I have a 1996 4.9 lt, with 128,000 miles. During cold weather the truck will start properly. During hot starts or warm weather the truck was difficult to start. Recently, I had lost performance and noticed that the intake manifold was cracked. I just replaced the manifold and reset the onboard computer. While driving today the Check Engine light came on. I pulled the codes and received a PO0171 Lean Bank 1 and PO0174 Lean Bank 2 errors. The truck runs very smooth but it still has a hard time with the hot starts. I can stop and leave the truck for 10-15 minutes, return and the engine is very difficult to start, (Seems like it is Flooded). My first thoughts are PCV valve and/or MAF sensor. Has anyone experienced this problem before? Thanks for any help.

David

 

I haven't personally experienced this but from my reading it sounds like a fuel pressure problem. I would take pressure readings at the schrader valve while the engine is running, shortly after shutting it off and about 15 or 20 minutes after shutting it off.

 

Since this problem occurs only if the temperature is above 45 degrees, would the fuel pump be affected by temperature? The truck idles smooth without a hitch. Would a problem with the fuel pump or pressure be noticeable under other circumstances such as acceleration or idling?

 

There are more things involved in the fuel pressure issue than the fuel pump. The fuel pressure regulator controls the pressure and sends the excess gas back to the tank via a return line. Also fuel can leak past the injectors into the combustion chamber after you shut the engine off, this COULD be your hot start problem in warm weather. Bottom line fuel pressure tests need to be taken while running and at various times after shutting the engine off to evaluate the problem. It would be best to do this with the engine warmed up good to best replicate the problem. Keep in mind your problem could also be ignition related. Things like this never seem to be easy to solve. Good luck.

 

i have a '95 with 60,000 miles and have the same problem. very irratating because it doesn't do it all the time, but often enough. i haven't found any solution for it either. please let me know if you find out. i don't want to go through the uninformative diagnostic tests that many shops are eager to do with no results. anyways, let me know what comes about. thanks

 

I'm not familiar with the 4.9 but - what about the coil(s). Could they be affected by the heat?

Have you changed the fuel filter recently? If not, or never have, I would recommend that 15-minute task to see if that doesn't solve the issue.

When it is hard to start when hot, does the exhaust smell of excess, unburned fuel? That may give you a lead on which way to go.

Just thinking out loud. Hope it helps.

 

I haven't changed the fuel filter in quite sometime, so that could be done and is well over do. That would help the lean bank situation but the hot starts are confounding. Yes, the truck smells like it is flooded when I attempt a hot start. I just got back from driving at high elevation and performance was terrible. AT 8,500 feet I had to down shift to third to maintain 45 MPH on a two lane mountain road. So performance is terrible when the truck is under a strain. I did replace the MAF and PCV valve last week with no improvement in performance. The Check Engine light came back on after driving less than 10 minutes.

I appreciate the input and I will keep everyone posted on the progress.

 

Your first post tells it all.
The PCM is being allowed to run the engine rich, this is the real problem.
The OX2 sensors are not able to correct for the rich fuel.
The engine is most likley running at or near open loop condition.
Some of the reasons are fuel regulation, leaking injectors, air leak at intake system, ECT or any fault causing richness.
A fuel filter will not cause a rich condition nor affect the lean codes. What you don't understand is the lean codes are a reference to the PCM program tables and not the engine. It is telling you that the PCM has (leaned) the tables as far as possible trying to correct for an over rich condition.
You are risking shortened cat life if this continues.
I can't tell you exactly what it is but common sense and logic is the way to track it down.
Hot restart can be helped by flooring the throttle. This shuts down the injectors and clears the excess fuel to allow the plugs to fire. This action proves the over rich condition exists.
Good luck.

 

You were exactly right. The fuel pump was producing very little pressure. This was the cause of the poor performance at high altitude, the rough hot starts and the constant check engine light. I pulled the tank and replaced the fuel pump. The truck now runs smooth and has the normal acceleration. Thanks for the insight.