Timing advance and fuel cut

[gob4sho89]

Around 15psi, My car studders like its hitting fuel cut, and my timing jumps from 18-22 all the way to 32-36. Is this what timing does at fuel cut? thanks.

 

[Zack Huffman]

Boost leak.

 

[Ceddy]

Boost Leak +1

Your high pressure leak is making the ecu see more air so it is adding timing.
And since that extra air leaking out your running horrible rich and shuddering.

 

[snox135]

Fuel cut feels like hitting a brick wall. So if your studdering it's not fuel cut.

Boost leak- agreed

 

[gob4sho89]

I see -28psi at idle, but I will go do a boost-leak test right now, thanks. I had 0 leaks at 10 psi, and didnt think about it possibly leaking at the higher pressure. Thanks for the quick replies.

 

[gob4sho89]

Ok, now I am really confused. I did a boost leak test, and my system held 34psi for 5 minutes without going down at all, with the air pump off. I didnt hear any hissing, or bubbling or anything. Anyone have any more ideas? I know its not knock, because my timing advance increases. thanks for the quick replies!

 

[snox135]

Could be your fuel filter.

 

[gob4sho89]

nope, replaced my whole fuel system last week, pump, lines, filter, rail, injectors, regulator. I double checked and it is just like new. Any other ideas?

 

[oldman]

1. -28 in HG (not psi) at idle is crazy unless you're idling at 1500 rpm and your ignition base timing is way off.

2. 35 psi for 5 min without dropping is unheard of, where are you placing the leak tester.

3. What are your adjustments on the SFAC for the 650s?

 

[gob4sho89]

ok, it droped like 1/2-1 psi, placed on the inlet of the turbo,
settings on my afc are -21 to -28 for high, -24 to -35 for low
my idle was around 1100rpm, now I am seeing around -18HG to -20HG as my Idle goes from 800rpm to 860rpm.
? Thanks again for the help.

 

[oldman]

ok, it droped like 1/2-1 psi, placed on the inlet of the turbo,

That is good, no one I know has never come close to that, myself included.

settings on my afc are -21 to -28 for high, -24 to -35 for low

Sounds pretty normal but keep in mind that one of the biggest draw back of a piggy back system is timing advance, the more air you remove, the more advanced the timing. Is your mas hacked?

my idle was around 1100rpm, now I am seeing around -18HG to -20HG as my Idle goes from 800rpm to 860rpm.

I thought you said it was -28 inHG? Check your valve timing then make sure your ignition base timing is set to 5* BTDC.

 

[gob4sho89]

it was -28, but it changed when I lowered my idle.
My mas is not hacked.
Base timeing is right on.
Is there anything that could leak boost only when the car is running? I cant think of anything...

 

[Calan]

I did a boost leak test, and my system held 34psi for 5 minutes without going down at all, with the air pump off.

Wow.. I didn't know that was even possible. I would think you would have at least 2-5 psi leakage through the valves/rings/etc. if nothing else ... especially at 34psi after 5 minutes.

EDIT:

<<< no boost expert, but are you sure you performed the test correctly? This just seems WAY out there from what I've heard and seen.

 

[snox135]

The air pump was off, but was there a air tank still supplying air?

 

[oldman]

gob4sho89, some questions for you.

1. What are you using to pressurize the intake with? What kind of boost leak tester?

2. Which brand and model of boost gauge are you using?

3. Is xs power MBC the same as TurboXS MBC? If not, is it a bleeder or ball and spring type MBC?

4. How is the MBC hooked up?

5. Are you still running the T25?

6. Are still running with the stock 2G BOV? Is it recirculated?

7. What are your low, mid and high fuel trim?

8. How did you check your ignition base timing? What is your timing at idle?

9. Why are you idling at 1100 still? Are you not able to bring idle down to 750 like where it should be?

10. What is your ISC and TPS reading at idle?

Please answer each question in detail so we can help you better.

 

[Zack Huffman]

Please answer Bruce's questions.

I don't think the leak test was done correctly. Can you explain exactly what you did? I think 34psi with no leaking is the highest I've ever heard of someone holding steady on a normal IC setup, and 20+ inches of mercury vacuum, even at a 860rpm idle, seems a little suspect as well.

Maybe you should check your cam sprockets again to make sure your T-belt didn't jump a tooth on one of the gears, shorter I/E valve overlap might cause that kind of vacuum at idle.

 

[gob4sho89]

1. I am using the air system at a local shop, my tester is a quickconnect one way check valve welded to a pipe, with a coupler on the end. I hook it up to the inlet of my turbo, and disconnect the air hose when it reaches the desired psi.

2. Autometer ultra-light

3. I am not sure, It was in the glove box when I baught the car.

4. The boost controller is hooked up between the intake and bov.

5. I am still running t-25, I am putting on a 57trim bb when the weather turns nice

6. I am running a 1st gen BOV that is lightly crushed and 100% recirculated.

7. When you say fuel trims, are you talking about what my logger is picking up while I do a poll? Short term fuel trim?

8. It was done at a local shop when they changed my timing belt, and I had it checked by 2 other shops on the same street. my timing advance at idle is around 5-8degrees.

9. Idle was brought down to 800-850 last night.

10. I think I took out my isc when I took out cruise controll. TPS is reads 0-.5 at idle and goes up to 100 when I put the pedel to the floor. The readings seem correct.

Thanks for the help everyone!

 

[gob4sho89]

The mv came down when I lowered my Idle. The boost leak tests are done when the motor is warm, if that makes that big of a difference. I just went and checked my timing this morning and the Timing marks on the cam gears still line up perfictly.

 

[DJYoshaBYD]

what do you mean your MBC is hooked up between the intake and the BOV? Thats not right at all... It should go from the J-Pipe to the wastegate... there should be ABSOLUTELY NOTHING hooked up or spliced into your BOV line... That could actually be the problem if the BOV doesnt work right... I believe what your experiencing is called compressor surge... I could be wrong, but I KNOW Im right when it comes to that BOV... needs to be checked

 

[gob4sho89]

So I need to drill a hole in my turbo's j-pipe, and tap in a nipple for my mbc? It is working fine, my problem is at 15psi, and wot. My mbc keeps it at 15psi, I am not having any trouble with creep, spike, over or under boosting, or anything like that.

 

[oldman]

1. I am using the air system at a local shop, my tester is a quickconnect one way check valve welded to a pipe, with a coupler on the end. I hook it up to the inlet of my turbo, and disconnect the air hose when it reaches the desired psi.

What was the regulator set to on the local shop's air system? Is there a built in gauge on the tester? Were you present at leak test every step of the way OR are you just going by what the shop told you.

2. Autometer ultra-light

There are many different models for ultra-lite ranging from 30-30 to 0-100, which one do you have?

3. I am not sure, It was in the glove box when I baught the car.

Is it an EBC or MBC? If it's a MBC, is it a bleeder or ball and spring? If you don't know, check it.

4. The boost controller is hooked up between the intake and bov.

This alone is a boost leak (a big one at that), your BOV is open during WOT because the wastegate pressure relief hole is bleeding pressure off the BOV line regardless if you have EBC, MBC, bleeder or ball and spring.

6. I am running a 1st gen BOV that is lightly crushed and 100% recirculated.

A lightly crushed 1G BOV will hold about 20psi at best, it certainly will not hold 34psi for 5 mins.

7. When you say fuel trims, are you talking about what my logger is picking up while I do a poll? Short term fuel trim?

Yes from the logger but I'm talking about long term fuel trim, low, mid and high long term fuel trim. I suspect they're off and inconsistent at best since you're lacking an AFPR and are using SFAC to compensate.

8. It was done at a local shop when they changed my timing belt, and I had it checked by 2 other shops on the same street. my timing advance at idle is around 5-8degrees.

Your idle timing should bounce between 8-10 if in fact the base timing is set to 5* BTDC, were you there when they used a TIMING GUN, with the timing plug properly grounded, to check your ignition base timing? How did any of them check ignition base timing with your car idling at 1100+ rpm?

9. Idle was brought down to 800-850 last night.

How did your do this? Did you properly ground both timing plug and diagnostic port when adjusting the BISS? Why can't you bring it down to 750? What is your vacuum reading now?

10. I think I took out my isc when I took out cruise controll. TPS is reads 0-.5 at idle and goes up to 100 when I put the pedel to the floor. The readings seem correct.

How can you not know for sure if the ISC has been removed? If removed, was the passage properly blocked off? Is your FIAV functioning with coolant lines connected to the TB? If not, is it properly blocked off?

Your TPS should not vary from 0 - .5 volts, it should be a constant number, what is that number?

 

[gob4sho89]

1. The shops air pressure was turned down to 35psi, yes, there is a gauge on the leak tester, and I was standing right there, hooking it all up myself, the whole time. They charge me 0 to just borrow their equipment.

2. 30-30

3. MBC, http://www.dsmtuners.com/parts/product_info.php?cPath=3_143_60&products_id=323

4. K, thanks, i will fix that.

6. We had Caped off the bov, and the part where the re-circ tube goes on the intake, because we couldnt find any leeks at 20psi, and in order to step it up, we had to plug them.

7. I have an aeromotive afpr and am using the safc to compensate for fic 650cc injectors

8. This afternoon, when I started the car, timing was holding at 9, not changing from 8-10 (is this ok)and I am idleing at 800rpm. When the timing was checked, the car's idle was at 750 spot on, but it was a little rough, so I turned it up a little, which was a little too much. I am always there supervising/helping when anyone is working on my car.

9. Yes, I did follow the proper procedure when adjusting the idle, vacume is reading 16-18 at 800rpm

10. Sorry about this one, my ISC has not been removed, dont know what I was thinking.
TPS reads 5 on pocketlogger and 0 on my s-afc.
Thank you for being patient with me and helping me to work through this.

 

[oldman]

1. The shops air pressure was turned down to 35psi, yes, there is a gauge on the leak tester, and I was standing right there, hooking it all up myself, the whole time. They charge me 0 to just borrow their equipment.

A gauge on the leak tester, not on the air system regulator right? Can you post a picture of the tester? I'm hammering you on this because claiming to have held 34psi in the entire intake tract for 5 mins with only 1-2psi drop is almost like someone claiming to bench press 400lbs with one arm, I like to get to the bottom of this.

3. MBC, http://www.dsmtuners.com/parts/product_info.php?cPath=3_143_60&products_id=323

Was the MBC disconnected during the leak test?

4. K, thanks, i will fix that.

This alone could very well be the reason why you're bogging at 15psi, you're not hitting fuel cut BTW.

6. We had Caped off the bov, and the part where the re-circ tube goes on the intake, because we couldnt find any leeks at 20psi, and in order to step it up, we had to plug them.

Is there anything else you would like to share with us? You didn't remove the UICP from the TB elbow and cap that off during the test did you? What else did you have to do to get to 34psi? Why did you claim to hold 34psi for 5 mins with having to block off the BOV? Didn't you think it would be extremely mis-leading to readers, especially people who are trying to help you? This isn't a contest about who can hold more pressure, this is about helping you and no one else.

7. I have an aeromotive afpr and am using the safc to compensate for fic 650cc injectors

What is your fuel pressure at idle?

 

[gob4sho89]

1. OK, the more I thought about 34psi, the more it didnt make sense. I went back and inspected my tester, I sat looking at it for about 30 minutes. I then realized how stupid I am. I drove to the gas station about 1 mile away from my house, and hooked up my boost leak tester there. I did not put it on my car, just stuck it on the hose. The pressure was at 75psi on the gauge in about 1/2 a second. I un-pluged it, and sure enough that 75psi stayed put. I had overlooked the check-valve that was built in to the gauge(I didnt think one was there.) I had the gauge welded up backwards, so it was holding pressure out of my system, and the other check valve was holding the pressure in from the other side.. I proceded to put it on my car, hoping that some how putting it on my car would make a difference, and looked at my boost gauge and it read 0. While doing the boost leak test, I had only been looking at the gauge on my tester. I feel so stupid. This evening I will put together a simple, gauge-less, boostleak tester. I should be able to do a boost leak test tomorrow. I will post my results some time tomorrow evening.

My fuel pressure is 43.5-44psi with the vac. hose off. (something I know is right on this car)
I went to fix how my mbc is hooked up, and found that the outlet on the compresser housing was pluged with jb weld . Does this mean that I have to take off the turbo, drill and tap it, or is there another way?

 

[Calan]

Well.. first off.. kudos for finding the problem with your boost leak test. Those results were just WAY to improbable.

As for the MBC, you want the shortest path from the MBC to the turbo outlet. My turbo/J-pipe didn't have an outlet, so I drilled and tapped a fitting into the J-pipe. It's probably not the most efficient connection from an airflow point of view, but it works until I can get a weld bung on it and do it right.

If you had a tap that was JB welded, it might or might not be easier to drill and tap that vs. finding a new tap. Hard to say with out seeing it.