injector pop?

[Bullrack]

12mm VE and 14mm VE, both fed with an Aeromotive A1000, never had the issue you describe. It concerns me that anyone would think that the cylinder pressure is greater than injection pressure, ever.

Yea, I'm thinking if cylinder pressure ever exceeds pop pressure, you've got bigger concerns.

 

[BC847]

Yea, I'm thinking if cylinder pressure ever exceeds pop pressure, you've got bigger concerns.

That right there makes me think y'all perhaps are misunderstanding what I'm suggesting.

- At the end of the injection event, the incoming fuel flow drops to what ever the residual pressure in the injector tip might be. At that point, certainly, the needle goes back into it's seat.
- In that context, at that split second, with side-stepping a WOT, the turbo(s) are still spooled presenting full pressurized charge-air to the cylinders.
- The next compression stroke comes up and further compresses that full boost charge-air.

In that instant, is it possible to lift the needle just enough so as to allow some of that compressed charge-air to leak into the nozzle area, behind the seat.
- I realize that the area of the needle, that the compressed charge-air sees, is a LOT smaller than that area of the needle, that the incoming pressurized fuel sees, to lift the needle. (That area of the needle exposed in the total cross-section of the orifices VS that area of the piston (if you will), on the needle that the fuel lifts it with).
A pneumatic lift, compared to the normal hydrolic lift.

I'm NOT talking about when the fuel injection event is occurring, the compressed charge-air overcomes the injecting fuel pressure allowing it to flow back into the nozzle while the needle is off it's seat. The engine wouldn't run for lack of fuel!

I'm talking about AFTER the injection event has ceased. No fuel flow to the injector, the delivery-valve is closed (the H/R is dealing to the other cylinders).

- Perhaps a soiled or eroded needle/nozzle interface is leaking? Perhaps rolling off the throttle keeps a minimum amount of fuel purging the nozzle of any air till the charge-air calms down?

 

[Smokin ACE]

I've had this same problem. I'll explain my current setup and my experience with this problem. I have an Airdog II 200gph with full 1/2" lines from my custom fuel sump to the intlet of the VE. It is set at 14 psi for now and will not drop below 11 psi at WOT. Lack of fuel flow to my VE I can guarantee is not my problem. 200gph + 1/2" lines can flow a lot of fuel in a hurry (probably overkill for a VE) I remember testing it out to get my pressure set before I hooked the line to my VE, I kinked the hose after the pressure sensor to cause some resistance and fuel was coming out of the hose just like a garden hose with the valve all the way open when I turned the pump on. Alsothe incoming fuel should be "air-free" since its going through the Airdog water/air/fuel seperator. Then it comes to my VE, a 12mm pump with the full power screw bout to runaway and no afc so its running full fuel all the time, from there it goes to my POD 4 hole injectors. I've had this same problem with my PODS (260 bar) and some 5x13s (245 bar) so injectors didnt seem to change the problem for me.

I never had this letting of quick and die problem til I ran a big single turbo. I ran an ATS Aurora 5000, a 71mm single that would push 50 lbs of boost at ease. With all my other turbos I could only hit about 40 lbs and never had this problem except for once while truck pulling, I was running an Aurora 3000 (58mm) and let off at the end and the truck completely died. I was in a panic and cranked the motor over for a few seconds then it fired up reving up to about 2500 rpm right off the bat and blowing smoke for a few seconds as if it was cleaning itself out then came back down to an idle luckily and ran fine. While running my bigger turbo and letting off quick at 50 lbs of boost I had my truck die once or twice, but usually a few cranks got it running again without bleeding the injectors, it would run rough for a bit then slowly clean the air out and run smooth again with a few taps of the throttle. I even had it just come to a sputter a few times rather than completely die when letting off too fast, a few simple taps of the throttle got it running smooth once again as well.

I remember asking this question on DTR as to why this happened. I have heard different things on this subject. I heard that high cylinder/boost pressures combined pushed back through the injectors like BC is explaining. I've heard that from quite a few people. I have also heard that after letting off the pedal after WOT all the fuel has nowhere to go but through the return line and back to the tank leaving a small time gap where there is no or not enough fuel to keep things running or running smoothly til everything catches back up. I know that VP truck have or can have this same problem, and I thought I've heard of a few P pumps doing this as well if I'm not mistaken...

I've just been told and heard to let off the pedal slowly or "roll off" rather than snap off after a hard pull. Not only does this keep your truck running smoothly but its easier on turbos as well. I've heard even giving a few romps of the throttle after a hard pull to clean things out will cure this problem. Since I have been doing one or the other I haven't really had this problem since.

I'm not saying what I've heard or done is right and is the right explanation, but my actions above have cured the problem for me. I am definately subscribed to this thread to find out the real mystery behind this.

 

[Smokem]

That right there makes me think y'all perhaps are misunderstanding what I'm suggesting.

I understand what you are saying, and I am still saying no. The same issue is present on the VP44 with migh higher injection pressure and opening pressure of the needle.

I have an Airdog II 200gph with full 1/2" lines from my custom fuel sump to the intlet of the VE. It is set at 14 psi for now and will not drop below 11 psi at WOT. Lack of fuel flow to my VE I can guarantee is not my problem. .

We use 5/8" line and an A1000, no more issues, in several cases.

 

[Bullrack]

I have to agree with Weston here, it's strictly a rotary pump deal.

 

[Smokin ACE]

I understand what you are saying, and I am still saying no. The same issue is present on the VP44 with migh higher injection pressure and opening pressure of the needle.



We use 5/8" line and an A1000, no more issues, in several cases.

what does an A1000 flow? and might as well use a garden hose for a fuel line:Cheer:


Here is my theory I was thinking about today, not sure if its anywhere close to a legit reason but I was just pondering today. So I am thinking out loud...

If you think about it all that cylinder pressure has nowhere to go but through the very small injector holes. High cylinder pressure (not as high as injection pressure) being pushed into the small holes of the injectors would create even higher pressures inside the injector holes. Its like putting your thumb over the end of a garden hose, it will create higher outlet pressure from the restricion. You take the area of the pressure in the cylinder and then pack it into a few small injector holes, the pressure inside those holes is going to multiply rapidly. So you would think that high of a pressure (being multiplied by going through the small injector hole resistance) to push back through an injector after the injection event until it is met with fuel again to push that air back out.

Correct me if I'm wrong, I'm just thinking out loud

 

[Bullrack]

what does an A1000 flow? and might as well use a garden hose for a fuel line:Cheer:


Here is my theory I was thinking about today, not sure if its anywhere close to a legit reason but I was just pondering today. So I am thinking out loud...

If you think about it all that cylinder pressure has nowhere to go but through the very small injector holes. High cylinder pressure (not as high as injection pressure) being pushed into the small holes of the injectors would create even higher pressures inside the injector holes. Its like putting your thumb over the end of a garden hose, it will create higher outlet pressure from the restricion. You take the area of the pressure in the cylinder and then pack it into a few small injector holes, the pressure inside those holes is going to multiply rapidly. So you would think that high of a pressure (being multiplied by going through the small injector hole resistance) to push back through an injector after the injection event until it is met with fuel again to push that air back out.

Correct me if I'm wrong, I'm just thinking out loud

It's all about pump recovery times! The rotary pumps don't keep as consistent pressures. The P7100 doesn't have this issue. Just the VE and VP.

 

[Smokem]

Why would cylinder pressure not open a pintle style injector then? They have much lower seat pressures, and are completely open to cylinder pressure.

 

[bgilbert]

A1000, 5/8 supply, 3/4 pickup from bottom of tank here. Never had this issue. With another truck it had 1/2" from bottom of the tank to the inlet of a low pressure piston lift pump. Made dozens back to back passes at the local 1/8th mile drag strip, along with hot rodding around town etc, never had this issue...?

 

[Cumminsfever]

Why would cylinder pressure not open a pintle style injector then? They have much lower seat pressures, and are completely open to cylinder pressure.

You bring up a good point.

I'll supply you with the answer- Delivery valve.

 

[BC847]

A1000, 5/8 supply, 3/4 pickup from bottom of tank here. Never had this issue. With another truck it had 1/2" from bottom of the tank to the inlet of a low pressure piston lift pump. Made dozens back to back passes at the local 1/8th mile drag strip, along with hot rodding around town etc, never had this issue...?

I don't have a fuel supply pressure problem. I have the fuel pressure sensor in the regulator and set for 12psig. Full throttle has it dip to no lower than 11psig.

The suggestion of the DVs being the culprit is interesting as I read some stuff in the Bosche manual last night where they were talking about the different designs and the benefits of each. In one instance, blow-back in the injector was mentioned (I can't remember the exact term).

 

[Smokem]

The suggestion of the DVs being the culprit is interesting as I read some stuff in the Bosche manual last night where they were talking about the different designs and the benefits of each. In one instance, blow-back in the injector was mentioned (I can't remember the exact term).

The P-7100 holder has a valve known as "return-flow restriction", even when you switch to a holder without this valve, the issue you speak of is not present.

 

[fatty]

A1000, 5/8 supply, 3/4 pickup from bottom of tank here. Never had this issue. With another truck it had 1/2" from bottom of the tank to the inlet of a low pressure piston lift pump. Made dozens back to back passes at the local 1/8th mile drag strip, along with hot rodding around town etc, never had this issue...?

My brother "soggy" used to have this issue with an A1000 and Scheid 6x16 injectors with a silver bullet on his '92. Since he got the engine and IP rebuilt, and now has SDX 5x18 injectors it hasn't been happening.

 

[ram99v]

I understand what you are saying, and I am still saying no. The same issue is present on the VP44 with migh higher injection pressure and opening pressure of the needle.



We use 5/8" line and an A1000, no more issues, in several cases.

There is two things I know for certain;

1. It's not cylinder pressure reversion.
2. A higher flowing supply system resolved the issue in all instances I have seen.

Cylinder pressure higher than injection pressure? I guess I do not understand how some people come to these conclusions. Exhaust gas entering the nozzle back through the spray orifices is common and known as soot blowback, this is caused by the needle hanging in the guide.

I had this issue with a FASS on a VP truck, switched to an A1000 and the problem was resolved, did the Aeromotive pump increase injection pressure, or was the fuel supply just inadequate before? Seems like a pretty easy question to answer.

We so no pressure drop with the FASS, I just feel it was not enough volume. The truck would flat die/vapor lock after a hard pull, many had an opinion or a reason, some did not believe it, but the new setup resolved it. I tore the injectors down and there was no soot blowback on the needles, this was many years ago.

How does added volume help again..........lol

5/8 line to a 1/4 hole that helps.

You of all people should know better than that.

Thats like putting comp delivery valves in with stock injector's :badidea:

*bdh*

 

[Smokem]

You tell me, since you seem to have a chip on your shoulder.

 

[ram99v]

looked like potentially bad information:what:

 

[Smokem]

How does a runner intake improve flow on a cylinder head? It's the same concept, a larger available volume during recovery time. Seems like it is information that has proven itself in the real world several times, and only possibly bad information to you.

 

[ram99v]

Ya I worded that poorly; should of said

looked like potentially miss under stood information.

I'll go with that ..........not bad....lol :bow::bow::bow::bow:

 

[JQmile]

Finally, a VE argument I'm not in on. :lolly: For the record, I've never had that problem, but I roll off the throttle, and I have a pretty good fuel system.

 

[soggy]

This happened to me at after i cranked up the pump and put a HE341 (40 psi) on, everything else was stock.
Put an A-1000 on, still did it.
Silver bullet (50psi) went on next, still did it.
6x16s went in, still did it.
Rebuilt injection pump and it went away. Anyone have the problem go way after a new IP?

Setup now is a-1000, 363 (45psi) 5x18s. Slightly lower compression.