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Tonyr33gtst

Help please, RB25DET runs better on 1/2 throttle!

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Hi All,

I have a R33 GTST and since I have owned it it has had an issue. It is standard apart from a FMIC and a few internal gauges and silicon pipes.  If I accelerate full throttle it is slow, no obvious misfiring, funny noises, just slow. I have fitted new plugs and after only 10km they are all very white! So think its going super lean! All the same colour. It appears to have a reasonably new fuel filter in it and the plugs I removed before I fitted a new set were also not that old looking.

 If I use half throttle at around 3-5psi all is well and the car goes well. I have noticed that the internal after market boost gauge hits 14-15psi when accelerating full throttle which seems too high. I have plumbed the actuator to run directly off the intake pipe of the fmic but still it boosts at around 14psi! How come it boosts so high? Is that my issue? No sign of a bleed valve and no boost controller. Should just be running actuator pressure so cant understand the high boost?

The car revs, drives fault free and does not smoke whatsoever.

Any help will be greatly received.

Thanks

Tony

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The too much boost will be the problem. Ecu is going into r and r and cutting your fun to protect the engine. You need to work out why it's overboosting. Try to keep boost to 10psi and lower to keep the stock ecu happy.

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Thanks admS15, What exactly is R and R, what does the ecu do at that point? I guess it stands for rest and recuperation but no idea what the ecu does, timing?fuel? so why so lean plugs if the ecu is doing its job? I have seen this written before but couldn't find out what that meant exactly and yes I think it may be that the boost is too high for the ecu to deal with so I am glad you thought that too.

I did also consider fuel pressure as when i remove the vacuum line from the FPR it made no noticeable difference to the idle. I  just don't have the understanding to fathom out what can be making my turbo boost so high, the actuator moves freely when moved by hand and the rod moves in and out too.

What can I look for, what causes too much boost? If there was a leak in the piping to the fmic would that cause it? If the gauge shows 14psi then surely the actuator is seeing it too? 

 

Edited by Tonyr33gtst

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Rich (fuel mixture) and retard (timing), stock ECU is doing this to protect the motor in an overboost situation. Although I do like your version more lol I'm picturing my motor on a beach somewhere with a martini after a hard track day :)

Has the car done this ever since you owned it? 

Removing the vacuum line to your FPR at idle won't do anything, that vacuum line is there to increase the fuel pressure as the boost pressure rises. 

I'd be looking around for a sneaky little boost t style boost controller hiding in your engine bay that is spoiling your fun. Maybe grab a workshop manual and make sure all the vacuum lines are going where they should be.

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Watch the boost gauge as you accelerate for a clue as to whether its going into R&R.  Although the white plugs make me think you might have a fuel problem e.g. pump on the way out.

As above check your vacuum lines going to the actuator. Is your boost solenoid still connected or has it been by-passed? Try connecting the vacuum line directly from its source to the actuator.

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I'm with Kiwi. Lean as f**k, caused by low fuel pressure. Solve that first, then check to make sure that the boost gauge is not telling you lies. What is the stock gauge going up to?

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Thanks Murray, Kiwi and GTSBoy. 

I have already plumbed the actuator direct to the inlet boost pipe from the fmic as in the picture to make sure no more than actuator pressure and that made no difference, hard to see in pic but that feed goes from boost pipe straight down to the actuator. Car has always done it since I bought it so I don't drive it, didnt notice it as it was fine at low to medium throttle and didn't floor it until I got near home. 

What clue would the boost gauge show me Kiwi as it dosent drop back down on boost to a lower level it is only when I back off the throttle  the boost goes down.

And that ecu sure dosent look like it's making the car rich to me to slow it down. Surely the plugs would not be white after a quick boot up the road to test it but more black from the R&R the ecu is meant to be doing?

And GTS Boy the stock gauge does not go right up when my boost gauge shows 14psi which I thought odd. 

Is my actuator faulty as should actuator pressure be std must be 7psi odd and boost solenoid make up To 10? 

What should I check next? maybe change the fpr or take the fuel pump out and inspect? To me it's more likely fuel starvation but maybe r&R. What else is there to check fuel wise other than pump and fpr? There is a sensor on the fuel rail, what does that do? Any ideas would be great thanks lads.

 

20200406_160402.jpg

Edited by Tonyr33gtst

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7 on the stock gauge is a little less than 14 psi. The stock gauge isn't bad, so if they disagree, suspect your aftermarket one first. Add another gauge in temporarily (from a workshop) to double triple check,

The behaviour of the boost gauge (staying up) sounds sus too. Double and triple check the lines feeding that, just in case of stupidity.

And RB25 stock actuator pressure is 5 psi. It is brought up to 7 psi by the stock boost control valve.

What to check next? Put a pressure gauge into the fuel line upstream of the fuel rail and load the engine. If you have to go to a workshop to do this, then do it. There is no point flailing around in the dark. Do not f**k about with the regulator. There will be nothing wrong with it.

There is no sensor on the fuel rail. It is a pressure pulsation dampener.

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Thanks GTSBoy, I just tried it again after managing to move my actuator a little  (ie a couple of mm towards the turbo) in its mounts which now seems that it spikes at 13-14psi and falls to 10-12 so 1 psi or so a bit less maybe. The std gauge on the dash boost to very near the +7 top at about 6.5-7 peak. Does this mean near 14psi on that scale? It seems to restore power when i drop to around 5 psi.

As my boost/vacuum pipe is direct from the intake to the actuator surely I should only see 5psi without any interference from a solenoid, so what would that look like on the in car boost gauge? also where does peak boost sit at 7 psi? I suspect the actuator is causing over boost. Fuel is a concern but need to make std boost first to see how the fuelling goes at 5-7psi. 

I have a afrp on another car I have that has 1 to 1 ratio and base pressure at 50 psi, if i put that in the return line after the factory frp could i check it that way to see if its a fuel pressure issue? I dont know if i can do that with the std on infront of it but i guess it works by restriction so as the afpr has a higher pressur/more restriction it may still work???

However, I don't know how I will see under load unless i can film it!

By upstream do you mean after the rail on the return?

 

Thanks for your help.

Edited by Tonyr33gtst

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17 hours ago, KiwiRS4T said:

Watch the boost gauge as you accelerate for a clue as to whether its going into R&R.  Although the white plugs make me think you might have a fuel problem e.g. pump on the way out.

As above check your vacuum lines going to the actuator. Is your boost solenoid still connected or has it been by-passed? Try connecting the vacuum line directly from its source to the actuator.

I have disconnected the factory boost solenoid so I can run at basic actuator pressure so the ecu will not have any control of that, but it didn't seem to effect the boost when it was connected in the way that you might be talking about either. So if R&R if that was coming into play would it lower boost? It retards ignition so does that reduce boost? as the boost has never dropped, the car just goes slower, drop back to 5 psi and its off again. at 10+psi it has the feel of a N/A car. so no boost noticeable.

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8 minutes ago, Tonyr33gtst said:

+7 top at about 6.5-7 peak. Does this mean near 14psi on that scale?

1 bar is 14.5 psi is 760 mm of mercury. The stock gauge is marked in hundreds of mm of mercury. So the 7 is 700/760 of a bar, which is 0.92 bar or 13.3 psi.

 

10 minutes ago, Tonyr33gtst said:

As my boost/vacuum pipe is direct from the intake to the actuator surely I should only see 5psi

True. But your wastegate and/or actuator could be stuffed/sticky and not opening properly, hence giving you big boost until the exhaust manifold pressure rises into stupidland and blows it open a bit more, leading to spike then drop.

11 minutes ago, Tonyr33gtst said:

Fuel is a concern but need to make std boost first to see how the fuelling goes at 5-7psi. 

No, fuel is your first concern. Overboosting while it is lean as shit will KILL your engine. You have to stop doing it until you have diagnosed the lean issue.

12 minutes ago, Tonyr33gtst said:

I have a afrp on another car I have that has 1 to 1 ratio and base pressure at 50 psi, if i put that in the return line after the factory frp could i check it that way to see if its a fuel pressure issue?

No. Put a gauge on it. Don't f**k about with crazy secondhand ways of trying to work out what the fuel pressure situation is. Do it properly, measure it directly.

Another regulator will not magically make a failing fuel pump work any better anyway!!

13 minutes ago, Tonyr33gtst said:

However, I don't know how I will see under load unless i can film it!

Fuel pressure gauge gets teed into the fuel line, and you run it out of the bonnet and hold it in your hand/lap/passenger's hand/lap as you drive. If the pressure starts high and plummets on load, you know what's happening.

Even better, do it on a dyno.

14 minutes ago, Tonyr33gtst said:

By upstream do you mean after the rail on the return?

Upstream means up stream, meaning in the direction from which the flow is coming. The fuel pressure is set by the regulator at the outlet of the rail. You can only measure the rail pressure at a position upstream of the reg, which means at the inlet end.

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40 minutes ago, GTSBoy said:

Thanks, re the actuator, That's what I said, Actuator could be faulty as should not be boosting to 14 psi on actuator, yes it may be the turbo wastegate but will replace actuator first rather than turbo as only a few bucks and a 10 minute job.

Don't you think that the Fuel may be lean as boost so high and no map for it!?  You cant normally run double the boost without a map can you without going stupid lean or does the std ecu compensate to this type of boost fairly well? I need to address the boost to get it to 5-7psi then see if still lean imo. Its lock down here so no way to get to a dyno but like your idea if a t and a gauge out of the bonnet. I will do that as i have a gauge that will work. And ill put it upstream. What should i see under boost for fuel. std is 3 bar I think?

Lastly so from what you are saying a normal gtst should show a boost on the cars gauge of 2.65-3.7 at max boost ie 5-7psi? So nearly hitting 7 is way over what the std actuator should be giving!

 

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I have opened up the fuel tank and it appears to have a nearly new Walbro GSS341 255 fuel pump in it! It appears to be a genuine one. With decent writing on and not like a fake The plot thickens! There is a bit of discolouration/darker bit of the filter near the pump inlet but not much. I will try and clean it and see if anything comes out but it all looks almost new there. When I bought this car it was meant to have a G4 ECU it hasn't but just had a look and it has a sticker on it from a tuning company but it is not a G4, no usb etc and appears to be a standard one when i open it up, maybe it has a tune on it, see photo? Tried calling them but no response.

 

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ECU does say Stage 1 V2 on it but i'm not sure if thats right. If so could this be the reason it is boosting high if on Actuator?? It has no way of bleeding boost from the actuator does it if the solenoid it out of the loop?

Just looked at fuel filter and it is 2 years old Mahle one so doubt its that either. I spoke to the ecu guy and he suggested to check the base timing. Any ideas what this should be?

Edited by Tonyr33gtst

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He said that if too retarded it could cause this issue. Its an auto so should it be 15 or 20 degrees as ive seen both mentioned. Thoughts?

 

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Edited by Tonyr33gtst

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This is getting out of hand. 

Put a pressure gauge in your fuel line, after the fuel filter but before the rail. If you are set on not going to a workshop or dyno, you can get something like this - 

https://www.prospeedracing.com.au/AEM-X-Series-Digital-150-PSI/10-BAR-Oil-Pressure-Gauge-30-0307

Once you've diagnosed this current issue, you could use it for an oil pressure gauge which is always nice to have. If you ever get a proper ECU, you can feed the signal to that instead and use it for things like engine protection etc. It is money well spent. 

Stop trying to diagnose this lean condition using other methods, you've already been told numerous times you need to know what the fuel pressure actually is. Simply looking at the fuel pump won't tell you anything. Believe it of not, Walbro pumps can fail too. 

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2 hours ago, Murray_Calavera said:

This is getting out of hand. 

Put a pressure gauge in your fuel line, after the fuel filter but before the rail. If you are set on not going to a workshop or dyno, you can get something like this - 

https://www.prospeedracing.com.au/AEM-X-Series-Digital-150-PSI/10-BAR-Oil-Pressure-Gauge-30-0307

Once you've diagnosed this current issue, you could use it for an oil pressure gauge which is always nice to have. If you ever get a proper ECU, you can feed the signal to that instead and use it for things like engine protection etc. It is money well spent. 

Stop trying to diagnose this lean condition using other methods, you've already been told numerous times you need to know what the fuel pressure actually is. Simply looking at the fuel pump won't tell you anything. Believe it of not, Walbro pumps can fail too. 

Er I would suggest that you dont comment if you are not answering my question. I will not be spending $400+ on a gauge I have 2 oil pressure gauges in other cars and this skyline has one too that I could use come to think of it to check fuel pressure I have already said I will try that too.

 

I am not SET on not going to a dyno! We are in lock down in our country so obviously I cant take to a dyno! I also have a AEM wideband in another car that I could fit to see if lean I guess. I'm very surprised you are not in lock down also wherever you are and able to go to dyno's etc. We are not allowed out only to buy food and medicine here.

My question was asking about timing as that is what the ecu programmer suggested as he said in his opinion it wont be fuel pressure. Running too retarded would cause too hot running, high boost and poor performance hence white plugs. I might as well give that some thought before I mess around with plumbing in fuel pressure gauges which incidentally no one has answered above when I asked what fuel pressure it should show at 14psi boost.

Edited by Tonyr33gtst

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I am commenting because I am genuinely trying to help you. 

There is a cost involved in this matter, dyno time, workshop time or any other parts required to diagnose or repair. 

It was my opinion that $400 is money well spent and the gauge/sensor have multiple purposes to diagnose this issue then add value in other areas later. 

The skyline does not have a useful oil pressure gauge from factory, it is basically a low oil pressure dash light. I can show you 40+ psi swings in oil pressure and no changes on the factory 'oil pressure gauge' if you like.

I am in nsw Australia. Workshops here are still open and people are able to take their cars in for repair. I don't know what your circumstances are so cannot comment on that. 

Fuel pressure at 14psi of boost should be around 58psi give or take (provided your using the stock FPR etc)

It looks like your on the stock ecu, if you had an issue with the timing I would expect that issue to be everywhere. Not purely at WOT on high boost.

YouTube anti lag, that is massive fuel and retarded timing. I doubt your car is doing that. 

Seeing as you have a wideband gauge, why don't you hook it up and see what the mixtures actually are?

I am also amazed that your tuner has said he doubts this is a fuel pressure issue. I would look for a new tuner but that's a matter for yourself.

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2 hours ago, Tonyr33gtst said:

 

 

 

My question was asking about timing as that is what the ecu programmer suggested as he said in his opinion it wont be fuel pressure. Running too retarded would cause too hot running, high boost and poor performance hence white plugs. I might as well give that some thought before I mess around with plumbing in fuel pressure gauges which incidentally no one has answered above when I asked what fuel pressure it should show at 14psi boost.

Keep your hair on mate! Clearly I have too much time on my hands and I have had a look at the workshop manual (you should search on-line and download one for yourself) regarding fuel pressure.

 Although people commonly  use a number between 36 and 44psi as a starting point the manual says:

at idle 35.5psi (or with vacuum line removed 42.3 psi) and this number should rise lb for lb with boost.

The workshop manual says timing should be 15 degrees (it doesn't say anything about autos being different). On many RBs there is a sticker under the bonnet with this information - although it may have peeled off or been painted over.

As your car is stock my guess is that you do not have a tunable ecu but that some one has put a "miracle chip" ("buy this chip and your car will outdrag corvettes" kind of thing in the stock ecu.

In your first post you say that you suspect that your engine is running lean and almost everyone else has agreed that this is very likely. Since you don't have access to a wideband you should at least check the fuel pressure and you say you have a suitable gauge...so do it!

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