Should I replace the fuel pressure regulator?
04-17-10, 05:41 PM
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Should I replace the fuel pressure regulator?
Idle fuel pressure shows 34 PSI (FSM says should be about 29 PSI), and with fuel pressure regulator solenoid vacuum disconnected it's close to 40 PSI (once again, FSM says should be about 37 PSI).
In addition, the outlet pressure is about 80 PSI (FSM says should be 71 PSI).
So maybe fuel pressure regulator is ok, and just overall fuel pressure is too much? Or is this a sign of a bad fuel pressure regulator?
In addition, the outlet pressure is about 80 PSI (FSM says should be 71 PSI).
So maybe fuel pressure regulator is ok, and just overall fuel pressure is too much? Or is this a sign of a bad fuel pressure regulator?
04-17-10, 05:50 PM
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fuel pressure is close enough, if anything the pump pressure is a little high.
what are you trying to fix?
what are you trying to fix?
04-17-10, 06:04 PM
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Trying to fix this:
https://www.rx7club.com/1st-generation-specific-1979-1985-18/new-tps-now-idles-below-300-rpm-897484/
What would cause pump pressure to be high?
https://www.rx7club.com/1st-generation-specific-1979-1985-18/new-tps-now-idles-below-300-rpm-897484/
What would cause pump pressure to be high?
04-18-10, 04:58 PM
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Ok, I pulled the pump, and it's Airtex 8000, rated at 95 PSI, soooo....it should be ok, right? That's an OEM replacement. Could it be getting too much voltage and pushing too much PSI as a result?
I think I'll get a new FPR anyway, just to see if makes any difference at all.
I think I'll get a new FPR anyway, just to see if makes any difference at all.
04-19-10, 01:03 AM
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Ok, I pulled the pump, and it's Airtex 8000, rated at 95 PSI, soooo....it should be ok, right? That's an OEM replacement. Could it be getting too much voltage and pushing too much PSI as a result?
I think I'll get a new FPR anyway, just to see if makes any difference at all.
I think I'll get a new FPR anyway, just to see if makes any difference at all.
if the idle is low, and you can't bring it up with the idle speed screw on top of the TB or the idle mixture. check the timing, and start looking for a vacuum leak.
you shouldn't have to touch the throttle stop screw unless you changed something else, like you removed the BAC system or get rid of the air pump or something.
04-19-10, 10:02 AM
#6
Don't worry about the regulator. Since it is reading a bit high, it is probably one of theses reasons:
- return line to tank partially clogged
- regulator sticking a bit (probably not)
- someone installed a TII regulator
At any rate, the pressure difference that you are seeing is insignificant to how much fuel is supplied. At idle, you are looking at: sqrt(34/29) = 1.083. This means that you are using 8.3% more fuel at idle assuming everything else is the same.
For the high pressure at idle, it could be due to low engine vacuum (timing, low compression, vac leak, etc.)
How it all works is there is a diaphram with a spring with a vacuum line connected to the back side of the diaphram that leads to the orange solenoid. With the vac line disconnected, it should take 37psi to push the diaphram open enough to relief the flow back down the return line. If this return line is partially blocked or it the pump output was too much for a stock setup, then this pressure would raise higher. When the vacuum line is connected, the orange solenoid routes this line to manifold vacuum. This reduces pressure on the backside of the regulator causing it to open at a lower pressure. The difference between the readings is equal to your manifold vacuum. For stock, it is an 8 psi difference. This is about 16.3" of vacuum. In your case, the difference is only 5-6psi, so your manifold vacuum isn't as good (check timing, vac leaks, etc.).
The regulator references manifold pressure in order to maintain a contant dP across the injectors.
- return line to tank partially clogged
- regulator sticking a bit (probably not)
- someone installed a TII regulator
At any rate, the pressure difference that you are seeing is insignificant to how much fuel is supplied. At idle, you are looking at: sqrt(34/29) = 1.083. This means that you are using 8.3% more fuel at idle assuming everything else is the same.
For the high pressure at idle, it could be due to low engine vacuum (timing, low compression, vac leak, etc.)
How it all works is there is a diaphram with a spring with a vacuum line connected to the back side of the diaphram that leads to the orange solenoid. With the vac line disconnected, it should take 37psi to push the diaphram open enough to relief the flow back down the return line. If this return line is partially blocked or it the pump output was too much for a stock setup, then this pressure would raise higher. When the vacuum line is connected, the orange solenoid routes this line to manifold vacuum. This reduces pressure on the backside of the regulator causing it to open at a lower pressure. The difference between the readings is equal to your manifold vacuum. For stock, it is an 8 psi difference. This is about 16.3" of vacuum. In your case, the difference is only 5-6psi, so your manifold vacuum isn't as good (check timing, vac leaks, etc.).
The regulator references manifold pressure in order to maintain a contant dP across the injectors.
04-19-10, 01:36 PM
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Don't worry about the regulator. Since it is reading a bit high, it is probably one of theses reasons:
- return line to tank partially clogged
- regulator sticking a bit (probably not)
- someone installed a TII regulator
At any rate, the pressure difference that you are seeing is insignificant to how much fuel is supplied. At idle, you are looking at: sqrt(34/29) = 1.083. This means that you are using 8.3% more fuel at idle assuming everything else is the same.
For the high pressure at idle, it could be due to low engine vacuum (timing, low compression, vac leak, etc.)
How it all works is there is a diaphram with a spring with a vacuum line connected to the back side of the diaphram that leads to the orange solenoid. With the vac line disconnected, it should take 37psi to push the diaphram open enough to relief the flow back down the return line. If this return line is partially blocked or it the pump output was too much for a stock setup, then this pressure would raise higher. When the vacuum line is connected, the orange solenoid routes this line to manifold vacuum. This reduces pressure on the backside of the regulator causing it to open at a lower pressure. The difference between the readings is equal to your manifold vacuum. For stock, it is an 8 psi difference. This is about 16.3" of vacuum. In your case, the difference is only 5-6psi, so your manifold vacuum isn't as good (check timing, vac leaks, etc.).
The regulator references manifold pressure in order to maintain a contant dP across the injectors.
- return line to tank partially clogged
- regulator sticking a bit (probably not)
- someone installed a TII regulator
At any rate, the pressure difference that you are seeing is insignificant to how much fuel is supplied. At idle, you are looking at: sqrt(34/29) = 1.083. This means that you are using 8.3% more fuel at idle assuming everything else is the same.
For the high pressure at idle, it could be due to low engine vacuum (timing, low compression, vac leak, etc.)
How it all works is there is a diaphram with a spring with a vacuum line connected to the back side of the diaphram that leads to the orange solenoid. With the vac line disconnected, it should take 37psi to push the diaphram open enough to relief the flow back down the return line. If this return line is partially blocked or it the pump output was too much for a stock setup, then this pressure would raise higher. When the vacuum line is connected, the orange solenoid routes this line to manifold vacuum. This reduces pressure on the backside of the regulator causing it to open at a lower pressure. The difference between the readings is equal to your manifold vacuum. For stock, it is an 8 psi difference. This is about 16.3" of vacuum. In your case, the difference is only 5-6psi, so your manifold vacuum isn't as good (check timing, vac leaks, etc.).
The regulator references manifold pressure in order to maintain a contant dP across the injectors.
his pump outlet pressure, is 10psi over what the FSM says it should be, pressure at the rail is 2-3 psi over what it should be, regulator/ return line etc works...
oh and look up the part numbers, t2 gsl-se and 12a turbo all use the same FPR
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04-19-10, 04:38 PM
#8
I read his post. 
1. The dead headed pump pressure doesn't mean a thing. As long as it is over the regulation pressure point + line losses, it doesn't matter what the pressure is. The 80 psi is fine. It would also be fine if it was 120 psi. The regulated pressure at the rail should still be the same regardless. The only difference is if you went to a larger pump (volume). Increased flow = increased resistance = higher pressure shown at the rail.
2. His idle fuel pressure is 5 psi high. This is assuming that his gauge is accurate. With the line disconnected, he is about 3 psi high. The fact that the spread in the reading is less than stock, indicates that the manifold vacuum is weaker than it should be (timing, vac leak, low compression, etc.).
3. For reading high in both cases (line off and line on):
- the tolerances in the regulator causes the setpoint to be higher than what the FSM shows
- his gauge is inaccurate
- there is additional resistance compared to stock on the return line (2-3 psi higher)
4. True, I did not bother to check the part # on the regulator. However, the TII FSM does give a range of ~34 - ~39 psi (instead of the fixed 37 psi).
I am saying that his readings are not the cause of his problems. It is more the other way around. If he gets the thing to idle better, the fuel pressure at idle will drop closer to what the FSM states. It will still be about 2-3 psi (instead of 5) high as the "line-off" reading is also 2-3 psi high.
I've seen cases where the regulator failed shut and the rail was seeing 65 psi. Car ran okay, just ran rich. Double the pressure gives about 41% more flow.
1. The dead headed pump pressure doesn't mean a thing. As long as it is over the regulation pressure point + line losses, it doesn't matter what the pressure is. The 80 psi is fine. It would also be fine if it was 120 psi. The regulated pressure at the rail should still be the same regardless. The only difference is if you went to a larger pump (volume). Increased flow = increased resistance = higher pressure shown at the rail.
2. His idle fuel pressure is 5 psi high. This is assuming that his gauge is accurate. With the line disconnected, he is about 3 psi high. The fact that the spread in the reading is less than stock, indicates that the manifold vacuum is weaker than it should be (timing, vac leak, low compression, etc.).
3. For reading high in both cases (line off and line on):
- the tolerances in the regulator causes the setpoint to be higher than what the FSM shows
- his gauge is inaccurate
- there is additional resistance compared to stock on the return line (2-3 psi higher)
4. True, I did not bother to check the part # on the regulator. However, the TII FSM does give a range of ~34 - ~39 psi (instead of the fixed 37 psi).
I am saying that his readings are not the cause of his problems. It is more the other way around. If he gets the thing to idle better, the fuel pressure at idle will drop closer to what the FSM states. It will still be about 2-3 psi (instead of 5) high as the "line-off" reading is also 2-3 psi high.
I've seen cases where the regulator failed shut and the rail was seeing 65 psi. Car ran okay, just ran rich. Double the pressure gives about 41% more flow.
04-19-10, 05:20 PM
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and that's a good point about the intake vacuum.
having worked on these forever, if the spec is 34-39 with the hose connected and 45 without, and my gauge says 41 and then 49, its close enough, the pressure is changing like its supposed too, the extra 2psi could be gauge error, or a bunch of other things.
we actually tried that at the shop one time, we compression tested the same engine with 3 different compression testers, and it was all over the map. this was 10+ years ago, so i don't remember exact numbers, but the spread was bigger than the FSM limits for a good engine vs a bad one.
04-20-10, 07:36 AM
#10
Exactly. We don't know for certain where the difference is coming from, so that is why I tried to list the possibilities. The more important number is the difference in the readings between the line connected and it not connected. By using the same testing equipment, you are eliminating the error in the gauge reading and you are finding a poor manifold vacuum in this case (could be verified with a vacuum tester). Usually a given pressure gauge may read incorrectly, but read the same amount incorrectly every time with a given pressure. It comes down to accurate vs. precise.
Say input pressure is 37psi. If the gauge is accurate, but not precise, you may get readings like this:
36.5 psi, 37.5 psi, 37 psi
Now if the gauge is precise, but not accurate, the readings may be:
41.0 psi, 41.0 psi, 41.0 psi
It really comes down to the quality of the gauge and the calibration of it. If the gauge is liquid-filled, then the temperature difference of the gauge when taking a reading and the temperature at the factory when it was assembled willl also throw off the reading. People run into this problem when they mount a fuel pressure gauge in the engine bay. When the thing heats up to 120-140F, the reading is way off since the gauge was probably assembled at ~68F.
It boils down to we don't know the exact reason why the line off reading is a couple psi high. There are several possibilities that would cause it. The reason could be determined with more extensive testing, but really it does not matter. Partially, it is due to the fact that the flow goes as a squareroot of the pressure (you need 4x the pressure to get 2x the flow through the injectors).
On those compression tests, I assume you compensated for any changes in cranking speed. I'm not surprised by the spread you found. These things get calibrated at the factory when they are made, and probably are never calibrated again. You can imagine that being used in a shop for 15-20 years with the sensor being dropped, banged around, and just being used could cause the calibration to be lost. The FSM assumes you are using a new/calibrated tester with the numbers it reports.
Say input pressure is 37psi. If the gauge is accurate, but not precise, you may get readings like this:
36.5 psi, 37.5 psi, 37 psi
Now if the gauge is precise, but not accurate, the readings may be:
41.0 psi, 41.0 psi, 41.0 psi
It really comes down to the quality of the gauge and the calibration of it. If the gauge is liquid-filled, then the temperature difference of the gauge when taking a reading and the temperature at the factory when it was assembled willl also throw off the reading. People run into this problem when they mount a fuel pressure gauge in the engine bay. When the thing heats up to 120-140F, the reading is way off since the gauge was probably assembled at ~68F.
It boils down to we don't know the exact reason why the line off reading is a couple psi high. There are several possibilities that would cause it. The reason could be determined with more extensive testing, but really it does not matter. Partially, it is due to the fact that the flow goes as a squareroot of the pressure (you need 4x the pressure to get 2x the flow through the injectors).
On those compression tests, I assume you compensated for any changes in cranking speed. I'm not surprised by the spread you found. These things get calibrated at the factory when they are made, and probably are never calibrated again. You can imagine that being used in a shop for 15-20 years with the sensor being dropped, banged around, and just being used could cause the calibration to be lost. The FSM assumes you are using a new/calibrated tester with the numbers it reports.
10-14-10, 10:26 AM
#11
I am having the same issue. Has same fuel specs as his and runs rough on idle and low rpms. It runs rich. backfires upon decal, also backfires then the rpm stalls(stay at same rpm even if you push down accelerator) then when you let off the throttle rpm drops then car dies. then i have trouble starting it back up. sometimes i can get it to start by pulling the efi fuse. cranking it over then replacing and starting car. but alot of the time not. so im pretty sure its getting flooded. now i havent tested the manifold vaccum. how would i go about that and what pressures should it be at? i have replaced the fuel pressure reg and have pressurized the return line with air to check. this has been troubling me for months now. i need to get it fixed. i have a new car i need to get this one fixed so i can get it smogged and sold. i love rx7s but im a college kid with no time or money. please any help is appriciated. thanks
10-14-10, 11:39 AM
#12
Waffles - hmmm good
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It really comes down to the quality of the gauge and the calibration of it. If the gauge is liquid-filled, then the temperature difference of the gauge when taking a reading and the temperature at the factory when it was assembled willl also throw off the reading. People run into this problem when they mount a fuel pressure gauge in the engine bay. When the thing heats up to 120-140F, the reading is way off since the gauge was probably assembled at ~68F.
almost zero after running for a bit. Its a liquid filled Summit brand. Seems to be
fairly accurate cold but once its hot you can't trust it. Doesn't help that its mounted
almost over the header either
Thanks Kent for that gem and now back to your regularly scheduled progarmming ...
10-14-10, 05:55 PM
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I am having the same issue. Has same fuel specs as his and runs rough on idle and low rpms. It runs rich. backfires upon decal, also backfires then the rpm stalls(stay at same rpm even if you push down accelerator) then when you let off the throttle rpm drops then car dies. then i have trouble starting it back up. sometimes i can get it to start by pulling the efi fuse. cranking it over then replacing and starting car. but alot of the time not. so im pretty sure its getting flooded. now i havent tested the manifold vaccum. how would i go about that and what pressures should it be at? i have replaced the fuel pressure reg and have pressurized the return line with air to check. this has been troubling me for months now. i need to get it fixed. i have a new car i need to get this one fixed so i can get it smogged and sold. i love rx7s but im a college kid with no time or money. please any help is appriciated. thanks
Manifold vacuum is easy to check if you have a vacuum pump with a gauge. I usually tap into any of the vacuum lines (mind you not all lines have manifold vacuum in them) with a T-connector. I use either vac switch line or one that goes to the BAC. Just start the car and look at what the gauge reads. Should be around 17 - 18 inches of mercury at idle, if all is well. Last I checked my read something like 15-16, but it's a cheapo gauge, so I don't know how accurate it is, and I was still early in the engine break-in.
10-15-10, 10:09 AM
#14
I got a new FPR a while ago and my readings were still the same, which means it's probably not a fuel pressure issue, but engine vacuum etc.
Manifold vacuum is easy to check if you have a vacuum pump with a gauge. I usually tap into any of the vacuum lines (mind you not all lines have manifold vacuum in them) with a T-connector. I use either vac switch line or one that goes to the BAC. Just start the car and look at what the gauge reads. Should be around 17 - 18 inches of mercury at idle, if all is well. Last I checked my read something like 15-16, but it's a cheapo gauge, so I don't know how accurate it is, and I was still early in the engine break-in.
Manifold vacuum is easy to check if you have a vacuum pump with a gauge. I usually tap into any of the vacuum lines (mind you not all lines have manifold vacuum in them) with a T-connector. I use either vac switch line or one that goes to the BAC. Just start the car and look at what the gauge reads. Should be around 17 - 18 inches of mercury at idle, if all is well. Last I checked my read something like 15-16, but it's a cheapo gauge, so I don't know how accurate it is, and I was still early in the engine break-in.
10-17-10, 01:40 AM
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No flooding.
I've fixed a lot of issues, each one made slight improvements. Car runs pretty well now. Idles at around 900 or so. Still a bit of a roughness here and there, but it seems to be getting better as I break it in. Considering how old the tech is, I'd say all the systems are probably working as well as they can.
You can work the seals through the exhaust ports to get them unstuck and to just generally inspect them.
Does it turn over and feel like it's trying to fire? It's probably just flooded. Do a de-flood procedure - the complete one. Pull the spark plugs, clean and dry them, etc. If that doesn't work, try a pull start. If you get it running at all, warm it up and check compression, timing, and manifold vacuum.
I've fixed a lot of issues, each one made slight improvements. Car runs pretty well now. Idles at around 900 or so. Still a bit of a roughness here and there, but it seems to be getting better as I break it in. Considering how old the tech is, I'd say all the systems are probably working as well as they can.
You can work the seals through the exhaust ports to get them unstuck and to just generally inspect them.
Does it turn over and feel like it's trying to fire? It's probably just flooded. Do a de-flood procedure - the complete one. Pull the spark plugs, clean and dry them, etc. If that doesn't work, try a pull start. If you get it running at all, warm it up and check compression, timing, and manifold vacuum.
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