Car bogs on throttle blip
 

Engine is rebuilt S5 engine with FD rotors and housings, with S4 intake manifolds and throttle body. The engine literally just got put in, and has 0 miles on it. Running on an Microtec LT8 with 750x4 injectors and BNR Stage 2 S4 turbo. I have looked extensively for vacuum leaks, and fixed the one I did have which was at the secondary injectors; I do not appear to have any more vacuum leaks.

There are a few issues I am experiencing.

1. Idle is higher than it was before replacing the engine (didn't touch idle screw at all on throttle body).
2. Idle hunts around.
3. AFRs go between 11 and 12

The BIGGEST ISSUE
4.. When getting on the gas, it bogs and wants to die (or does die please see video). If I get on the throttle very smoothly, it will rev up, but if I blip it at all in a more normal matter, it will want to die. You can see in the video that when I blip it and it goes to 10inHg, it will try to die.

I have calibrated the TPS in the microtec software, issue still happens. The TPS is S4. If there is any info needed that could help in diagnostics of this issue, I will be more than happy to provide.

Any help or advice would be greatly appreciated, thank you! :)

sounds like a fuel issue, be sure the fuel lines didn't get reversed. it is possible for an engine to still idle and somewhat rev with them reversed.

line off the fuel filter> primary short rail.
the firewall connection> line off FPR at the end of the long secondary rail

Thanks Ben, we will be checking that out, and slapping a fuel pressure gauge on it too.

For reference, what do you set the static timing at? The new engine has a racing beat pulley on it so we stabbed it at 0 degrees. Not sure if we are off by 5 or not compared to what you had it stabbed at originally.

Looks like a load map issue. Also, when you started the car it when from lean to rich... This is a no no for rotaries especially if the motor is ported. You might want to fatten up you crank setting, after start enrichment then the load map (10" to 5" to 0")

i usually set idle timing at about 18* at idle, unless you need it to pass emissions then i would set it at 0 with the standard 15* split, this is software based and doesn't have anything to do with adjusting the CAS.

on the RB pulley from left to right when standing at the front of the car is: -10/0/10BTDC/20BTDC

lock the timing in the microtech hand controller then set the CAS to read -5 off the front rotor lead wire(between the 2 left marks on the RB pulley), this will set the timing to where the engine was tuned to run at as it was set based off a standard FC pulley. the trailing will hit off to the left of all the marks.

Thanks for the input :)

We checked the maps and they are fine. It's still running the tune it had with the prior engine; in which even with a cracked rear iron spitting out all the oil, it still ran and idled fine on that engine lol. Nothing is different other than I slapped in a rebuilt engine. EFI setup and everything is exactly the same.

Thanks Ben this is exactly what I thought, we will go ahead and re-stab it and go from there. Due to school and jobs we haven't had anytime this week to go further along with the diagnosis. Will probably have some more information by Friday or Saturday.

If timing is correct and everyting else is ok. It could be a pump throttle issues. Was the old engine ported? What do you mean by new EFI setup? All these variables make a difference.

To answer your questions:

1. Old engine was ported, new engine is not.

2. The EFI setup is exactly the same between the old and new engine: Nothing was changed out.

i thought the old engine was an original Jspec S5? either way porting wouldn't cause a complete cut out like you're experiencing which sounds like extreme fuel starvation. it may be idling with ok AFRs but it is going full lean on the throttle.

the car should still be in matrix mode, so if the fuel pump and fuel line routing is not the problem then my next best guess would be somehow the low RPM fuelling maps were bumped somehow. the affected maps should be idle/1k-2k. there shouldn't be any numbers dramatically out of place.

Ahh sorry this is for my white car (Jaime Austria's old car, I bought it off him almost right after he got it back from you). I believe when you built the engine you had ported it. Which means I have a practically new-rebuilt ported engine sitting on the garage floor with a cracked rear iron; was thinking I can get away with just replacing the rear iron on that one and have it as a backup lol.

Hey all,

I came across this exact issue when tuning my S5 engine. It would only rev when given very little throttle, otherwise it bogged or died instantly. Pump settings ended up being the culprit as I recall (more than a year ago at this point). It doesn't make a whole lot of sense, but she revs nice and easy now.

My setup is completely different than yours but if rx72c can't provide some insight no one can!

Best of luck!

ah ok, yes it's been a while but i'm fairly sure the engine was ported. i did not retune it as it needed to be broken in so the tune on that ecu should be rechecked since it has been loaded in there for about 4 years now and the last engine cracked a seal. so break in the new engine but be sure that it is rechecked before pushing the new engine, pretty sure i explained it to jaime when sending it back to him.

it has the "unbreakable" seals so assuming the corner seals are ok then the rear iron could probably just be replaced.

the issue you're having still seems to be unrelated to porting though, i would recommend checking fuel pressure which could be related to the failures. the pump was working fine when it left but you might now be seeing the initial cause of failure versus an intermittent problem that it may have started out as.

Thank you for the input, I will check that out.

Cool thanks for the info.

So the fuel pressure was checked, and at idle it is 60psi with or without vacuum applied to the regulator (stock unit). Not sure if the issue is being caused by that abnormally high fuel pressure, but I am going to change the fuel pressure regulator out tonight and see what happens.

I will report back.

60 is higher than i would expect, even the walbro with a stock regulator should only idle around 50psi so it may be pointing to some problem in the system. the regulator did fail on it once already but only in a way that the diaphragm ripped and would push fuel into the rear intake runner.

Ok problems solved.

First we restabbed the CAS as we originally stabbed it 5 degrees off. This fixed the erratic idle issue.

I then found that when my buddy put the injector clips on, he swapped the primaries and secondaries :facepalm: I guess thats the problem when working with multiple people on these types of projects lol. This fixed the bogging on light throttle issue.

So car runs perfectly fine now and is back on the road to get broken in.

Thanks everyone for the input and help. Issue resolved.