Fuel Pressure Drops after shut off

[DSMopar]

That's why I suggested bailing wire, but zip ties are pretty strong.
43/ 4 = 10~psi across each injector, think of when your doing a BLT and that coupler blows off at 20psi...though that is a larger volume to fill. Just be careful.

Holy shit don't listen to this guy....


Your pump is fine

Your injectors are likely fine

What are you using to tune with? You DO know your cranking pulsewidths are the same as your smaller injectors were unless you've done something to compensate for this.

Edit: just noticed you're using ECMlink, what did you use before this? details...

 

[LiquidX]

What are you using to tune with? You DO know your cranking pulsewidths are the same as your smaller injectors were unless you've done something to compensate for this.

Edit: just noticed you're using ECMlink, what did you use before this? details...

I had stock injectors with the AFPR and pump and did not have this issue. I then installed ECMLink with stock injectors and the fuel pressure was staying in the system. Once I put the FIC 1250's in, I've been loosing fuel pressure upon shut off.


Side note, 1-2 quick cranks to get the pump pumping, I can start the car right away like I used to be able to.

I did just see this "43/ 4 = 10~psi across each injector, think of when your doing a BLT and that coupler blows off at 20psi..."

It would still remain 43psi at each injector as the whole rail is pressurized at that amount so each tap into the rail will see that pressure.

 

[supravw]

Just to throw this out there, when I was using ecmlink with some 1000cc injectors it would take about 20 seconds or so before I could let it idle on it's own. I've switched back to a stock setup and same thing. I eliminated all of the throttle body sensors other then the tps so that's part of the reason.

Sense you have link you can mess with the fuel richening compared to coolant temp. If you richen it up some while the motor's cool that should help your idle some. I believe it's under the direct access but I'm not positive.

 

[LiquidX]

I got the idle fine, that was a different issue. My issue is that my fuel pressure is leaving the rail very quickly.

 

[viprez586]

That fuel pressure comment was a word of caution.

Anyway I bet it's the injector. Fuel pressure has nothing to do with what is controlled via pcm.

If you have a better way of testing a leaking injector in your "backyard" please wow me with your master-tech ability.

 

[LiquidX]

Jake,

I recieved an email from FIC

"I purchached a set of 1250 Bluemax injectors from a vendor for my 2g DSM about a year ago. I just got them put in a couple days ago since my car was without an engine the whole time.

After installing them I have noticed that my AFPR pressure reading drops from 43psi to 0psi in about 40 minuits or so. It only takes about 5 minuits to drop from 43psi to 20psi.

Is there any way that I could get them tested for leaking or is there any way I could do that at my home?

Thanks


"HI

Pressure drops at the rate that you are describing are not unusual and would not be of major concern to me unless you seeing other problems with the injectors."


I replied with another email stating that I have had the same setup for a long while with not pressure drop but as soon as I put the injectors in, pressure was dropping. I'll see what they say if they may deem it leaking.

 

[ramsack]

Get one of those things that are like vise-grips used to pinch hoses and pinch the fuel feed hose before the rail. If the pressure still drops then it is either your AFPR or injectors. Realize that liquid does not compress, so you will not really see any liquid leaking out of anything before it evaporates!

 

[Calan]

My AFPR pressure drops pretty quickly after turning the pump off, but I have no related drivability issues. This is pretty common with aftermarket AFPR's, although the actual reasons for it seem to be a subject for debate.

There are several threads on this topic that have been started over the last few years, but no definitive conclusions that I know of. As for the larger injectors, they are just notorious for being finicky, and take a while to dial in....but I really don't think they are related to the fuel pressure drop. (I saw it even with smaller 650's).

I wouldn't worry about the pressure dropping at the rail after shutdown, assuming you get that idle dialed in where you want it and the car continues to start.

 

[LiquidX]

I would pinch the line if it wasn't all Braided SS.

If I don't prime the fuel pump about 2 times by quick key turns then it'll take about 15 seconds for the car to start.

 

[joescool2008]

My AEM FPR drops to 0 almost immediately after i shut off my car, from my experience your coolant temp sensor wiring is bad or the sensor itself is bad. The wiring is in a hot spot and very brittle, i've had this issue with almost all 1g's I have ever worked on.

 

[Calan]

If I don't prime the fuel pump about 2 times by quick key turns then it'll take about 15 seconds for the car to start.

I still think you're just off a bit with the Link calibration, or maybe something else is messing with the start. I have no pressure in my rail either, but the car starts with just a couple of cranks. This is on the same injectors as you are running, with an Aeromotive AFPR and Walbro 255hp pump.

 

[LiquidX]

Craig, I understand what you are saying with setting the idle but with my stock injectors there was no pressure drop at all. This is the reason why I think they are leaking.


Temp sensor is fine. If that was broke then you wouldn't start at all.

 

[ramsack]

I would pinch the line if it wasn't all Braided SS.

The stainless braided is just on the outside of the hose. You won't ruin anything pinching it.

 

[LiquidX]

The stainless braided is just on the outside of the hose. You won't ruin anything pinching it.

Positive this won't hurt anything? I was under the impression that damaged braids could cause a kink or something like that.

 

[ramsack]

Positive. It will need to be bent back because it will hold shape, but that can be done by hand.

 

[Calan]

The stainless braided is just on the outside of the hose. You won't ruin anything pinching it.

I would be careful with this. I've pinched some with no issues, and I've also scarred some pretty badly that didn't recover. It won't physically hurt the hose, but it can permanently deform the braiding which isn't very attractive.

On decent SS line, you should be ok...just use a rag or something to protect the braiding. On less expensive stuff or anything that is coated (like most SS brake lines), I would find another alternative.

BTW - In my opinion, the most likely cause for pressure bleeding from the fuel rail is the o-ring seal at the top of the outlet "funnel" at the fuel pump. As soon as I switched to an aftermarket pump, I started noticing the fuel rail pressure drop...and I've seen it in varying amounts with different pumps. IMHO, it is damn near impossible to get a positive seal where the pump meets the outlet tube. I just don't worry about it anymore, since the car starts and runs fine...outside of the normal occasional DSM head-scratching weirdness of course.

 

[LiquidX]

Well I went and pinched the line.

The fuel pressure still drops with the line pinched but once I pull the vice grips off, the fuel pressure goes from 20psi instantly down to 5psi or less.

Now I'm unsure of the issue. Is the check valve in the fuel pump bad that it's slowly allowing fuel to go back into the tank? It's possible the injectors are leaking too.

I dunno, I'm just all confused now after that test...

 

[Calan]

With the line pinched, you are separating the rail from the pump side of the tank, so pressure is holding through the AFPR and return line (mostly). When you release the pinch, pressure is flowing back toward the outlet side of the pump and into the tank...past the o-ring at the pump outlet that I mentioned up there ^.

 

[LiquidX]

I know the AFPR is not to blame. The pressure still drops from 43 to 20psi with the pinched line. Unpinch it and the 20psi goes to 5psi (or lower) instantly.

 

[joescool2008]

Craig, I understand what you are saying with setting the idle but with my stock injectors there was no pressure drop at all. This is the reason why I think they are leaking.


Temp sensor is fine. If that was broke then you wouldn't start at all.

It could be giving a bad reading is what i'm saying, it doesnt have to be broke and I'm familiar how it will not start without it.

 

[ramsack]

You are losing pressure because you are giving volume back to the fuel line from being pinched. It doesn't take much. But seeing as how it held while being pinched I would suspect something at the pump end of things.

Calan, what about when people just cut that funnel off and use a hose with clamps to attach the pump? Would one expect pressure loss then? I have a 255HP installed that way, and when I had my stock regulator on I would sometimes lose pressure instantly, or it would sometimes take days to drop at all. Now with my AFPR it leaks down almost instantly. But I'm more worried about the times before with the stock FPR. My car has no tuning mods done and it still takes forever to start.

 

[viprez586]

My AEM FPR drops to 0 almost immediately after i shut off my car, from my experience your coolant temp sensor wiring is bad or the sensor itself is bad. The wiring is in a hot spot and very brittle, i've had this issue with almost all 1g's I have ever worked on.

Your FP shouldn't drop to zero immediately after shut-down. That's the symptom of a bad fuel pump check valve.
Highly unlikely with the coolant temp wiring for the OPs situation.

Well I went and pinched the line.

The fuel pressure still drops with the line pinched but once I pull the vice grips off, the fuel pressure goes from 20psi instantly down to 5psi or less.

Now I'm unsure of the issue. Is the check valve in the fuel pump bad that it's slowly allowing fuel to go back into the tank? It's possible the injectors are leaking too.

I dunno, I'm just all confused now after that test...

It's normal for it to slowly bleed off. Every car designed does not keep fuel pressure up for hours upon hours, why?
Think of parked cars. Say some electrical short occurs in the engine bay(happened to a Ford Focus owner last week I know), or the car is hit in some way, shape, or form.
The manufacturer designed the fuel pressure to bleed off after an hour or so, so that it does act as an accelerant or "fuel" to a fire if one were to occur.
To my understanding this check-valve slowly opens to a full state. Once you release the vice-grips after the determined time the check-valve has already opened to it's certain "percentage" that it would of had no vice-grips been placed there. Of course the fuel pressure directly affects this time period I'm sure - but not in full scale.

It just dawned on me how to test the injectors a super easy way.
Key on - engine off.
With dsmlink, datalogger, etc - whatever is easiest you want to go to injector test.
Watch you're fuel pressure drop with the command of each injector test. This would at least verify they are opening properly(or at least not clogged).
You may have to run a key cycle or two between each test of the injectors to get fuel pressure back up to "base".

Only problem I can think of is that they will all bleed down the same or too long(down to 0psi) to really verify any variance in injectors.

 

[Calan]

Calan, what about when people just cut that funnel off and use a hose with clamps to attach the pump? Would one expect pressure loss then?

Hmmm.... no idea as I've never hooked one up that way. I wouldn't think so, as long as it was a good connection. In that case I think pressure would be bleeding off somewhere else.

I just know that on both my car and others, that o-ring happens to be a common leak point.

 

[LiquidX]

Craig, I am starting to agree with you that there might be a tuning issue as well. If I prime the pump once I have a horrid time trying to start. Prime it a second time then I can just about start right away.

I had set my idle to 750 both logged and selected for ECMLink to idle there and it was causing me to stall out now and then when pressing in the clutch to get the engine to idle from a roll. My vac. reads 15inHg at 750rpm but 18-20inHg at around 900-1000rpm.


Thanks again for discussing the information with me over the phone too.

 

[Calan]

Thanks again for discussing the information with me over the phone too.

NP, although I don't think I was much help.

Try this...Turn the ignition on (without starting), connect Link, and start a log. After 30 seconds or so (and with the log still running), start the car. Let it idle a minute or two and then post up the log.

I'm curious to see what it looks like just before and during starting. It would be interesting to have versions of this type of log when it is both cold after sitting a while, and warmed up.