Leeroy_25

I have a bit of a boost spiking/creep problem. Having not long had the car on the road I have only just fitted a new clutch that doesn't slip and been able to drive it properly!

I noticed today having finally got on some open road the the spike/creep only appears to occur when accelerating from low speed in a high gear then once the revs get up it drops back.. The charactristics are as follows.. Accelerate hard in low gear away from the lights and up through the gears no problem boost holds steady around 10psi or just under..
Pull out to overtake while cruising at low speed in high gear (say 40mph in 4th or 30mph in 3rd) rpms are around 2k.. as the rpm rises to around 2500rpm boost comes in to around 10psi. past this point the sound of leaking air (hissing) can be heard and the boost keeps rising to around 15psi (seems to be worse the slower the rpm is rising) then at around 3500rpm (which I think it where the second turbo comes in?) air leak sound stops and boost drops back to 5psi suddenly then rising again with the rpm back to 10psi by about 4000rpm max and holds steady?
Then as far as I have been abe to tell so far all is fine..

Sounds like maybe the problem is confined to the first turbo? but then I don't understand why the problem seems okay when the second unit kicks in?
The second unit is working but fine but leaking oil. not enough to cause smoke through the exhaust but it is going through the turbo and coming back out the recirc valve. But that is the rear turbo??

Help please. Any ideas of what I should look for?

Thank you
Lee

Retserof

iTrader: (1)

Is your car stock? First, it sounds like there is a boost leak. Have you checked the ductwork and clamps from the turbos to the intercooler and from the intercooler to the throttlebody for leaks, splits and loose bits?

As for the spike, here is a chart that shows the "normal" or stock boost curve (black line), the overboost fuel cut curve (red line), and my car's boost pattern (blue line) prior to some modifications. If you were to plot your car's boost pattern, would it resemble the stock boost curve?

Leeroy_25

Thanks for that..

The car is stock accept for a large mushroom intake filter and back box.

I can safely say my peak boost between 2500-4500rpm is much high than stock! The rest of the graph would be fairly accurate. I think the boost probably settles just under 10psi though.. Nothing to say how good my guage is though.. it's not an expensive one. But according to the guage it maxes around 15psi! How do I know if the fuel cut is working?? I am not really too familar with the setup of the rotary! I have had a look around vac pipes and stuff and couldn't see anything.. The other place I could think I may have a leak is the LIM gasket.. Someone asked if I could smell petrol when I drive it hard.. and I can.. Would I be correct to think thats a symptom of a failed LIM gasket?

Cheers
Lee

Seanybaby2

i would look into the gasket and maybe even check your intake filter or back box usually that kind of thing does not happen to a stock rx7

MOBEONER

iTrader: (18)

it might be a bad solenoid.

DaveW

http://www.autosportracetech.com/RX-...leshooting.htm

drga55

Check your wastegate actuator. It sounds like the diaghram in the actuator might be broken.

Retserof

iTrader: (1)

The low restriction intake and back box can let the boost pressure build faster and higher than stock. 15 psi on stock turbos is plausible, but it could be that your boost gauge reads a little high too. The fuel cut is a last ditch defense against operator-caused engine damage, if you're lucky.

When overboost fuel cut is triggered, you'll know it as the effect is dramatic because it happens at high rpm and heavy load -- it's as if your passenger suddenly reached over and turned the ignition off and on again. But it is not the ignition that is interrupted, its the fuel supply. This is very hard on the engine and potentially destructive in itself. Boost cut is more likely to occur in cold ambient air temperatures. Avoid it -- don't tempt fate.

If all the vacuum lines are OK and the solenoids work, and nothing else is wrong, you need to limit boost with a controller of some kind or by increasing the orifice size in the turbo control line restrictor pill. Search the forum for more info.

Any leak in the plumbing between the turbo compressor outlets and the engine will give a whistling or wooshing sound. Besides a possible LIM gasket leak, have you tightened up the hose clamps on the duct connections?

Leeroy_25

Thanks for all the info guy's. I will have to have another look at some of the piping and clamps on the diagram that was linked above.. I find it strange that I appear to have a boost leak but am also getting a massive boost spike?! Surely that means the turbo must be making even more boost than the gueage is reading? I am hoping to go single turbo in the new year so then I can dump al the crap and fix the LIM gasket and hopefully that will solve all my issues?!

Resterof: You mention running a boost controller.. I have one but its' not all hooked up.. Is this not a bit of a mare to rig up on the stock units? SHould it control the boost better than the factory setup?

Cheers
Lee

Retserof

iTrader: (1)

Sorry, I can't offer much help on boost controllers. I don't have one. Since my only mods are a Pettit downpipe and a Racing Beat cat-back, I didn't need much compensation to get the boost pattern back within safe limits.

I just removed the stock restrictor pill (which is supposed to have an opening of 0.062” or 0.064") from the wastegate actuator hose and replaced it with a Holley carb jet, with a larger opening. It is trial and error to find how much larger the pill opening has to be in order to lower the spike and get back to a 10-8-10 boost pattern that was normal for a '94. Later cars apparently had a 10-8-8 boost pattern. Now I have a 0.0755" carb jet installed and the boost pattern is 11-9-10. When I get the time to work on the car again I plan to go to a larger pill still so that I have that 10-8-10 pattern in cold winter weather. A mechanical or electronic boost controller simply allows you to dial in the effective opening instead of screwing around with changing pills.

It certainly is possible to have excessive boost and a boost leak at the same time. Try this test: Briefly accellerate the engine to WOT in neutral, (From idle, punch the gas [WOT], get the RPMs above 5,000 but less than redline). About +4 psi should be obtained as you pass from 3,000 to 4,000 RPM. If you do not get this you most likely have a leak of the boosted air and you need to do some troubleshooting.

Mahjik

iTrader: (1)

In most cases, an aftermarket electronic boost controller (EBC) will be able to control boost spiking. When I say "in most cases" as the controllers typically need some "tuning" to get them right. In that sense, it will only be as good as you make it. However yes, aftermarket EBC's are better (i.e. respond quicker) than the stock control system.

Leeroy_25

Thanks again..
I'll try the boost leak check when I use the car next.. (Next weekend now!!) as for te pill you mention.. where exactly is this fitted and what does it look like? I presume it's what lets the vacuum operate the actuator from the size you changed it to.. Would it be possible any oil or muck hindering air flow here could cause a problem?
I have just been out in the car and the problem is certainly not consistent! One minute I seem to get a perfect boost response in any gear through the rev range.. the next I am getting 1 bar spikes and it seems to be above 4500rpm as well as below. I tightened all the hoses and had a look where I could for damaged ones and can still here the leak. I am wondering if it is actually air coming into the boost guage tat I can hear as it sounds like it could be in the car! I might try and take out the boost guage and blank the hose off for a run and see what happens then.

I think best bet is hurry up saving for the single conversion!

Lee

Retserof

iTrader: (1)

The restrictor pills are in the pressure hoses running from a double nipple fitting on the primary turbo outlet to the wastegate and precontrol actuators. Check the pills to may sure that they have not plugged up with crud. If your car is a 94 or later model year, the restrictions may be built into the inside diameter of the hose nipples rather than as pills inside the hoses. If so, you would have to drill them out to larger diameter. However, mine is a 94 and it had the pills in the pressure lines. They were perfectly clean. The pill in the wastegate actuator hose is the one that folks normally change out for larger orifice pills to limit boost after making intake or exhause modifications.

Because your boost spike and leak noise problems are not consistent, something else must be going on that requires a deeper level of troubleshooting.