I realize there isn't much traffic these days, but there are a few of us still checking in and almost anyone will have more knowledge than I, do mechanically speaking.

I have a Greddy kit on a built block done by Dynosty wayyyy back when it was still Injected Performance. Finances are much tighter these days, hence my installing a twin disc clutch myself. It was a challenge for me when installing to get everything out of the way when trans was going back in, especially pesky vacuum lines. Shoulda taken a few minutes to zip tie more than I did.

Car changed night and day with response upon accelerating better than when first built!

Didn't really drive the $hit outta it at first so not 100% sure the clutch install messed anything up but now, there is a shuddering/hesitation going on as boost builds.

I'm trying to do a boost leak test first. On the greddy kit can I just take both filters off and pressurize the system from one side while blocking off other? Should I also block off the 3 vacuum lines at the rear of the Cosworth manifold? What about the larger hose coming of the intake pipe before TB?

I only boost to 14 lbs if I rem correctly. So should I max out at that pressure?

Any suggestions on things to trouble shoot? I was thinking sending injectors out next.

Thanks

 

If your vacuum lines are older than 5 years change them out, all of them. If the plugs have over 50k, same. Check/remove/replace the air cleaner element. If you are running old fuel or ethanol added, run a bottle of Techron or BG through the tank. Gl!

 

Have you data logged your MAP, AFR, and timing first. I would check to see if the hesitation shows up in the data first.

 

Data WHAT?!?! kidding

Thanks for suggestion guys

 

I had a hesitation under boost issue I was chasing after my build as well. If it's a weird stutter/hesitation, it could be coil packs or plugs. Mine ended up being a bad set of (brand new) coil packs from a well known brand. I chased my tail for days until I decided to swap in the 20yr old coil packs I still had in a box and it ran like a scalded dog!

Eventually I put in a set of R35 coil packs from Concept Z and it's been great ever since.

 

added to the list RENFRO!!

 

Regarding BLT......I tried it without the vac lines plugged and all I could hear was air rushing into coswroth plenum.

Pinched them and I hear a fricking gurgling noise from somewhere in the back half of the engine?!?

Tightened vac hose leading to fuel pressure regulator (I think that is it's function) thinking it might be fuel but no change.

any guesses what that could be?

 

double post

 

Just seeing this … late to the party (as usual) …

Is the hesitation / shuttering consistent at a certain RPM and boost? Or is it inconsistent?

I would remove all the vac lines and what JHC said, just replace them - too inexpensive to give it more than 3minutes of brain energy. I’ve gone to aluminum hoses with AN fittings myself(as best as I can) to prevent this. And plug the barb fittings on the plenum in an effort to eliminate as many variables as possible.

The larger hose is your PCV valve / hose setup? You could remove it and plug it for testing but I can’t see this being an issue … could be?? I suspect it’s between the MAF and the TB?? Are you still running a MAF sensor? Or did you eliminate it and add a GM temp sensor?

I would set your compressor to 15 to 20psi but wouldnt go too much higher.

Are you getting any check-engine-lights?

Everything that previous ^^^ poster ^^^ have mentioned all have value … to further the check list…

check your grounds … Make sure the grounds are tightly secured and then inspect the wiring. It took me a little while to figure this out but I will unplug a coil pack, clip on to the ground pin(receptacle) with one lead and then the ground/engine with the other lead and shake the harness and ensure you have continuity on the line. Sometimes the harness will test fine when the car isnt running but vibrations/bumps/movements will cause a ground disconnect.

I’d do this for the coils/spark plugs, your cam shaft & crank shaft position sensors, throttle body, MAF sensor,

Do you know anyone who has an extra set of OEM coil packs that you can borrow or buy? I’d swap in a donor set and see how it does.

If you want me to run your injectors through my injector cleaner let me know - just cover shipping.

What fuel rails are you running? I think the VQ is subject to fuel pulses that ‘might’ cause this?? I’m not sure if it would be directly applicable to your case -

Have you checked your plugs? What are your plugs gapped at? I think spec is .044” and FI guys are dropping down to .03” - could this be spark blow out?
I would also inspect the porcelain of the plugs - ensure you have no cracks. Maybe get a inexpensive set of replacement plugs and drop them in.

With that being said, disassemble the coil pack and make sure the spring in the stem of the coil pack looks good. Also inspect the wiring to the coil packs.

Grey Z brought up a good point about datalogging … I would probably do this first bc this could be a tune issue.

 

GREAT!!
That list will hold me for a bit.

New NGK Iradium plugs one step colder on order.

Vac lines and grounds will be next.

I will prob make the jump to the GTR coils next.

Yeah still MAF sensor. I'll have to check the fuel rails since it's been about 13 years since the build.

I've reached out to Jon at Z1 to see about a visit there if I get done with the list and have not heard anything in a couple days.

Thanks for the help guys!!

 

Give Z1 a ring if you're trying to get some dyno time scheduled. They've expanded a ton and have a lot of new processes for things. I'll be out there May 12th for a retune.

 

Yup....been by once to pickup a radiator support bracket and they ship incredibly fast!

be nice if they were near that speedy replying to inquires. Bet Jon is a busy man tho.

 

Yea - good idea and make sure they are gapped correctly - I like them around the .03” mark for your boost levels

Dont do this … just stick with OEM … whatever came in your car. I would buy used Nissan OEM before I bought new aftermarket

it would be unwise to introduce another variable into your problem

have you cleaned your MAF sensor recently?

Not likely it’s your fuel rails but I’ve heard of this issue before from the HPA guy.

And do you have any check engine lights on?

 

No check engine lights

I have not cleaned the maf but will!

On the gurgling noise during BLT I've read about oil being forced thru the oil return off the turbos if seals are warn. Hope that's not it but have lots to address before that.

Thanks for insights James!!

 

Capped off rear vacuum ports and tried one last BLT before tearing into it.

Still lots of burbling/gurgling BUT slight hissing and fuel smell at driver's side front. Figured it was a leaking injector.

Took plenum off and noticed a gasket in between spacer and block. Now I'm concerned there could be a leak in gasket. It's on there VERY well. Was thinking of trying to saturate gasket with acetone in attempt to remove. Thinking I might throw plugs, clean injectors, and maybe OEM coilpacks before tearing up gasket and perhaps spacer.

 

The 350Z intake hisses normally. You sure that's not the sound you're hearing? Is the sound louder near the air filter?

 

I ain't sure of $hit......that I know.

After pulling the cosworth plenum off, I found a line (larger than vacuum line off rear) running out the bottom rear that I had not clamped off or plugged. Perhaps that was the source of air into liquid noises?!?!

Attempting to research plenum gaskets and proper sealants now as that seems like a possible source of issues. I use a lot of Permatex aviation on an older engine from the 70's I'm working on and it seems like it couldn't hurt between the gasket that is glued to bottom of plenum but has none to top of spacer.

 

Remove the paper gaskets and replace them with two OEM metal gaskets. The cheap paper gaskets that come with the spacers are notorious for leaks.

 

would you use the Permatex on them?

Thanks for the suggestion!!

 

You could, but it's messy. The OEM gaskets work.