spike.spiegel

I searched and browsed the autosportracetech site as well as this forum, but didn't find anything specific to my symptoms. I have a stock setup, and am getting 14psi spike on the primary turbo. After spiking, it goes back to 8psi on transition, then slowly up to 10psi at redline. I noticed it's only doing this when I slam the throttle as fast as possible. If I am gradual with the throttle and take .5 seconds to push down the throttle, I get a good 10-8-10 pattern. I know a lot of people will recommend a boost controller (or larger pills), but it doesn't seem right that I should have to resort to that when I am still stock. Any thoughts at all are greatly appreciated. Thanks!

FDjunkie

You might be experiencing the beginnings of a failing Pre-Control Solenoid. When mine failed it quickly became vary slow to operate resulting in significant changes in boost behavior, particularly at transition.

books

iTrader: (8)

Before I replaced the precat with a downpipe on my last FD. It was spiking to 14 psi on the primary then dipping to 8 at transition but never hit 10 psi after transition. It was closer to 9 psi after transition. With the downpipe the issue was resolved.

Kento

How long have you owned the car? Are you sure this is something that has just started occurring, or something that you just noticed? The reason I ask this is that much of Tucson, AZ, is at elevation. Due to the thinner air, your turbos are working harder (spinning faster) to produce the same amount of boost; "slamming the throttle" open with the turbos already spooled up suddenly releases a major pressure wave into the intake. The wastegate may not be ready to handle that sudden increase in boost that is already higher to begin with. It also causes slightly higher pressure spikes during transition.

spike.spiegel

Thanks for the responses guys. Kento, I just bought the car and installed the boost gauge so this is the first time I've ever been able to monitor the boost level. So it could definitely be related to elevation/temperature/humidity. I still feel like 14psi is a lot though, I'd be more comfortable if it was 11-12. I think books could be right, I could have a clogged precat. Guess its time to go for a downpipe/ecu? In the meantime, I'll just be a little more gentle with the throttle.

Kento

If you had a clogged pre-cat, you wouldn't be able to build boost quick enough to spike. Spiking/creeping is caused by increased flow, not less.

spike.spiegel

Well, I think something is not functioning properly if I'm seeing these boost levels. What else could it be? Is the only possibility pre-control actuator? How much of a pain is it to repair/replace that?

books

iTrader: (8)

I agree with Kento's logic. You ought to replace the precat anyway. Here is a good site for troubleshooting turbos; http://www.autosportracetech.com/RX-7/rx7stuff.htm

this is what it says about a high boost spike: "· If boost pressure is way above 10 psi, (i.e. spiking at >14 psi) then the tube between the Primary Turbo Compressor and the Wastegate Actuator has popped off. Do NOT simply plug the popped off hose back on as it will pop off again. always use a new small hose clamp or a nylon zip-tie / ty-wrap for these hoses."

spike.spiegel

Yea, I read that, but those hoses were on there really good. So I didn't know what else to check. I'll definitely be getting a dp in the near future, just not sure if that will solve my problem...Guess I'll find out

Retserof

iTrader: (1)

Don't be surprised if the problem gets worse when you replace the precat with a downpipe. I have a 94 base (original owner). Stock boost would rise to 12 or 14 before transition at 4,500, then drop to 9 or 10, and then climb back to 11 or 12.

After the downpipe install, boost comes on quicker and is up to 2 lbs higher all the way, and on a cold day I hit the overboost cut at about 6,000 rpm -- very nasty. Like you, I have been trying to figure out why. (My boost gauge itself is OK according to a Mityvac, and all the hoses are good.)

Kento

I guess everyone's forgotten my original post in this thread. It doesn't take much elevation to cause the FD's stock (relative) boost to rise significantly. I've seen my boost rise by 2-3 psi overall (including a much higher spike to 14 psi at the transition) at just 2000 ft. above sea level. In fact, I did eventually hit the fuel cut at 6000 rpm.

Retserof

iTrader: (1)

I'm confused -- I thought that you get higher boost levels with denser atmosphere, as in cold winter air. If so, wouldn't the thinner air at elevation actually result in lower boost levels? I've never driven my car above 1,000 feet.

BigIslandSevens

iTrader: (4)

check the nipples on the pre-control and wastegate solenoid. I had a customer that had the solenoids there but all the nipples were brocken flush. (It still looked as though they were connected) They will cause very abnormal behavoir.

That said, after i fixed that car and tested it at my place( sea level..10psi), I drove it up to the customer@1500ft above sea level). I had a boost rise of 3 psi just from my sea level to his elevation. The air is also about 15degrees cooler there so that plays a role as well. Soo point of all this is that Kento is on the correct thought path , while you make sure that all controls are intact.And i went freakin nuts double checking everything over and over again before I admitted defeat to the elevation/air temp difference.

Retserof

iTrader: (1)

Thanks BigIslandSevens, I'll check my nipples.

The cooler air was dense enough that it offset the increase in altitude, so the 3 lb increase in boost you saw was probably due to much lower humidity than at sea level.

For combustion purposes, a change of 1 degree in air temp is about equal to a 100 foot change in elevation, or 0.01 inHg in pressure, or 10% change in relative humidity. Increases in altitude decrease boost overall, but I'm not sure what effect it has on boost spikes.

Kento

Negative, humidity doesn't have that much effect on barometric pressure.

The reason that the FD's turbo system gains boost at elevation is probably because the wastegate pre-control actuator is controlled by pressure flow through a rubber hose with a pill restrictor inside. At higher elevations, the thinner air takes more pressure before it will activate the wastegate actuator, thus the increase in boost (and also the spike, due to the incrementally slower changeover by the CRV and CCV).

Retserof

iTrader: (1)

So, thinner air at higher elevations slows the turbo controls and contributes to spikes? I figured it would be self-compensating since the pre-contol and wastegate actuators are driven by both boost pressure and engine vacuum.

Also, I found this on autosportracetech.com:
"Boost Gauge readings at above sea level?

Kento

It can't be "self-compensating", because the mechanical controls and actuators of the turbo system don't know what the ambient barometric pressure is. The pressure and vacuum actuation work against springs and diaphragms. The turbo pre-control only reacts to pressure from the primary turbo (which, as described before, requires more work to actuate due to the thinner air). Although the ECU can sense ambient pressure to change fuel mapping, its control over the wastegate is somewhat poor at best.

I thought about that myself when I first had the problems at altitude, but it should be noted that I was barely at 2000 ft, not 4500 ft. Also, if the boost gauge was giving completely false readings (I know they'd be skewed to some extent due to the aforementioned calibration) and the ECU was able to compensate for the higher altitude, then why did it hit the fuel cut at 6000 rpm? This was long after the transition, and was due to the ECU sensing extended boost at 12-13 psi on the stock system. The car's turbo system worked flawlessly at lower altitudes.

Retserof

iTrader: (1)

Sorry -- my last post was getting off topic and I can't find the Edit button. Only the secondary turbo control has both pressure and vacuum lines.

On the original question of overall high boost and spikes with a stock setup, wouldn't restricted pill openings or internally blocked lines to the precontrol and/or wastegate actuators have the same effect as disconnected lines?

If the pill openings in the lines to the wastegate and precontrol actuators have been partly blocked or gunked up with PCV oil **** over the years, the smaller opening in the Wastegate Pill = an increase in primary and secondary boost and spiking, and the smaller opening in the Turbo Pre-Control Pill = reduced spike at transition, but more primary boost and primary spike.

Sorry again - didn't see your last post in time.

Kento

Note the last sentence in my post...

spike.spiegel

It's been a few months now, thought I'd give an update. While I acknowledge that boost may show higher here due to climate/elevation, I'm not totally convinced that climate can lead to a 14-5-9 pattern. It would be interesting to see if other Tucson FD's have similar patterns.

Anywho, I've been too scared to drive the car hard when it's hitting 14PSI so I pulled out the pill in the pre-control line today. The result is a tame 8-6-8. I'm not sure what I was expecting, but I'm definitely more comfortable with that than the spikes I was seeing before.

This is obviously just a workaround and the underlying problem still remains. Could it posisibly be a bad pre-control actuator?

Kento

Well, first you were saying you had a 14-8-10 pattern in your original post starting this thread. Now you're only getting 5 psi in the transition and 9 psi on the secondary?

If you don't think that elevation affects boost readings and reactions by the turbo system, then why are you getting 8 psi, when you should only be getting 6 psi with the pills removed? And remember, you're not at 4500 ft elevation....

spike.spiegel

Kento--

I should've mentioned that the pattern changed, or more likely, the pattern hasn't been consistent. I don't do that many pulls because I'm afraid of detonation. I do think elevation affects boost readings and reactions, but do you think a 14-5-9 can be attributed entirely to that?

Ibumar

Ok, first off. I doubt it was the pill to the pre-controll actuator that you removed. It had to be the one to the wastegate instead to give you the 8-6-8 pattern.

Anyhow, given your description of the boost pattern as 14-5-9, I would say that your pre-control is simply not functioning, and remains closed. The pre-control is used to spool up the secondary turbo and control the boost on the primary prior to transition. The fact that you were seeing such a high spike on the primary, followed by such a large dip at transition makes me think that the pre-control door remained closed and was not bypassing exhaust from the primary and pre-spooling the secondary.

I would check the vacuum system (hoses and solenoids) associated with the pre-control system and check the operation of the actuator. Also make sure that the actuator is still attached to the rod operating the flapper door in the exhaust manifold, and that it's set correctly.

Good luck, hope you figure it out.

dgeesaman

iTrader: (7)

I agree with Ibumar and Kento - the precontrol and wastegate solenoid is the most likely candidate to cause the spike. I suggest simply replacing the pair. If you have a mityvac and feel curious, you can tee into the line leading from the wg (and pc) to see if the pressure in the line has a corresponding spike as well. That would indicate a bad solenoid that isn't properly regulating the pressure in the actuator.

Dave

spike.spiegel

Thanks for the responses guys...I removed the pill in the longer of the two hoses, which according to this picture (http://www.autosportracetech.com/RX-...BigPicture.htm) is the pre-control pill.

Is it more likely to be a solenoid failure or actuator failure? What's the easiest way to test the actuator?