Boost Gurus: Help solve perfect 10-8-10 then wild bouncing between 7-9 lbs
 

Hi folks:

The car: 93 touring 38K on it.

Bought the car in bone stock shape five months ago. Car drove great, but seemed to die on the top end. I assumed this was the restrictive DP / exhaust.

Recently made the following mods:
Fluidyne Rad
M2 intake
3" downpipe
Viton hoses & check valves
Boost gauge
Efini y-pipe
Still using the stock cat * cat-back exhaust.

Since the mods, the car drives great except it still seems to die off a bit above 5500 or so. Same behavior as when it was stock. Since I now have the boost gauge, I can see what is going on a bit more. I get a perfect 10-8-10 pattern up to ~5K. Boost gauge needle moves smoothly and boost recovery after transition is immediately back up to 10. Almost immediately after that though, the boost pressure drops and starts to fluctuate pretty wildly between 7 and 9 pounds up to redline. Other than the slight loss in power, the car drives great (no hesitation, etc.)

What I know:
- There are no exhaust leaks at the DP
- The correct pills are in the correct lines, pointing in the right direction (I was pretty meticulous)
- No holes or tears in the intercooler piping. I recently cleaned & checked everything.
- Y-pipe & turbo housing bolts on tight (torqued to spec)
- I am using the stock clamps on the 1" hoses

I have been doing a ton of research on possible problems, but there are a lot of things to check. I suspect the problem was present in the car before the modifications based on the similarity in "before" and "after" performance. I would appreciate any feedback or direction on what to check first. My thoughts so far:

1) Possible clogged main cat (although I would think this would cause steady lower boost, not the wild 2 psi oscillation). Anyone have any experiences with this?
2) Leaking 1" hose die to stock clamps ( I can rotate the hoses by hand with some effort with the clamps on). A light leak might explain the oscillating boost.
3) Some problem with the wastgate control, vaccum, etc. This one is where my expertise is the thinnest, so I could really use some advice.

All input appreciated. - Phillip

How the hell you have a perfect 10-8-10 with these mods and without a EBC,or a manual BC?

Hi (chuckle),

I am not sure what you mean. Could you clarify?

- Phillip

Like you said, a clogging cat should steadily push down boost as the RPMs increase. Unless something is broken loose and bouncing around in the cat canister, I can't see an intermittent blockage. You can unbolt and lower the cat to inspect it, but I doubt it's the problem if it doesn't rattle when you shake it or drive over bumps.

The bouncing boost level is a bit puzzling to me. Perhaps an intermittently failing check valve or bad electrical connection is causing it - but in either case it would be just as likely to happen at any rpm where 10psi is happening.

I can also envision a closed-loop problem where something vents/restricts the boost, but is alleviated when the manifold pressure goes below 7psi, but occurs again once boost climbs back. That's my best theory.

So following that pet theory, I would first look at the wastegate system.

1) Pressure in the wastegate line that causes blowby at the boost pill, or other leakage in that line could (in theory) produce a closed-loop oscillating. Check the hose carefully for leaks, and wrap a zip-tie firmly around the wastegate line directly over the boost pill. Also inspect the nipple to the compressor elbow to be sure it's secure.

2) Another possibility is the wg solenoid not working well at lower duty cycles (leaking) - to test that, I would swap in a spare good wg/pc solenoid pair. Or if you can't find a spare, switch both hoses and the electrical connectors to the pc/wg pair. If your boost pattern changes (probably won't get 10-8-10), it's bad.


PS:
Your mods are fairly mild. As long as the boost stays at 10psi max, there is little to worry about. Some people will start to see elevated boost with 2 or 3 mods. MBCs and EBCs aren't necessary for near stock boost levels - but they are very popular.

Dave

Another possibility is a collapsing primary turbo inlet hose.
(source: http://www.autosportracetech.com/RX-...leshooting.htm, under the topic Primary Turbo Inlet).

Collapsing hoses often do so suddenly, and will pop back to shape when vacuum is reduced. The load on this hose is greatest at high rpm max boost. Try a new one (or borrow for testing sake) to see if that fixes it.

Dave

Phillip,
You are leaking boost somewhere. When the pipe collaspes it just reduces the boost to say 7 or so but it doesn't fluctuate wildly. You're pipe seals etc...are good to about 7 psi then something starts to leak. Check the UIM gaskets, TB gaskets, Elbow Gaskets and move on down the line from there.

Good luck,
Fritz

With the mods you have listed, and no boost controller, you should be seeing increased boost levels. I would have expected at least 13 psi, which would be too high for your stock ecu. It's likely that you are hitting fuel cut. Perhaps your boost gauge is giving you readings that are too low.

I suggest that you verify your boost pattern with another gauge.

About the boost leak - 10psi is 10psi at any rpm - and a leak generally responds to pressure, not the speed of the flow. So the fact it consistently happens at 5k is does not agree. But those 1" hoses should be fairly secure - under 10psi that's a significant load and anything is possible.

I think Adam_c has a really good point - be sure that boost gauge is spot on before running down the turbo road. Any 0-15psi or greater pressure gauge can be teed into the manifold to verify it.

Dave

Updated info: Some progress made
 

Thanks for all off the input folks. This is great!

I tried the easy thing first and replaced the spring clamps on the 1" hoses with SS band clamps. I saw an improvement..I know have the following boost pattern in 3rd gear:

11-8-11-10-9-fluttery 8to9

So.. I am getting more boost and the boost does not start to bounce until after 6,500 or so now. That is up from ~5,000 before the clamps. So I think we are on the right track. Car pulls noticeably harder than before.

I have also notices that I am getting ~ 14 on the vaccum at idle (Down
from 16-17) when stock...so it looks like I still have a small vaccum leak somewhere. It's possible vaccum leak turns to boost leak under bost.

My next steps (I'd love input):
1) Try the starter fluid vaccum leak test to try and find the leak
2) Install the PFC / commander I have sitting around to control the overboosting and ensure proper fuel delivery
3) Check the orientation of all of my check valces
4) I am open to input....

Thanks again everyone! Keep the advice coming! - Phillip

1) Keep looking for leaks or loose connections. Clean the engine bay, take it for a drive, and look for oil sprayed somewhere. Look for blown gaskets, perhaps near the ACV or LIM. Look for popped or missing hoses also, use the vacuum hose diagram to check it again.

2) Test the MAP sensor

3) Test the wastegate actuator for smooth operation. Buy a Mityvac or borrow one from Autozone (free rental). Cap one nipple on the actuator, and apply pressure. It should move smoothly in and out as you apply more pressure. You can also tee into the line between the actuator and wastegate solenoid, and using a long line, monitor the pressure being controlled by the wastegate solenoid. Although the pressure might appear to jitter very fast (due to the duty control, some gauges have enough damping you can't see the jitter) it should resemble a steady pressure. If the wiring or solenoid is at fault you'll see this pressure varying with the boost output. Also test your boost gauge with the Mityvac - if the mityvac doesn't have a pressure gauge, at least see that the vacuum side is calibrated.

A few questions:
- did you have your injectors cleaned/flow tested during the hose job?
- when was the fuel filter last replaced?
- have you checked for any phantom ECU codes?
- when were the plugs and wires last changed?

I personally would not install a PFC permanently until I felt things were running right, but I believe you can install it in such a way that you can easily swap in the stock ECU if required. With the PFC in you'll have access to a LOT more data that might help diagnose the problem. 11psi is more than stock, but not necessarily risky unless it approaches 12. (Just keep filling with Sunoco 94, avoid WOT except in testing when you can watch the boost gauge, and tune it down to 10 before the weather cools).

Dave

I'll bet, changing out the stock catback to a decent aftermarket one will make the boost steady through redline (given the rest of your mods).

I have the same EXACT expierence with the stock exhaust in place...

Muffler, wow.

Are you suggesting there is a pulsing/resonating going on, or simple flow restriction?

In either case, I would be careful with the boost level - adding the catback could easily push that 11psi higher still unless you put in bigger wastegate pill, or install a manual or electronic boost controller.

Dave

Great info: Please see responses:

"1) Keep looking for leaks or loose connections. Clean the engine bay, take it for a drive, and look for oil sprayed somewhere. Look for blown gaskets, perhaps near the ACV or LIM. Look for popped or missing hoses also, use the vacuum hose diagram to check it again."

Will do. Motor is already immaculately clean - so that's not a problem.

"2) Test the MAP sensor"

Can you explain your thinking as to why the MAP might be bad (just so I know).


"3) Test the wastegate actuator for smooth operation. Buy a Mityvac or borrow one from Autozone (free rental). Cap one nipple on the actuator, and apply pressure. It should move smoothly in and out as you apply more pressure. You can also tee into the line between the actuator and wastegate solenoid, and using a long line, monitor the pressure being controlled by the wastegate solenoid. Although the pressure might appear to jitter very fast (due to the duty control, some gauges have enough damping you can't see the jitter) it should resemble a steady pressure. If the wiring or solenoid is at fault you'll see this pressure varying with the boost output. Also test your boost gauge with the Mityvac - if the mityvac doesn't have a pressure gauge, at least see that the vacuum side is calibrated."

Will do

"A few questions:
- did you have your injectors cleaned/flow tested during the hose job?"

No - injectors have never been out.

"- when was the fuel filter last replaced?"

100 miles ago

"- have you checked for any phantom ECU codes?"

Yes...no codes present

"- when were the plugs and wires last changed?"

Wires are stock, plugs about 5k ago

"I personally would not install a PFC permanently until I felt things were running right, but I believe you can install it in such a way that you can easily swap in the stock ECU if required. With the PFC in you'll have access to a LOT more data that might help diagnose the problem. 11psi is more than stock, but not necessarily risky unless it approaches 12. "

Saw a brief spike to 12 at throttle tip in in 2nd gear. How worried should I be?



(Just keep filling with Sunoco 94, avoid WOT except in testing when you can watch the boost gauge, and tune it down to 10 before the weather cools).

Dave

Thanks for all of the input! - Phillip

Yep, some catbacks are restrictive enough to cause that. There was a thread a while back about a guy running a full 3" exhaust with an older restrictive HKS catback. Everyone kept telling him he was "doing wrong", but his boost never spiked or crept.

Then, he changed his catback and viola, out of control boost. ;) Sometimes it doesn't take much if it's right there on the edge.

Updated Info: More Input Requested
 

Hi folks,
I am in the process of diagnosing this issue: I have tried the following things:

1) Tested vaccum & pressure chambers: Both work properly.

2) Tested charge relief and "blowoff" valve: Both work properly.

3) Disconnected (unplugged) wastegate solenoid to run strictly on spring pressure on the wastegate. My thinking here is that this would isolate problems with the vac system & ecu control of boost.

When I did this, I had a consistent 7 psi below 4500rpm. Above 4500, I would get 5-6 psi and the same "bouncing" boost gauge at higher rpm (+/- psi). This seems to indicate a boost leak vs a control issue or a clogged cat. Pressure above 4500 was slightly lower in 2nd gear vs 3rd.

4) When doing a system pressure test (plugges intakes with Tennis Balls, etc. and hooked up to air compressor) I noticed a very substantial air leak at the oil filler neck o-ring. This was being pressurized via the secondary pcv vent line to the primary turbo (the pcv valve works properly). The leak here was so significant, the system could not hold enough pressure for me to fully test for other leaks. Initially, there did not seem to be another significant leak.

5) When I removed the spark plug wire for the rear leading coil, the tip broke off in the coil due to a massive amount of corrosion (and accompanying white crud). It is possible that this was causing some ignition problems at high rpm.

My next steps:
1) Clean up terminal on leading coil (it tests out ok) and replace spark plugs & wires

2) Replace o-ring on oil filler neck and retest.

My questions:
- Would the large air leak at the bad o-ring on the oil filler neck leak leak boost under normal operation conditions? Not sure if this would normally be pressurized the same way as when the air compressor is connected.

- Any chance the corroded spark plug terminal is a contributing factor?

- Phillip

The corroded plug is almost certaily a factor.
The leak at the oil filler should have no effect on boost or vaccuum.

You haven't lived till...
 

Here's a new use for the FD - a brake cleaner cannon!

So I changed the plugs and resealed the oil filler neck. After that I plugged off the secondary pcv line (from turbo neck to oil filler neck) so I wouldn't get a pressure leak through there.

Next I went back to pressure testing the system. At first I was using tennis balls to seal the system, but the fuzz on the tennis balls was allowing air to escape - so I substituted empty cans of brake cleaner ( I go through brake cleaner like a fat man through donuts so they were easy to find).

This worked great until I upped the pressure to 15 psi or so..then BAM :eek: a can of brake cleaner launches clear across the garage! This was so funny I of course had to try it again. :p:

So after all that...I couldn't find any other leaks at all. I would get a slight muted hiss from the UIM, but it was hard to tell if it was just air passing through it or a small leak somewhere. I ran my hands underneath it, around the rats nest, etc. and never did find anything. At this point, it does not appear to be a boost leak. The only "leak" I found was through the secondary pcv valve line into the oil filler. At this point, that may just remain plugged!

I am hoping that the corroded spark plug wire was the problem.

Any and all suggestions, insights, etc. welcome. I appreciate it.

- Phillip

there should be a 1 way valve on that neck.

Which neck?
 

Hiya,
Just so I understand - are you saying there should be a one-way check valve on the line that runs from the vertical tap off of the oil filler nect over to the y-pipe? I do not believe there was one originally - although someone mentioned a restrictor pill - but I have not been able to corroborate that....

- Phillip

PFC experiences
 

Hi folks,

I recently installed a PFC prior to changing over to a high-flow cat. I wanted to get the boost control sorted with the current set-up prior to adding the high-flow cat.

My PFC experience:
- Install was very straightforward - I am using the cigarette lighter mount detailed in a few other posts. This works great and positions the PFC very well.
- I followed the idle-learn process and things went very well. The car occasionally hunts for an idle when you come to a stop, but settles down quickly. This is already starting to reduce after ~100 miles
- The AC works normally
- Boost control works effectively as well.

What I noticed after installing:
1) The o2 sensor is dead - probably not helping my fuel mileage.
2) While the boost still oscillates at high rpm, the PFC is able to effectively hold boost at higher rpm, where the blind stock ecu could not. So instead of boost bouncing between 6-8 above 6000rpm, it now bounces between 8-10.

With the added boost, the car is noticeably quicker and no longer has the running out of breath feeling above 6000.

Next step is to replace the o2 sensor and install the high flow cat. I am hoping the cat removes some of the oscillation. Note that I am running the stock cat-back still (and plan to retain it for now).

That's all for now. I am currently a big fan of the PFC.

- Phillip