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Need help diagnosing fuel pressure problem.


Ronnie

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Last Friday I drove a total of 70 miles going to a cruise-in in another town. On the way there I had to go through an area that had a lot of stop lights close together and as luck would have it I had to stop at all of them. As I accelerated from the stop lights I noticed that a lot of the time my engine would hesitate like a carbureted engine would that had a bad spray pump.

 

Today I started trying to find what was causing the hesitation when pulling away from a stop light. I think I see the problem but I'm not sure what is causing it. I started by checking fuel pressure. The engine was stone cold when I stuck my fuel pressure tester on the fuel rail. I turned the key to run and the fuel pressure jumped to 32 psi and held steady. Lower than I think is acceptable. Next I started the engine and fuel pressure was steady at at 32 psi. Blipping the throttle or pulling the vacuum line off the fuel pressure regulator results in the needle on the gauge rapidly bouncing between 32 and 36 psi. If I apply 12 volts to the green prime connector the pressure holds steady at 32 psi with or without the engine running.

 

Now, here is the part that throws me for a loop. I decided to do a leak down test to see how long it would take for the pressure to drop. I ran the pump to make sure the pressure was at 32 psi the pump was putting out. After five minutes the pressure had increased to 40 psi. After ten minutes the pressure was at 42 psi. After 30 minutes the pressure had only dropped to 40 psi.  That proved the pump isn't loosing pressure through a bad check valve or Pulsator or a hose connection to the pump. It also proves the injectors aren't leaking. All that is good. I just don't understand the pressure increasing like it did over time. It usually drops.

 

Next with the tester connected and holding at 40 psi I removed the hose from the regulator. There was no change in the pressure. When I applied vacuum to the regulator the pressure dropped down to about 34-35 psi. When I released the vacuum the pressure jumped back to 40 psi. I didn't expect that. Keep in mind the pump wasn't running. I had the battery disconnected to make sure it couldn't run during any of the leak down test.

 

I see at least three things that could cause this. A bad fuel pump, a bad regulator or a clogged fuel filter.

 

What do you think my problem is? Any and all thoughts are welcomed.

 

Engine running

SAM_4337.JPG

 

Pump off for 30 minutes

SAM_4340.JPG

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I have seen a short term pressure rise like that after shutdown with a warm engine. If everything is sealed up, expansion from heat causes that. I would verify those results with another gauge but the unit illustrated is a quality brand. 32psi is awfully low if actual, especially if it doesn't snap right up with throttle input. Usually a bad regulator goes high rather than low. The behavior described is pretty much normal but it sounds very slow to respond, making my first guess a fuel filter. A system operating as it should have almost instant response. It's possible the pump is weak but I would start with the filter.

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I was thinking fuel filter too but I didn't want to sway anyone's opinion.

 

I just discovered that with the engine off I get 32 psi when I turn the key to run without starting. If I connect a jumper to the green prime connector and touch it to the battery and hold it, it causes the needle on the gauge to start quivering. If I start just touching the battery and release repeatedly, each time I touch the jumper to the battery the pressure will jump higher, eventually reaching about 42 psi and it will hold there.  What do you make of that? Does that point to a clogged filter?

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That is very peculiar indeed. So each stab at engaging the fuel pump causes a momentary surge which it holds? I am still guessing the filter for two reasons, it would act as flow reducer slowing pressure rise and second, it it relatively easy as a first step. The regulator doesn't usually act in that odd manner and is a very simple device. Just a spring calibrated at the base fuel pressure which should be 3bar or 43.5psi at sea level. A diaphragm that works with manifold vacuum to pull back against the spring reducing the gauge pressure to keep a constant pressure drop across the tip of the fuel injector.

 

I know I always have another story but this just came up yesterday. My #1 son and I have been working on our neglected 1938 Allis Chalmers WC tractor. Tune up and needed maintenance work and it fired right up, sounding really good. Will idle down to 400 rpm. As soon as we decided to try moving it it would buck and eventually quit. Looking at various items, such as point gap  and spark quality, it would fire right up again and sound cured. Long story short, the shutoff valve at the fuel tank was plugged almost solid even though the sediment bowl was full. It was so bad I was surprised it ran at all but the short intermissions would allow enough fuel to enter the carb and start and run normally for a short time. 

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I'm hoping my problem is being caused by the fuel filter. I checked my records and they show the filter was changed in 2009, two years after I got the car. I'm not sure that is correct since I have a new Purolator f33144 filter hanging from the back of my work bench that fits a Reatta. It's been hanging there so long I don't remember buying it. Maybe I forgot to put it on the Reatta but went ahead and updating my records thinking I would do it the next day or something. I hope my problem is that simple.

 

A few minutes ago I connected the jumper to the battery to get the pump running and then listened to different parts of the fuel rail and lines to see if I could here any sounds of gas returning to the tank. I heard nothing with the pressure at 42 psi. Should I be able to hear gas being returned by the regulator?

 

I don't envy you working on the tractor. I've not looked a points in several years. 🙂

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17 minutes ago, 2seater said:

That is very peculiar indeed. So each stab at engaging the fuel pump causes a momentary surge which it holds?

Yes that is correct. About three or four touches to the battery brings the pressure up from 32 to 42 psi and it will stay there for at least 15-20 minutes. Odd isn't it?

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I don't know if the fuel can be heard returning or not. Never tried that. One sure way is to crack the return fitting on the pressure regulator. If it leaks fuel below 40+psi on the gauge, then the regulator is suspect but I doubt that will happen. Remember the saving the Reatta story with bad fuel pump? It would sit and idle with the return line disconnected because it couldn't generate enough pressure to open the regulator.

 

Yah, points, what are those🙄 I still have my old kit built engine analyzer that works but I forget what the numbers mean😂

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Fuel filter changed but the plot thickens. Now pressure comes up to 26 psi when I turn the key on but the engine starts right up and runs good. Cut the key off and start touching the battery with the jumper to the prime connector will bring pressure up to about 33 psi. Now I'm wondering about the tester even though it isn't too old. Well maybe two or three years old and it's lived it's life in the trunk of my Reatta. I don't think the fuel pump got worse while I was under the car changing the filter. 🙂 Going to the parts store to get a loaner and see what it says.

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The trip to AutoZone didn't go as planned. Even though I called ahead of time to verify they had one, when I got there they told me it was already loaned out. They told me they will have one for me tomorrow morning and will call when it comes in. We'll see...

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Unlikely to start well at 26psi, or start at all. Something very odd is going on and definitely verify that gauge. Could just switch out the gauge itself with something from the hardware store 

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I'm embarrassed to say so but I don't think I had ever changed the fuel filter. I relied on my maintenance records but I think they were wrong. I didn't remember the exact procedure when I got under there. When I got it off it was filthy inside and out as if it had never been changed.

 

This gauge thing is weird.  It is a decent brand, OTC, and not very old but it doesn't seem to read correctly and now the pressure relief valve on the side has stopped working. Maybe all the heat from carrying it a couple of years in the trunk has screwed it up?

 

Maybe I will kill two birds with one stone with this little adventure. Maybe I will find the clogged filter was causing the hesitation and I will find that my fuel pressure tester is bad. I'd rather find out it is bad in the garage than on the side of the road when I really need i t. I'm not going to attempt to drive the car until I get an accurate gauge and test the pressure. Should know more tomorrow morning sometime.

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I bought my Snap On tester [the same tool # Kendall has] for cheap on e bay...

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I hope my tester is bad and not the fuel pump. I thought I was getting a good tester when I bought the OTC brand but now I'm having my doubts. Maybe I'll get a Snap On next time if it's bad. You get what you pay for.

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Fingers crossed on the fuel pump. I have a Kent Moore gauge from eBay. The gauge itself could be replaced individually if that is all that is wrong but maybe something else has happened of the drain has gone awry? 

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I have a couple of OTC 2000s, work just fine. Can check with a known air pressure.

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2 hours ago, Padgett said:

I have a couple of OTC 2000s, work just fine. Can check with a known air pressure.

Thanks. I appreciate the offer but no need to do that. I got a brand new, $190 loaner from AutoZone and their tester measures with 2 psi of mine.

 

I disconnected the return line from the regulator and no gas came out so the regulator is doing it's job. i guess the pump just isn't capable of putting out sufficient pressure. I think that explains the hesitation on acceleration since the regulator can't raise the pressure when vacuum drops.

 

When removing the gauges I noticed the gas seems have air in it. I imagine changing the filter is the reason for that. I'm going to check again after driving around the neighborhood for a while to see if the air goes away and see how the engine reacts. I guess my Reatta driving in the mountains will be on hold until cool weather gets here. I'm not going to work on it as hot as it is right now. That is a job for cool weather.

 

When I turn the key the pressure jumps up to about 26 psi. If I touch the jumper to the battery a few times it will jump up to about 32 and stay there even if I start the engine.  Before changing the filter it would go up to about 32 psi when I turned on the key, and touching the jumper to the battery would get it up to 40 psi. I don't understand that. Maybe I'm watching a fuel pump die right before my eyes.

 

One good thing is the pump will still run. That will allow me to remove the schrader valve on the fuel rail and pump the gas out of the tank before removing it to change out the pump.

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Ok, I pulled out of the driveway and when I hit the gas the engine bucked and hesitated for a minute or so and then smoothed out. I think the bucking was caused by air that got into the fuel rail when I changed the filter.

 

I drove it up and down the street behind my house several times and it ran just fine. So I threw caution to the wind and hit the highway. First I drove it several miles down the four lane highway (max speed 50) to get the engine completely warm and everything was normal. Then I turned around and drove through town where we have a total of 8 stop lights. I timed it so I stopped at all of them. Turned around again and drove home stopping at all the lights again. No hesitation at all when pulling away from the lights. Everything seemed normal.

 

When I got home I tested the fuel pressure again. Now everything is back to the way it was when I did the first test at the beginning of this thread, I have 32 psi when I turn the key to run and it stays at 32 psi once the engine is running. The relief valve on the tester now works as it should to. I didn't mention it before but the relief valve on the new AutoZone tester didn't work either. I just thought it was a fluke but apparently the relief valves on fuel pressure testers don't see air psi the same way they do gasoline psi and for some reason won't relieve the pressure.

 

Now I have to decide if I want to continue driving the car around with 32 psi fuel pressure and take a chance of the pump leaving me stranded or park the car until cold weather and replace the pump. What would you guys do???

 

Sorry about making such long posts but when my fingers get to going they don't want to stop. 🤣🤣

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You know me... I drive mine every day. Drive it till it breaks!

 But then I read 2seaters post and cooler heads prevail.

Edited by DAVES89
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I am surprised it starts without issue because that is about the maximum the red car would do and it usually took ether to give it a nudge. The big difference with the red car was the pressure bled off very quickly so most of the prime shot was gone before the engine turned over and the injectors began operation. That fuel pressure just isn't enough for spirited driving. It may pull you around okay at moderate speeds and acceleration, much like the red car, but it gradually got worse especially as the fuel and pump heated up. If it were mine, I would be thankful it didn't strand you, and bite the bullet to change the pump, or better yet, have it done so you can enjoy the summer😎  My choice would be a new turbine style pump.

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1 hour ago, 2seater said:

I am surprised it starts without issue because that is about the maximum the red car would do and it usually took ether to give it a nudge. The big difference with the red car was the pressure bled off very quickly

No problem with pressure bleeding off. My pressure goes up to 40 psi within 5 minutes of shutting off the engine and stays there for about 30 minutes. I think heat soak and fuel expansion is the reason but it does prove the pump is capable of holding pressure. It just can't build enough to begin with. 🙂

 

Like Dave, I have a hard time fixing things that are working but on the other hand I like to fix something that I know can leave me stranded. I don't want to fix it in hot weather myself and the mechanic I would trust it with likes you to bring the car with him for a couple of days ahead of time until he can get to it. Even though he has a chain link fence around his business with a locked gate, I still don't like leaving my Reatta outside at someone else''s place in the middle of town for a few days. Maybe I will talk to him and see if he can give me just in time service where he can give me a call and take it to him and get it right in the garage. He stays covered up with work and bush so he might not want to do that.

 

Other option is to stay within my 50 mile Free towing radius my insurance provides and drive it with my fingers crossed until cool weather. I'm going to think about it. Fall of the year is my favorite time for driving my Reatta. Maybe it will get cool early this year so I can fix it myself and still enjoy the Fall driving season.

 

Oh the joy of owning a 30 year old car. I guess I'm lucky that I've not had more problems than I have.

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