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Figuring Hot Engine Fuel Pressure Bleed

I have a '97 Escort - 2.0L multiport injection - that doesn’t hold fuel pressure - but only when hot. With cold car and cool air temps the pressure holds just fine.

I have checked as thoroughly as I can for external leaks and have found no evidence of that. I’m assuming that this points to either pressure regulator (typical vacuum controlled) or fuel injector leakdown. I guess it could be the fuel pump check valve, but the hot engine part just makes me assume it isn’t.

I have pulled the vacuum hose from the regulator many times now and have never found any liquid gasoline - though it does smell of gasoline. The regulator also seems to function properly judging by fuel pressure while the car is running. (Pressure remains solid and within specs at idle; jumps 5-6lbs & falls back w/ throttle snap; jumps 8-9 lbs & remains steady if I pull the vacuum hose from the valve).

I’m thinking injectors, but I’d really like to know for sure before I pull the fuel rail.

I can’t pinch off hoses to tank as they are solid body hoses. I could pull the plugs and smell, but the head is aluminum and I’ve been told not to pull hot spark plugs, and it won’t work if they aren’t hot.

Is it ok to pull the plugs hot? Any other shade tree tricks for pinpointing this kind of pressure bleed?

Sorry - I should have mentioned if it wasn’t apparent that I am watching the bleed down on a fuel pressure gauge - not by any kind of guessing or car behavior.

What’s the problem you’re trying to fix? Is it losing fuel pressure while it’s running and cutting out?

As for the plugs, the real risk is if you’re changing them hot after they’ve been in there for a while, the threads on the plug basically get fused to the threads in the head and both come out with the plug! The safe thing to do if you absolutely have to pull them hot would be to take them out when the engine is cold and coat the threads with anti-seize lubricant. Put 'em back in and warm the engine up and you should be able to take them out without too much trouble. Look out, though, because spark plugs out of a hot engine are extremely hot!

I don’t think “the” problem is necessarily “a” problem (i.e. I think I have more than one issue) and it would take a book that no one wants to read. Over the summer I did have some hot restart problems on occasion - mostly with both engine and weather very hot. All I had to do is juice the throttle and things would stabilize.

At the moment, I have a bit of a rough idle - acting like a miss. I just replaced the plugs, inspected/tested wires & coil both of which have lt 10K miles on them. So I just went from spark to fuel - decided to check my fuel pressure and the bleed down came up. It actually causes no cold start problems at all, but - I think - the occasional hot start problem. If I can figure out a leaky injector or two I’ll replace them whether they have to do with the miss or not.

I think you may be on the right track with the leaky injector suspicion. Have you pulled and looked at the injectors? Are any of the plugs carboned up or otherwise anomolous?

I probably didn’t need the new plugs I just put in - the old ones had only about 10K or less and looked perfect (dry, light gray to tan - no black, no sign of fouling, all 4 looked the same).

I haven’t pulled the fuel rail yet. Pulling it is not all that hard, but it is also not all that easy, and I’ve never done it before so add 50-100% time for what it would take someone else. I’m trying to establish a good reason the pull the rail before I do. I’d also like to have new injectors on hand if I need them, so if there is some way to sort it out I’d rather save the work.

I’ve also never inspected a fuel injector. How does one inspect an injector once its been pulled?

I tried unsuccessfully to find a good visual reference guide.

Generally, if the pintle isn’t closing completely there’ll be carbon buildup from the extra gas. Generally it’ll show on the plug also. Since this is only happening when it’s hot it may not be as pronounced.

Contamination can also be a factor and this should be visually evident.

You could always buy a new one and do a visual comparison, then if you don’t find anything evident return it for refund. There are flow, operation, and pattern tests with the proper equipment, but without the setup visual is really all you can go by.

Thanks much. It is the “proper equipment” part that I’m obviously trying to avoid whether buying it (which would be nuts) or paying someone who has it.

I think - going partly on what GreasyJack had to say, I’ll loosen and just snug up the plugs with the engine cool, idle it 'til hot, pull them and sniff the cylinders. Then I’ll pull the rail if that seems to be the source. I’ll let you know how it goes.

If you can do without the car for a few days, you can send the injectors off for testing/cleaning/repair. I’ve had good luck with this place:

They’ll do your set for $68 plus shipping. The turnaround time is short.
I’m not in any way affiliated with them, I’ve just had good service.

The test procedure according to ALLDATA says to inspect the fuel system for leaks, check for fuel at the vacuum line for the pressure regulator, remove and test the injectors for leakage, if all of these test OK then replace the fuel pump module.

If there isn’t a driveablility problem or a hard start hot problem then I would assume the injectors are not leaking. This would then point to the fuel pump module leaking but the only way to confirm it is to have the injectors tested.

So the last time I drove home I let the car cool for a little while and then pulled the plugs (I had just put them in last weekend, had used anti-seize and don’t over-torque them, so I was just careful and had no problem). 3 of 4 cylinders reeked of fuel (which, of course, just confused me. I was hoping for one - so now its hard for me to say what “normal” is. I guess 3 leaky injectors in 220K isn’t bad).

Anyway, I’m now in the garage with my fuel rail off and injectors out. No matter what I won’t be unhappy to have pulled it to clean everything - plenty of gunk in the hats on the fuel rail. There is nothing out of order visually, but my guess is that the real story in on the inside. My plan at the moment is to clean everything as best I can, reassemble the rail to the fuel lines - energize & look at the spray and leakdown. Other than that, does anyone have any suggestions either for what else to do and/or to look at to learn about the injectors are behaving? (I tested resistances which are fine).

If I can verify a problem, I’ve looked at the kinds of injector cleaning/testing companies suggested by stronzo. I may try that out to save a couple hundred $$ - but does anyone else have any experience with those things? Am I smarter just to pick up a set of new? ($300 minimum vs. $60 - 80 + time).

It’s not very difficult to see if an injector is leaking once you’ve taken them out. Just get a junkyard electric fuel pump and clamp a hose directly onto one injector at a time. Immerse the pump in a coffee can with fuel (or injector cleaner) in it and turn it on. If you see anything coming out of the injector it’s leaking.

If you want to you can actually operate the injector as well, just by switching 12 volts on and off to it. Some years ago I built a device to switch battery voltage on and off maybe 3 or 4 times a second, keeping the injector on maybe a tenth of a second each time. I use it, along with a junkyard pump to run a 50/50 mix of fuel/cleaner through injectors. You’d be surprised how black and cruddy the fuel/cleaner mix gets after cleaning a set of injectors. Warm, too.

Just be pretty careful with the battery and the can of fuel if you do this. Obviously, no sparks, or it’ll get nasty pretty quickly.

I think there’s a problem with the fuel pump check valve.

The fuel system on a fuel injected engine is a closed loop system. This means whatever fuel isn’t used at the injectors is returned back to the gas tank thru the control of the fuel pressure regulator. This gas passes thru the fuel rail which sits above the engine and is heated. As this closed loop cycle continues, the gas in the tank begins to heat up. This rise in temperature of the gas in the gas tank might be enough to prevent the check valve in the fuel pump from operating correctly. And this might be the reason why fuel the pressure drops under hot conditions.

Here’s what I would do to confirm this. Wait until the fuel level drops to a quarter of a tank and have a 5 gallon can of gas ready. Now do the hot condition fuel pressure test. If the pressure drops off, pour the 5 gallons of gas into the gas tank and redo the fuel pressure test. If the pressure holds, the check valve is being effected by the rise of temperature of the fuel in the tank.


Just to make sure I have that right - the idea is that the 5 gal of new gas immediately cools the fuel pump - yes? Excellent idea as always Tester.

Here will be the real question when I get it sorted out - unless it is actually causing a problem is there any reason to fix it? I.e. does it actually hurt anything. The only start up problems I’ve ever had are on hot restarts, b/c of my driving routine I rarely actually do one, and the problems I have had are really minor. I can live w/ it unless there is some other reason to fix it.