VG30DET wont pull RPM after warm up.

[tgsracing]

I have a sand rail with a VG30DET JDM motor in it and after a few seasons of running well an issue has started that I can't seem to figure out. When I first start the car it seems to drive normally pull through the RPM range and generate about 9psi of boost, after a few minutes of driving around it gets to a point where it seems to lay over when you go to WOT, partial throttle is still very driveable and no starting or idling issues. I thought I the fuel pump may have been going away so I put a new pump on it, no change, then I thought the pressure regulator was going bad as it did not seem to be returning fuel to the tank idling as it should be, more of a dribble. I changed to an aftermarket fuel labs regulator with a gauge and the proper boost reference ports. The pressure is set at 45 with the boost reference un hooked and the intake line capped. Same issue when cold start up it is returning alot fo fuel but after drivign around fuel seems to be dribbling in. I have blew the lines out several times bypassed the filter, changed filter all with the same result. This engine is run with an older link plus ECU assuming open loop as there is no MAF or O2 sensors to change the tune if there was a wacky reading. The only thing I have not changed in the fuel system is the injectors however, never puffs out black smoke, misses, or anything to make me think one is stuck open or closed. I am wondering if the fuel return is just a coincidence and throwing me down a rabbit hole thinking fuel system related. I have read about intake leaks maybe causing the engine not to RPM but again works great upon cold startup. Would a faulty worn out CAS start to cause these issues as its gets hot maybe throwing the timing off? Would a bad temp sensor cause this? I know there are 2 on this motor, one in the block and one in the aluminum water line. I understand not being able to get into the computer (older ECU and dont have the PC link nor a laptop) might be an issue but does anyone have any ideas for me? Any help is greatly appreciated.

Thanks,
Dan

[tgsracing]

I would also like to add I changed the PTU with a known working one and the same result incurred.

[tgsracing]

I would like to add to the previous post in hopes someone can possibly help me, I put a brand new fuel pump on it and the same issue occurs, upon building boost the engine misses and cuts out, I validated that the fuel pressure drops to nearly 0 when any boost try's to build. I bypassed the computer and ran a switch directly to the battery for the pump and same issue. I took off all the fuel lines and blew through them and nothing appears to be blocking the pressure side of the fuel rail. Would bad injectors cause this issue? The car always starts great, idles great, and revs up clean. I removed the filter for the sake of checking things out and I can validate there is great flow from the take to the pump as I have a clear filter and it always stays full of fuel. Again any help is appreciated.

[Ace2cool]

The only way the boost would cause the fuel pressure to drop to zero is if your AFR is not correct and is telling the injectors to pull 100% duty cycle and your fuel pump can't keep up. That being said, on an open loop circuit, you can't really rely on anything to tell you that an injector hasn't failed. Are you using the OEM pump? What about the fuel damper? Is it functioning correctly?

[tgsracing]

It is not an OEM pump it is an MSD pump rated at 43gph, I have ran this pump for 2 years however, I bought a new one to rule that out. When say fuel damper are you referring to the regulator? That is also new, I was not able to find a factory replacement for the DET motor so replaced it with a fuel labs adjustable one with a boost reference. I have set this all over the place in trying different things but no success.

[Ace2cool]

It's gotta be losing pressure somewhere. I'd look at it like a circuit. Feed and return, with a device causing drain. Try isolating possible causes. Run a line from the pump to the filter for testing and see if that changes anything.

Here's the damper:


It helps improve fuel delivery. Also check your vacuum lines running to the regulator and the damper.

[tgsracing]

Ok, I do not appear to have a damper and the fuel rail is slightly different because it is a DET. I took the rail off and blew through it all but didn't remove the injectors because they are the push lock type and they have been on there a long time. I have yet to take it out and try it again since I put it back together. I will say something definitely appears to be causing blockage on the pressure side but nothing came out when I blew through the lines.

[Ace2cool]

DET? As in dual overhead cam and single turbo? Shouldn't make a difference for a fuel delivery system. All the rails for the VG30DE(TT) should be the same, other than new vs old style differences.

[tgsracing]

The rails are slightly different but at any rate I took the whole rail off and apart and blew through it. I left the injectors on it as they were the push lock type and not totally sure how they come apart. Still the same problem and I'm not putting new injectors and that is the only part of the fuel system I have not changed however they are really hard to find for this motor and not cheap. Would a bad coil(s) cause a misfire under a load? It starts and idles great and was reading some other stuff online where a bad coil can cause this, again runs smooth at idle so doubt I will unplug one and notice a difference. Is there a way to bench test the coils using a multimeter? You have to pull half the intake off to check the drivers side so putting a known good one on various cylinders would take forever. Just wanted to get some thoughts about this.

[Ace2cool]

Sorry, I must have misread your question, and/or only answered half of it.

There is a tolerance for the coils, and it can be found in the FSM, but the easier way to do it would be to wait for it to "act up," and then pull connectors one at a time, and when you find the one that doesn't change anything, that is your culprit cylinder. When you find that one, swap the coil pack with another coil pack and see if the problem moves to the new location. If it does, it'll be a coil pack. If it doesn't, more than likely injectors.

But IMHO, if you are losing all your fuel pressure on a new pump, that'd be a different issue than a stuck injector, and you'd most likely be flooding a cylinder completely to the point of fuel coming out of the exhaust and having a noticeably wet spark plug.

Could you post a picture of your current fuel delivery setup and/or a diagram? I'm having a hard time visualizing the setup without it actually being in a Z32, haha.

[tgsracing]

I have read about pulling the coil connector and see if the engine changes however you can only do that on one side as the turbo piping and throttle bodies need to come off to get to the other 3 coils. It does appear to idle and rev fine and just a miss when your on the throttle. Below is a link to what the fuel rail looks like that I found on Google images
http://s265.photobucket.com/user/bakaka ... 0.jpg.html
There are a few other pictures to the left and right. But essentially out of the tank it goes to a fuel filter, then to the pump, the line directly into the fuel rail. The fuel rail has 2 return lines that feed into the regulator, regulator then returns to the tank. I have never checked but would say based on feel the inlet line prior to the rail has much more pressure over the lines after the rail to the regulator and they should be the same. Seems like something is dead heading the fuel in the rail however blew through it several times and since fuel returns through the injectors those might be the problem. Problem is as you can see in the fuel rail pics, all the injectors would have to be stopping fuel for it not to bypass.

[Ace2cool]

I think we've found out why you don't have a damper. You're not a VG30DETT, you've got a VG30ET, which is out of an '80s 300ZX, or Z31. Also why I was wracking my brain trying to figure out what was going on, haha. The VG30DETT has side feed injectors only. The VG30ET has.... something different. I think they're top fed and side return.

If it idles fine though, it probably isn't an injector. Those are usually all-or-nothing type things. Now, a coil pack going out can get worse with heat, but that doesn't explain your fuel pressure loss. You are taking your readings from the FPR with gauge, correct? This really is a tough one. I'm going to move this to the old farts forum and update the title so that we can have more knowledgeable eyes look at it.

[tgsracing]

Yeah, it is the JDM single turbo version and correct I have been referencing my FPR for fuel pressure.

[madmax_087]

Sorry, no help as I am having a similar issue, but I'd love to see the rail!!

PICS!!

[evildky]

tgsracing:I suspect the problem is within your" links plus ecu", and this is the first I've ever heard of them. I would suggest you do some datalogging and figure out what is changing. Could be as simple as a tuning or enrichment setting. If this system has knock detect are you detecting knock? Getting good consistent engine and air intake temps? On stock and many aftermarket systems reading a loss of temp sensor defaults to vold which can cause a rich condition to the point of flooding to the point of stalling. Step one is definitely get connected to that management system and start checking that it's receiving all the correct signals.

Those are dual feed injectors. Dual and side feed injectors are a cruel joke played on us by nissan engineers, and if one of the bottom seals goes you dump unmetered fuel into the intake runner, but since you can runs fine until warm I doubt this is the issue. A pic of the engine would help us verify what engine you have.

If this is a VG30et the cas is located inside the distributor and they can also fail when warm, again with that engine management system hooked up to a computer you can see if the signals are dropping off, in stock form there are 2 signals one is every degree and the other is every 60, I have no idea which your system uses megasquirt generally just uses the 60 degree signals. Then there is the PTU or ignitor which can also fail intermittently when hot.again if your system uses the stock ignition bits.
If it's a vg30DET is has Coils on the plugs fired by a 6 channel PTU (or ignitor) of course you system may or may not use this driver or it's own onboard which may be sequential like the OE or wasted spark as most aftermarket systems are.

Ace2cool: I have actually seen multiple Nissan/Datsun fuel pumps fail upon boost. The FPR see's the boost raising fuel pressure causing the fuel pump top work harder and if the pump is nearly dead it heats up and shuts off, once cool often restarts.

[tgsracing]

Thanks for the response, I do have some pics of the motor however, I am unsure of how to post pics on this forum. I don't have the proper equipment to hook up to the link ecu but I know a guy around here who offered so will have to give him a call. I did ponder the PtU but after reading up on these I always carry a spare and it acted the same. I believe the CaS is the same as say a 1991 VG30dett as it is in my motor and given the price I have not been willing to purchase one to try. It could very well be the ECU or something related I have just not had a way to get into it. If someone can share how to post pics I will be happy to take pics of whatever's needed.

[sx moneypit]

Here ya go.
how-to-post-pictures-using-photobucket-t521110.html

[evildky]

For reference this is a VG30E, There are numerous variation on the intake plenum but the valve covers and timing covers are the same and they use a distributor to the front right of the engine

This is a VG30DETT, again the intake might be different but the cam covers and timing covers should be basically the same. This one has the CAS off in this pic notice the silver hole in the right front timing cover, thats where the cas goes, it keys off the exhaust cam.

[tgsracing]

Correct my long block is the same as the DETT in the picture on the bottom with the intake and turbo setup being different. I will sign up for photobucket, do you guys use a "throw away" email or my standard, I have seen people saying different things regarding privacy.

[tgsracing]

Just figured out how to get some pics up, but here is the engine, I have a few more I will post later. Let me know what other things you may want to see now that I figured it out.

[tgsracing]

Here are a few more pics

[evildky]

Yup that is a VG30DE long block, which is similar to the engines found in the Z32's J30 and whatever else. Now I real curious about your engine management as this engine has variable valve timing and COP ignition.

[tgsracing]

Again it's an older setup link plus G1, here is a link to their older stuff on their website just for reference http://www.linkecu.com/support/document ... umentation

[Ace2cool]

That's out of a Maxima, or rather, the Japanese RWD version, the Cedric/Cima. It was also available in the Leopard and the Gloria. No wonder this has been so confusing. This engine was never sold in the states.

[evildky]

depending on the model looks like you have knock support which could be the issue, looks like it uses a proprietary i3 channel ignitor in wasted spark configuration unless someone adapted to the 6 channel nissan unit. Whatever your problem is, step on is getting that system hooked up to a laptop with the tuning software.

[tgsracing]

Sorry for not posting been busy and have not had much time to get back into the project. One of things I did do is I took it to a local guy that seemed to have some knowledge about these motors and after watching the fuel pressure closely, he stated that the pressure would drop prior to the engine misfiring pointing back to a for sure fuel problem. He had a stock regulator that we put on and the same problem occurred, then he wanted to change out my new pump as well to rule that out. Well in the short ride we took it did not miss and the fuel is still returning to the tank properly. Mine was a MSD 2225 that I ran for 2 years and I replaced it with the same model, it is rated to 500 hp. His is a Walbro pump, I am not sure of the specs he stated it was one of their biggest ones also rated to 500hp. I have yet to take the car out for longer duration with the Walbro pump to really test that, I will try to get to that in a week or so, maybe my old MSD pump was truly bad and got a dud with the new MSD pump however, nothing changed when i put the new pump on as compared to the old one before. I always discounted the pump being bad because i had a new one on it but in hindsight it makes sense it was a fuel flow issue. He did have a Link handheld deal that would hook into the computer but a connection must be bad somewhere because it never kicked on, we didnt mess with that anymore after he determined it was a fuel issue.

[Ace2cool]

To be fair, I trust Walbro a LOT more than MSD.