Batt. disconnected=fuel rail holds pressure, Connected=bleeds pressure

[brownfinger]

Like the title says...Does this make any sense to anyone? For the last year or two the car has been rougher and rougher on start-up. Finally got a FP guage (filter mount). Found out the rail wouldn't hold pressure overnight. Got a new FPR, too.
The other day I had the car in the garage, out of service for a bit. On a whim I disconnected the battery to reset the ECU. It stayed like that for about 48 hours. The following morning I noticed that it had actually held pressure overnight! By the following morning the pressure had actually gone up (ambient temp rose 20*).
Put the car back together, hooked-up batt., rail won't hold pressure more than a couple of hours again.
I'm mystified. The hard start is the least of my problems right now (unless there is a bad injector causing both symptoms), but I can't comprehend how this is even possible. How can disconnecting the battery make a fuel pressure leak go away when the car is sitting? Can a faulty ECU or relay partially energize an injector, or the pump, even when the key is off?
I haven't repeated the conditions to test if the rail holds pressure every time the batt. is disconnected, but this is the first time in 2 years the rail has held pressure overnight, and it held pressure for 48 straight hours.
Anyone ?

 

[crimsondragon]

Stock FPR with solenoid connected? It might have something to do with the solenoid if it's electrically related. It also could be the injectors. But really, fuel pressure shouldn't matter much. My pressure leaks down in about 5 minutes. As long as the car is hot, it'll start right up. Temperature has more of a say in start ups then pressure.

 

[brownfinger]

1993 NT federal: no FP solenoid, thus my confusion. I'm wondering if this is a symptom of an ECU failure. The only modification to my electrical system is a large capacitor in my stereo amplifier wiring. I wouldn't mind if all I had to do is remove that cap, but the cap has been there for 10 years. I've only developed this problem over the last year or two. The only way I can see how the battery is causing a pressure loss when the key is "off" would be if the injectors or pump are partially energized through a bad ground or a circuit shorted to the injectors/pump's ground.

 

[brownfinger]

not sure if this counts as bumping. I just finnished ruining some of my injector electrical connectors, pulled the fuel rail to change the leaky insulators. I left the fuel lines connected to see if I could view any leaks @ the injector. I see no harm in this with zero pressure. Thing is, after about 1 hour with the injectors disconnected the rail is beginning to develop pressure (ambient air temp is also climbing signifigantly today).
How the hell does that make any sense?
All 4 injectors read 14.1 Ohms (NT), all four injector plugs read 0.00 volts.
I guess I'll check for any voltage between each of the 8 wire terminals and ground.

 

[sniver]

federal emission turbo cars have a solenoid to bump up fuel pressure, to prevent vapor lock, on what the ecu deems hot days. NT do not have fr solenoids. There is also purge solenoid is located next to it. They are right to the left of the brake booster. The federal turbo cars lack a egr solenoid. Just fyi.

That fp solenoid has nothing to do with you losing fuel pressure though. I believe it blocks vacuum in order to raise fp. That said it cannot lead to total fuel pressure lose.

The fuel system could leak through(in order):
*the pump check valve ------------------------non-electrical related (possibility)
*o-ring on the pump to line connection---------non-electrical related (unlikely to change between pressurizations)
*fitting/line between sender unit and filter-----non-electrical related (unlikely to change between pressurizations)
*crush washers where you installed guage------non-electrical related (unlikely to change between pressurizations)
*line to rail/connections------------------------non-electrical related (unlikely to change between pressurizations)
*injectors---------------------------------------electrical related (possibility)
*fpr--------------------------------------------non-electrical related (replaced)

Are you able to repeat this little test? I am suspicious that what occured was a fluke.

I would start with:
*pull return hose that is leaving fpr and place it where fuel could drip into a cup. eliminate that
*What is the last time fuel pump was changed if ever?
*Fpr new, used? oem, aftermarket?
*original injectors?

get through all of that and post back what you find

 

[spawn87]

correct me if im wrong but doesnt the pressure leave the system the longer the system is not in use?...

have you messed with your fuel pump e.i: rewired the fuel pump, swaped for an aftermarket one?

disconnecting the battery is never the best solution its just a bandaid...i say hook up a logger to see if its only when the car is off...and do a scan for any codes that may have been ignored...just my two sents.

 

[brownfinger]

I was able to reproduce some of the test, sort of. I pulled the rail to replace the injector insulators, one was leaky. All four were original(213,000mi). Since the rail had no pressure I left both fuel lines connected. I had to unplug the connectors from the injectors to get the rail lifted out of the way (how do you slide out the little metal clips without breaking the plastic body of the connecter?). Bear in mind that the ambient temp. was rising from 15*F to 55*F with T-storms while I was doing this. As soon as the inj. elect. connectors were pulled, the rail started developing pressure, right up to 40psi. I was afraid the injectors were going to shoot out of the rail and poke out my eyes while spraying gas into my now-gouged eye sockets while I cleaned-out the seal bores. So I kept cracking the banjo open on the filter to releave the pressure. The cycle continued until I bolted the rail back on. The aforementioned weather made it impossible to really see which injectors were leaking. Condensation was forming like mad on every surface for 12-straight hours. Definately some injectors are leaking. They are orig. As soon as I re-connected the electrical plugs, pressure ceased building.
The only electrical mod to my car to speak of is a capacitor for the stereo amp. It's been there since 2000, this problem is more recent.
FP is original, and undisturbed. FPR is brand-spanking-new OEM Denso.
Also, I'm pretty sure the FP solenoid is a turbo-only thing.
My over-all debiltating problem seems to have been mostly solved by a coil-swap. I'll need to put the old one back in to verify. But, this fuel pressure thing still needs to be fixed, too. I don't think the fuel rail's worth of gas dripping into my C-case every night is doing my oil's integrity any good.
Thanks for replying.

 

[brownfinger]

disconnecting the battery is never the best solution its just a bandaid...i say hook up a logger to see if its only when the car is off...and do a scan for any codes that may have been ignored...just my two sents.

Battery was disc. for legit reasons, I just happened to look at the guage when I reconnected it. They're right next to each other. I FINALLY got Palm/MMCd. Datalogger is like reading tea leaves with a 1G. My coil was bad, and it essentially told me my O2 sensor was dead! I think. I tried to fix 5 different things at once that I wasn't sure were even broke, and something worked. 95% better, at least.
To flag a CEL on a 1G, the part needs to fail, AND disconnect itself from the harness while it's at it.

 

[dsmfa9nutter]

correct me if im wrong but doesnt the pressure leave the system the longer the system is not in use?...

Yep. Fpr's on dsms don't hold pressure after the car is turned off. Unless it's some goofy california emission thing. I'm not sure about that.

 

[sniver]

Fuel systems are designed to hold pressure, hence the check valve on the fuel pump to prevent pressure loss. It will lose some psi of pressure for some unit of time...it does leak, but it should only be a few psi short 8 hours later (overnight). And upon reading, your right, there is no fuel pressure solenoid.

Did you check the return hose to see if that is where leaking? Pull the gas cap in future incidents and see if it prevents unwanted rail pressure.

If there is not voltage at the injector clips then there is no way for injectors to leak when the connector is clipped on. Also I don't know the proper way to unhook the injector connectors. Mine were fubared before I got my hands on them.

Look at the picture i attached. it shows pin 1 on the injector connector has power when the ecu does, which in when the key is in the on position. From there the ecu triggers an injector by grounding pin 2 completing the circuit.

Check pin 1 and see that it does have power when the key in on , and has no power otherwise.

Next, with an ohm meter check pin 2 to ground. It should say ofl or out of limit. That is because there is infinitive resistance when there is no connection.

Try that and report back

 

[sniver]

Are the ecu fault codes the same an a turbo & nt? The data logger probably pulls numbers and looks in it program to see the meaning. That could very well explain the randomness. Aside from the fact of 1g ecu being unreliable.

 

[dsmfa9nutter]

Fuel systems are designed to hold pressure, hence the check valve on the fuel pump to prevent pressure loss. It will lose some psi of pressure for some unit of time...it does leak, but it should only be a few psi short 8 hours later (overnight)

Yes, they hold pressure when the car is on. I'm not sure what car you're driving that's holding 40psi after 8 hours of sitting but it sure isn't a dsm.

 

[brownfinger]

Yes, they hold pressure when the car is on. I'm not sure what car you're driving that's holding 40psi after 8 hours of sitting but it sure isn't a dsm.

NT runs higher pressure. 45 w/o vac is correct. the fuel system is supposed to hold at least some pressure, not full pressure, indefinately. There is no leak anywhere external. The mindf**k here is that BOTH times I noticed this phenomenon (fuel rail has pressure when it usually doesn't) there was a bizaar coincidence: The fuel injectors had no electrical connections because either the injectors were disconnected or the battery was, AND the ambient temperature was rising so fast it was like the rapture was coming!
The weather has been fubarred around the Midwest lately, 5* one day, 60* the next. It's hard to say what effect temp. is having on this when working in such unusual conditions.
I haven't disconnected anything specifically to test for this phenomenon.
My injectors have 200000+ miles on them. I think at least one is leaking. If you read my earlier posts in this thread, you'll see that all of the liquid condensation forming on my injectors made it impossible to tell which were/weren't leaking when I had the rail off of the head. The metal injectors were about 30*F, the air temp was 55*F, 100% humidity: every surface of everything in the garage was covered with liquid water.
When you first cold start it, it's ugly for 5 seconds, then it purrs to a fine high idle. It fires right up, then stummbles like hell, then tries to die, then Bing!, smooth high idle. This is only the first start of the day, when the FP guage shows 0psi. It takes 4+ hours usually for the FP to bleed down to 0. It shouldn't bleed down ALL the way.
I think my cold start goes like this: Engine fires rightup off of the tablespoons of liquid gas that have dripped down into the runners and cylinders, then it is flooded and tries to die. By this time the fuel rail has purged any air out and has finally developed pressure, and the engine is running right, provided it didn't die during it's initial stumble. If it did die, it fires up and runs right away on the 2nd turn of the key.
All of this may be a coincidence. Just leaky injectors. Maybe if I could bring the car into the house on a cold day I would watch the fuel pressure rise, only then to bleed back down, out of my leaky injectors. My garage is not heated.
I know FPR is good. Besides being brand new OEM, several other FPRs also did the same thing.
I could pinch-clamp the fuel hose between the filter and the rail over-night to test the pump's check valve, and rule it out. My guage is on the filter banjo bolt.
How do you test injectors to find the leak? Just look? Hook up a compressor to the fuel inlet?
Anyone know?
Sniver: NT/turbo: codes are the same, but I haven't had any. Logger showed no O2 sensor voltage because bad coil wasn't burning the air in the chamber; O2 sensor was reading correctly that there were assloads of unburned air in my exhaust. ECU's solution was to max-out all fuel trims. Silly ECU. My brain get constipated from electrical diagrams. I think I've already checked what you're talking about and got correct results. I'll have to get back to you on that stuff.

 

[sniver]

Hmm ...I bet the injectors will solve the fuel problem. They can be bought fairly cheap on the classifieds due to all the upgrades that shun the tiny injectors. I"m also curious of a couple other things that affect start up. First compression test...I don't think I already asked. second is do you notice any exhaust signs? (namely white cloud at start up with coolant consumption..)


This pic is what the fsm says, notice "no fuel supply", think leaked pressure. fix the leak , save the world! But eliminate all the possibilities and tell me you did and how.

 

[brownfinger]

How time flies...I've occasionally got to let the car be for a little while. There is much else to do in life, like fixing and selling other cars so I can buy more 1G DSMs! And food and sex... Plus it's cold out.
Something I did seems to have helped a lot. The car runs and starts much better now. I did too many things at once to know what did the trick. Pulled fuel rail, replaced injector seals. Loosened and re-torqued TB bolts at that time. Tightened manifold mounting bolts and cleaned PCV valve while access was good. Swapped coil for a different one. Much easier with fuel rail out. Cleaned MAF element. Reset ECU. Swapped O2 sensor for a different one. Resoldered/re-insulated some crumbly leads in the o2 sensor harness/plug. That was all on the same day.
Since then, replaced swiss-cheese exaust manifold with a new one. The fuel trims are all still very high, but I also put the previous coil back in, to see if I can make it run like poop again. I think I did. Brand new coil I ordered arrived last night. It will go in today. The old coil had green-white corrosion inside the plug-wire sockets, and the other used one I tried (the original one to the car) had 200,000mi on it. Both coils' primary resistence measured higher than the spec in Haynes manual.
Me and MMCd will patiently see what happens.
It's been a few years since a compression test, but the car hasn't had too many miles in those years. The last test was something like: 170, 165,175, 170. It had about 190K then, and it's at 213K now. No signs of head gasket leaks. All disappearing coolant is accounted for on garage floor/splash shield under radiator. Got a new upper coolant hose with the coil.
I agree about a leaky injector. I just wish I could pinpoint which one it is. I think another set of 4 used ones has a probability of at least one leaky one again. I'd like at least a slight degree of certainty and precision.