How to measure fuel pressure

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How to measure fuel pressure

Postby Andrew99 » Thu 17.09.2015, 05:00

So I've read through the forum and it appears to be easier to replace a fuel pump
than it is to measure it. I can't find a port to plug a meter into on the fuel rail.
At the fuel tank the I can't figure out how to get the hoses off to try and measure
it there.

Is there a fuel port on the rail?

how do you remove the lines from the tank?

should the rail pressure be 50 to 60 psi?

Any info on the subject would be appreciated.

Andrew
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Re: How to measure fuel pressure

Postby Brit-Car-Nut » Thu 17.09.2015, 13:10

I have seen a few attempts at adding a port to the fuel rail, but it isn't real easy. The only way to test fuel pressure is to use an adapter like the one Lotus mentions in the service manual. You need a "Tee" fitting that goes in the return line under the intake manifold and then you connect the pressure gauge to the fitting.
Fuel-pressure.jpg

Lotus put their adapter on the Aftersales list and I jumped and bought one only to find it was just like the Harbor Freight adapter without the other lines and gauge and it was twice the price.

To remove the lines at the pump, there is a tool that is shown in the service manual that puts equal pressure on the slip-lock device Lotus used. I have them listed for sale here: http://forum.lotuselancentral.com/viewt ... 56#p281812


Others have suggested making your own tool using pop-rivets (I hate having to fabricate) or just using small screwdrivers but I have had the screwdrivers slip enough times and nick my hands that I found the real tool.
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Re: How to measure fuel pressure

Postby Andrew99 » Thu 17.09.2015, 16:07

John,

Thanks for the great response!

I bought that exact kit from Harbor Frieght before I wrote my post. Then
came here when I couldn't find a way to hook it up. So do I need to
take off the intake manifold to tap into the line. Is it a rubber hose?
Do I have to splice it into the line? Did yours read 50 to 60 psi?

Thanks again for the help,

Andrew
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Re: How to measure fuel pressure

Postby Brit-Car-Nut » Thu 17.09.2015, 16:44

Andrew: you need to find the return line under the intake manifold and using the short pieces of fuel line and the hose clamps, put the "Tee" adapter in-line where it connects to the solid line (crowded but doable).

Fuel Line2.jpg


You are looking for the 5/16" or 3/8" plastic/nylon line (I don't remember which) that connects to a steel line with a piece of fabric hose, not the one that has the brass fitting on the end.

I never used the tool because it took 6 weeks to get here. Since my pump didn't work at all, I replaced it (I used a generic pump EP-240 - $14.00 on eBay #400205704860) and also replaced the Fuel Pressure Regulator (Standard Motor Parts PR92T) and my car started up right away. There are lots of pumps available that interchange with the EP-240 designation. None are exact replacements, but it is mainly the electrical connection that needs to be modified.

The only difference between the PR92 and the PR92T is the PR92T doesn't come in a RETAIL package. and it is clear zinc plated compared to yellow zinc plated
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Re: How to measure fuel pressure

Postby Ian T » Thu 17.09.2015, 19:37

Hi John, Are you sure that the pressure measurement should be made in the return line?

I ask as that is after the fuel pressure regulator and you'd be measuring the resistance to flow back to the tank. When I did it, I fitted it inline with the flow pipe, which meant that it saw the pressure against the reguator.

Regards,

Ian.


EDIT: Here's a link to my project thread, which shows what I did. As John says, you can get to the pipes while they are still behind the inlet plenum, but it's congested and fiddly. You have to get at them to remove the rail as I did, but that was for other reasons (i.e. I wanted to look at the injectors). viewtopic.php?f=79&t=23531
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Re: How to measure fuel pressure

Postby Brit-Car-Nut » Thu 17.09.2015, 20:48

Ian: the service manual shows the adapter and I wouldn't believe they would want to have us cut the nylon feed line so I assumed they wanted it to go in the return. I agree it didn't make much sense. Page 10 of EMK3 shows a fuel pressure gauge being added to the feed line using a completely different apparatus from what Lotus sold as the adapter. I believe the kit I suggested has the correct fittings to actually make up the test fitting, but I will need to test it as soon as I can dig out the necessary parts. I will also look into finding the correct fittings so others can make a test port using standard available parts.

Fuel Pressure Rig.pdf

Sorry for assuming something that Lotus doesn't really explain or describe.
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Re: How to measure fuel pressure

Postby Ian T » Thu 17.09.2015, 22:00

Yes, I agree that Lotus wouldn't suggest we cut the high pressure pipe. :)

Here's the kit I borrowed:
Image

Essentially the tee fitting is a threaded item on this one and so are the hoses - I had to select by trial and error, a pair of adapters from the kit to fit onto the ends of the hoses to make the connections to my fuel pipes, but once fitted there were no leaks.

The diagram does show it on the feed, but as was common with that age of drawing, we can't make out the threaded fittings on the pipes very clearly. I believe the diagram points to the feed, not least because I can't see how to measure the rail pressure after the exhaust from the FPR.

On that basis, I believe (but can't say I'm sure) you may need a couple of additional adapters with that Harbor Freight kit to convert the plain hose back to a threaded fitting to mate up the two ports of the tee with the male and female parts of the (Lotus) fuel feed hose.

If I hadn't managed to borrow one, I think I would have bought something like this set: http://www.ebay.co.uk/itm/Fuel-Injectio ... 43e1bb9da9

Or, a cheaper, permanent option would be to cut the feed pipe and fit something like this: http://www.ebay.co.uk/itm/Fuel-Pressure ... 51c38905e9 which would be the way to use the HF kit assuming you don't mind cutting and re-terminating the pipe.

Hopefully this helps. :)

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Re: How to measure fuel pressure

Postby Andrew99 » Thu 17.09.2015, 22:34

I'm going to see if I can make the harbor freight tool work and I'll let you guys know what happens.

Thanks for all the great information,

Andrew
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Re: How to measure fuel pressure

Postby Andrew99 » Sat 19.09.2015, 18:10

My first attempt at reading the fuel pressure has failed. Hooking the gauge behind the plenum looks impossible
without the proper fittings. So I hooked it up at the tank. The line with the red connector reads nothing on
my gauge (probably vacuum). When I hook it up to the other line it squirts fuel out of the T fitting from the
Harbor Freight kit. The kit is (bad from stock) threads missing from inside of T. I guess you get what you pay
for. It took a lot of hoses and fitting from my garage to get it to even hook up, just to have the kit be defective.
So I'm going to take it back to the store and hopefully I can trade up to a kit with more fittings. if not I can make
the same kit work if its not broken and I get some more hose clamps.

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Re: How to measure fuel pressure

Postby Brit-Car-Nut » Sat 19.09.2015, 22:19

The tank line with the RED ring is the fuel return so it will not have any measurable pressure.

Since I was taking pictures of my new engine for some CAS questions, I installed a fuel rail and lines to show what it looks like from the back-side of the engine.

The fuel lines are 14mm 1.50 pitch. GM and many Japanese cars use that size, so you should be able to find appropriate fittings that will work.

Sorry, Harbor Freight has always had quality control problems and sometimes you have to try several of their sets before you find one that actually works.

You can click on any of the pictures to see a larger version.

Fuel-Line1.jpg


Fuel-Line2.jpg


Fuel-Line3.jpg
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Re: How to measure fuel pressure

Postby Andrew99 » Mon 21.09.2015, 20:43

So I exchanged the harbor freight fuel pressure test kit for another. I was going to get the better kit but it was $90 this one is $20. The new
kit is no better. From reading the manual it is clear that the kits T fittings threads will not match up to the connectors given. I just epoxied
the meter to the T to get it to work. I won't be able to use it for other cars but at $20 it works for this one.

The reading at the black labeled hose from the tank reads 40 psi with ignition on and about the same started and revving. Seems stable

Is this enough? Could this be the cause of my poor performance.

2 years ago I replaced everything else (for a different issue)

new O2 sensor
new spark plug wires
checked spark plugs for gap and consistent color
new thermostat
cleaned throttle body and Seafoamed intake
ran a half tank of gas with a bottle of Seafoam in it
checked system for vacuum leaks
Checked PVC valve
Changed oil and washed K & N air filter
adjusted base timing
Checked ERG valve
swapped the alternator
Fuel pressure regulator
New coil packs
Re-soldered the Hall Effect (the Charlie way).
Removed injectors and had local shop test and clean them
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Re: How to measure fuel pressure

Postby Brit-Car-Nut » Mon 21.09.2015, 22:22

From the Engine Management Manual:

pressures.jpg
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Re: How to measure fuel pressure

Postby Andrew99 » Wed 23.09.2015, 17:10

So the fuel pressure is good at 40 psi. When I pull each spark plug #3 has no change and the spark seems strong out of the cable. Swapped the spark plugs 1 and 3 no change. This leaves the injector. I had the injectors reconditioned at a local shop a few years ago (50 miles ago) but I guess when they're 24 years old they can go at anytime. I might try and swap the injectors around to see if I can move the problem to another cylinder just in case it's a cable issue or just put in a new set of RC engineering's PL2‑0320.

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Re: How to measure fuel pressure

Postby Ian T » Wed 23.09.2015, 19:27

Hi Andrew,

I think you are on the right lines.

Have you done a compression test on the engine? As a nice simple test, it gives you some confidence that if fuel and spark are there, you have enough squeeze to make a bang.

Moving the injector is fiddly, but a good idea. You might also check its resistance using a multimeter and compare with the others. If it is open circuit, you have a definitive diagnosis, but it could also be stuck, so the substitution method would show that nicely.
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Re: How to measure fuel pressure

Postby Andrew99 » Sat 26.09.2015, 17:20

So I found someone local selling a new set of RC 320's for $100 and set up a time to get them at the beginning of next month (he's currently out of town). While I waited I thought I'd swap
the injectors around and do a compression test just to make sure. Well.... problem did not move with the injector, compressions good at 110 and I put in a different SPARK PLUG and its running fine now. The plug was the first thing I checked weeks ago but I must have not switched them when I thought I had.

Question:

Should I buy the injectors?
Are RC 320s an upgrade?
They are so cheap should I swap them anyway?
Maybe save them for a future repair?

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Re: How to measure fuel pressure

Postby Ian T » Sun 27.09.2015, 15:05

If it's running right now, I wouldn't change anything.

I don't know about the RC injectors, but I'm sure that John will be along shortly and know the answer.

Having a spare set of brand new injectors (assuming they are stock spec) in your stock is a very well worthwhile investment. They last almost forever, but will get less easy to buy as the years pass and knowing you have some ready to go is a great insurance policy. The other way to look at it is that you can't lose money on them, as there will always be someone else willing to cover your purchase costs if you did want to part with them.

Well done for swapping out the spark plug, it's hard to bring yourself to change something again that you've already covered.

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Re: How to measure fuel pressure

Postby Brit-Car-Nut » Sun 27.09.2015, 16:19

New injectors?

A NEW RC Engineering PL2-0320 (current part number) is $88.75 (around £55.00) EACH. A SET for $100.00 is amazing and a major loss for someone.

If you know the seller and are sure they are really RC Engineering injectors and they are NEW, That is an amazing deal and a great investment. RC also offer a high resistance injector that is not compatible and much less expensive.

Just be certain you aren't being misled and make sure you test them before the guarantee expires....
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