rattlecan]

This sounds to me like a fuel pressure problem. Does it idle well? Perhaps it can't keep enough pressure up at cruising speeds when consumption is high, but has enough life left in it to idle okay.

Ryan

 

[fordgirl]

IDLE

Yay! Maybe we are getting somewhere. It does NOT idle well. Another symptom is the following:

When I start my truck (hot or cold) about 90% of the time within 1 minute of being on, the engine will rev up to 2000rpms with the CEL flashing 4 times, then almost stall and settle down at around 800rpms. I have also noticed that if I give it gas when it is revving, it starts to stall.

Normal idle is also not ideal.

I had this idea as well and previously I had checked the vaccuum hose coming off the top of the fuel pressure regulator (no wetness found). However, maybe something else is causing the fuel pressure to have problems? Any ideas on what to check/take apart/replace/clean?

Thanks for the help!

 

[O'Rattlecan]

Try to measure the fuel pressure at the fuel rail on the truck while it's running.

Ryan

 

[Killians92-4.9]

Could be idle air control valve, that was causing my 92 to surge at idle, and surge at lower speeds while driving but my truck would also throw the CEL very randomly then clear itself, could also be a simple fuel filter too

 

[fordgirl]

Next steps

Thanks for the advice guys. I will check fuel pressure, idle air control valve, and fuel filter when I can get my hands on the tools. I will post results. Thanks!

 

[fordgirl]

Bigger problem

Truck wouldn't start today, 3rd time in last couple months. I started it with a screwdriver. Bad starter selenoid or related to these problems do you think?

 

[fordgirl]

IAC valve good

I have a multimeter so I checked it. Passed voltage test from PCM (12V) and resistance test across pins (11.3ohms)

Next up fuel pressure when I can get my hands on the gauge.

 

[5.0Flareside]

No start do to solenoid and surging isn't related.

Fuel pressure is very likely on the surging.

 

[fordgirl]

No Start

My question is more asking... if my truck doesn't start but does start with a screwdriver (and this only happens at most once a month) does that automatically point to a bad starter solenoid? Or could there be another cause? I feel like it would be happening more often if the solenoid was actually going bad.

 

[O'Rattlecan]

Flatly, if that starts the truck in a no-start situation, it simply is the starter solenoid. No ifs, ands, or buts about it! You've isolated the problem and that work around solves it.

Ryan

 

[fordgirl]

Bad Starter Solenoid

Alright. I will replace the starter solenoid. Thanks!

 

[fordgirl]

Fuel pressure NOT GOOD!!

I bought a fuel pressure gauge and tested it at the test port on fuel rail. Engine off is 20psi and should be 35-45psi. Any ideas what to dive into first?

 

[O'Rattlecan]

Well it's either your fuel pressure regulator, or your fuel pump not delivering enough pressure. Glad you got it narrowed down!

Do you have one or two gas tanks? If you have two, that might be a way to see if one fuel pump performs better than the other. If you only have one, no big deal, it's just not as easy to trouble shoot.

I'm not sure where to check fuel pressure BEFORE the fuel pressure regulator.

Ryan

 

[Fellro]

What terminals on the solenoid are you jumpering from/to? If the two main lugs, solenoid is suspect. Little pin to battery side big pin, solenoid is fine.

On the surging, it is also something to consider that the TPS is failing. It simply operates on variable resistance, so if the contact of the wiper to the resistor is not good, the resistance will vary, which tries to tell the computer you are moving the pedal, which will make for surging.

 

[fordgirl]

I have 2 tanks and I was actually confused on If that means I have 2 pumps. Fuel pressure regulator shows no obvious signs of failing, no fuel in the line. I was going to change out fuel filter for a starter, it hasn't been done in a long time. I will check pressure of the other tank for comparison. Thanks!

 

[fordgirl]

I was jumping the two main terminals. I ended up replacing the starter relay but I am not happy how the new universal one (has 4 terminals, I don't need the 'I' one) fits.

I had already suspected the TPS in the beginning and I replaced it and cleaned the throttle body with no improvements.

Thanks for the help!

 

[Fellro]

On your year, there is a pump per tank. If you notice a problem on one tank, but not the other, it can be a pump issue. If it is exactly the same no matter, then I would look elsewhere. Fuel filter really should be the first thing you look at for something like this. Low pressure often can be related to a restriction in the supply. The pumps will only pump to a certain pressure before they max out. If the filter causes it to restrict, the pump will be maxed out, but the line pressure at the motor will be lower.

 

[fordgirl]

Fuel filter was removed and seemed perfectly fine. New fuel filter installed with no change in performance. Fuel pressure is now 20psi at KOEO (35-45psi) and 30psi at KOER (30-45psi).

 

[O'Rattlecan]

So did you say both tanks were making the truck run equally crummy?

Ryan