My car has been acting up after it worms up and it has been getting very poor fuel economy, about 10 - 11 mpg in the city. It also has been hard to start when hot. It will start and die immediately if I try to start it when hot. I have to give it a little bit of gas to start it, and then its fine after that. It also has intermittent performance problems when hot. Sometimes it will run like a raped ape, and sometimes it will sort of not respond as well, almost as if it is too lean. Also, when I drive it at very low speeds in a parking lot in first or second gear, and decide to give it a little bit of gas, It will get very jerky.
I have no stored codes, and the SES light is not on. I fear that something is failing, but has not gotten bad enough to where it is throwing trouble codes. I have checked the fuel injectors, and they are all between 14.7 and 15 ohms.
The engine was freshly rebuild from the oil pan up 4000 miles ago. It has a comp cam cam shaft with the following specs: 206 int / 212 ex. @ 0.050.
0.480 int / 0.488 ex. with 112* LSA.
The car seems to run very strong and starts well when cold.
I will check the fuel pressure this weekend, although I hear the pump engage when I turn on the key. I have removed the vacuum line from the stock FPR to see if there are any fuel leaks, and there are non.
Base timing was set to stock specs @ 6* BTD.
The car has new catalytic converters, spark plugs, wires, distributor cap, rotor, new fuel filter, and new coolant temp sensor.
Any help and suggestions would be greatly appreciated. I want to take the car on its first cross country trip over Labor Day weekend, and now I am reluctant to do this with the car in its present state.
Sorry for the long post and thanks in advance.

 

From my experience, no. Generally speaking when in tank fuel pumps go, they just go with no signs of lost use from the pump, Normally when a pump goes out its cuz it locks up or it has a manufacturers defect internally from the get go. id look at fuel delivery and check whats going on in the engine even though its fresh, get a AFR gauge and check out how its looking as far as that goes

Sorry i cant offer more info but id hate to steer you in a completely wrong direction

 

yeah the thing about fuel pumps is when they go, they just go. no warning or nothing. it kinda sucks because a problem out of nowhere will drive you crazy, atleast if it did give a symptom of poor fuel economy atleast then you might replace it before it goes out. but really fuel pump really just die out of nowhere

 

My experience with in-tank electric fuel pumps has been they degrade, lose power, are hard to start, and produce poor fuel economy due to a poor spray pattern from reduced pressure.

 

I just finished testing my fuel pressure at the shrader valve on the fuel rail and here are the results:
With the vacuum line disconnected from the FPR, the pressure rises quickly to 50 PSI and does not hold. It falls rapidly. No fuel come out of the FPR vacuum port. With the vacuum port connected, the fuel pressure rises quickly to over 40 PSI and also drops rapidly to 0. With the engine running and vacuum port connected to the FPR, pressure holds steady at 40 PSI. When I apply the throttle the fuel pressure rises a little bit and then it drops to about 36 - 38 PSI. If I keep the throttle applied, fuel pressure rises a little bit to just below 40 PSI.
I have no idea what to make out of this. I don't know what is causing my fuel pressure to decay so rapidly. I know it could be either bad fuel pressure regulator, leaking fuel injectors, or some valve inside the fuel pump, but don't know how to test for either one of those.

 

Also, could this rapid fuel pressure decay be causing the drivability problems that I have described in my post above, or should I be looking at other things, such as timing advance due to the new cam. Any suggestions would be greatly appreciated.

Thanks

 

I see so many posts on this website where people have 'hard to diagnose' problems, no codes at thrown, they replace lots of parts and eventually they find that the fuel pump (or associated parts) had a problem (the last part they want to replace). It is sort of a pattern I see. So I would further investigate that the fuel pump pressure fluctuation. If the pump was easy to get to and it was inexpensive I would say to replace it first THEN look for other problem sources !!

You say you have a 'hard start problem' when the engine is hot. Maybe you can get the engine hot, shut it off, then watch the fuel pressure carefully when a friend tries to start the hot engine. In other words put the engine is a condition where you KNOW you tend to have a problem and then look at the various readings such as temperature, fuel pressure, air restrictions, etc. at that point.

 

This is what I was trying to do. The car was at 220* when I took these measurements. I know that there is a problem with fuel pressure decay, however, I don't know if that was a pre-existing problem, since FP is constant for the most part while the car is running, or if there is something else that is causing my imperfections in the manner in which the car should run. I can't necessarily say that it is fuel pressure that is casing the issues I have. I was hoping that someone would be able to suggest some things that I can look for.

 

Here is a thread I found that is suspiciously similar:

http://car.justanswer.com/car/1aash-...-7-tpi-problem

I am not sure that the problem was officially solved but you can read some similarities.

They allude to a check valve within the fuel pump being bad and causing the rapid decline in fuel pressure when the engine is not running.

But when the engine is running the fuel pressure is adequate (similar to yours).

It also mentions hard starting when the car has been sitting in the sun on a hot day.

It mentions eliminating the fuel pump regulator as contributing to the rapid decline in fuel pressure if the pressure drops off quickly even though the return fuel line is BLOCKED OFF.

The fuel pressure would normally drop slowly when the engine is stopped and parked. This is because the pressurized fuel, being between the one way valve (in the fuel pump ?) and the non-firing injectors and the closed regulator should have only one place to escape, that being one or more tiny 'pressure bleed holes' that are drilled in the carburetor from the high pressure side to the fuel return line. This is to eliminate the fuel from being under high pressure for any extended period of time after the engine has been shut off.

 

Actually, the part that is of a bigger concern to me is not so much the hard starting, but the poor fuel economy and drivability problems that I am experiencing. Could these be related to the rapid FP decline when the engine is not on, because pressure seems to be steady when the engine is running.
I guess I will try to find a place this week that can diagnose the problem better than I can.

 

I think this is ALL related. My bet is that the fuel pump has a bad one way valve. The poor fuel economy could be due to the need to force MORE fuel through the injectors to make up for a poor spray pattern like five7kid suggested above. This make sense to me.

 

The only test I could think of that would tell you if the fuel injectors are 'leaking' would be to insert another one way valve into the fuel feed line such that fuel can reach the carburetor but cannot flow back into the fuel tank. Then create pressure from the fuel pump, turn off the car and see how long it takes for the fuel pressure to drop. This would completely remove the need for the fuel pump one way valve in THIS test. And if the pressure dropped FAST then at THIS point it cannot be due to the fuel pump one way valve condition. It would have to be due to something like fuel injector leaking or some type of unknown excessive fuel escape route.

 

If you found the external one way valve actually helped a lot then it might be possible to test the driving issues and hot engine start issues and find they have been eliminated. The only concern I would have is that the placement of the one way valve would determine how much VOLUME of fuel was being held pressurized by the external one way valve. Normally this volume would be the volume of fluid from the fuel pump one way valve to the injectors. If you placed an external one way valve in line near the engine (at a convenient hose connection) you will have reduced the VOLUME of fluid under pressure. The reduced VOLUME might play a part in the change in injector fuel pressure.

 

I don't know if leaking fuel injectors would cause such a rapid decline in fuel pressure. I am suspecting that it is either the check valve in the fuel pump, or the fuel pressure regulator. I don't know which of the fuel lines is the return line to the tank. They both look the same. Perhaps If I pinch the return line and see that fuel pressure holds and does not drop, it would be the fuel pressure regulator.
Does anybody know how fast usually fuel pressure bleeds down in the case of leaking fuel injectors?
Thanks