need some experts opinion

[superbyrd]

hi all. i have an 88 shelby z that i purchased on the boaed here from whiskeyman(thanks ferg) and i have been doing some mods and upgrades to the car and have hit a small stumble. here is what is done:
fresh tune up/ngk's, cap,rotor,wires,fuel filter,pcv,etc.
removed airbox,have k&n cone,2 1/4 pipe/flange with greedy BOV new 2 1/2"exhaust,no cat,dynomax ultraflo muffler
auto meter air/fuel and boost gauges
map blinded (zener diode)
other than those things,car is stock.
so here is the deal. car runs great,spools up pretty fast,but when the car hits around 10-12 pounds of boost, the car will back fire or pop a couple times real quick, then will keep on boosting.when it does this,it always pops the vacuum line off the wastegate solenoid.and this occurs if i am applying part or 2/3 throttle, if i punch the car to the floor, it doesn't do the popping. currently by the autometer boost gauge i have installed, the car is pulling 18 psi of boost. A/F gauge is staying on the next to last light bar on the rich,so fuel is fine. should the car be boosting that high with no grainger or MBC? would a change in timing or premium (93 or better) fuel help? any ideas would be greatly appreciated.

[detobias]

hose clamp (some people use zip ties) ALL your boost / vac lines ; a 'popped' WG line could cause overboost REAL FAST and kill yur motor

I never run less than 91 octane

[IROCNOROLL]

Quote:

Originally Posted by superbyrd map blinded (zener diode) other than those things,car is stock. so here is the deal. car runs great,spools up pretty fast,but when the car hits around 10-12 pounds of boost, the car will back fire or pop a couple times real quick, then will keep on boosting.when it does this,it always pops the vacuum line off the waste-gate solenoid.and this occurs if i am applying part or 2/3 throttle, if i punch the car to the floor, it doesn't do the popping.

Higher boost levels at WOT will be more acceptable to the ecu than part throttle high boost levels. Remember the ecu is blind to the peak or overboost you are creating by utilizing the Zener Diode on the MAP. It will be "seeing" a little less than 14.7 psi because of the diode. Also running less than WOT will probably result in a little less injector on time compared to WOT.

Quote:

currently by the autometer boost gauge i have installed, the car is pulling 18 psi of boost. A/F gauge is staying on the next to last light bar on the rich,so fuel is fine. should the car be boosting that high with no grainger or MBC?

As you have blinded the ecu to the real boost levels your reaching via the Zener diode, the ecu is attempting to control boost via the waste gate solenoid based on false information. When you are hitting high boost levels at less than WOT, you may be running lean, causing a backfire situation, or the ecu is attempting to cycle the waste gate solenoid and a combination of loose fitting hoses and higher boost pressures are pushing the hose off the WG solenoid. Remember the solenoid is usually open to atmosphere, venting. When the ecu cycles the WG solenoid, it closes the vent to build pressure back to the WG can itself. If there is big pressure and the solenoid is closed, the hose might be pushed off.

Quote:

would a change in timing or premium (93 or better) fuel help? any ideas would be greatly appreciated.

Yes, for sure run the highest octane fuel you can find, especially if you are pulling to 18+ psi actual boost levels.

Make sure the hot (cooling fan cycling) base timing at idle with the CTS on the side of the thermo housing unplugged is 12 degrees at the max, and if you are pushing up to 18+psi boost, maybe pull it back a couple or three degrees.

Then maybe consider losing the Zener diode, as they are usually the root of more evil (read damage and carnage) than good. Get a cal that matches the rest of the set-up you are running, and work up from there. Smarter and safer. FWIW

[detobias]

^ some good stuff

is there any chance you can watch your A/F gauge when you are experiencing this misfire ? it is possible you are running lean as IROC suggests in the region of <WOT

I think our computers tend to stay in closed loop up to 3-5 psi, before going open loop ; sounds like you *should* be above this point ...

and IROCs point about yur boost solenoid is also well stated; if it was me I would prolly run a grainger or other MBC for 2 reasons: eliminate the solenoid / wiring / vacuum plumbing and their potential for problems; and, actually have some Control over the boost level

lastly MAKE SURE you have a 1/2 watt or better a 1 watt zener ; I was running a 0.25 watt and it would behave unpredictably, causing me Lean issues, and it was difficult to trace the problem because it was sporadic

[superbyrd]

i watched the A/F gauge when it does this pop, and it is staying in the "ideal-rich" area. and it is staying in the "rich" area at WOT. as for the solenoid,i took the vacuum line off the solenoid and put that line straight on the map sensor port, disabling the WG solenoid. seemed to take some of the pop out. and yes, i have a 1 watt zener diode. i know that a stage 5 cal computer,3 bar map and +20's are in my immediate future. i plan on setting my boost total at 22psi. then i want to get it to the track.

[IROCNOROLL]

Quote:

Originally Posted by superbyrd i watched the A/F gauge when it does this pop, and it is staying in the "ideal-rich" area. and it is staying in the "rich" area at WOT.

If this is true, then you are trying to believe and rely a slow reacting 02 cell, as a misfire or a backfire to either the intake or exhaust side will push unused 02 into the exhaust, and the cell should at least momentairly drop like a stone responding to the extra air as a lean. Even if a momentary situation, sooo, you may be seeing false info. This may be a coated 02 cell due to age, silicate contamination, glycol contamination, etc. This can also be due to contamination to the fresh air side of the 02 cell tip via the fresh air vent, though unusual.

[superbyrd]

okay. just replaced the oxygen sensor a few minutes ago,warmed up the car and drove it. i watched the gauge very carefully. about the 4-5th time i eased on the boost,it popped,when it popped,and cut out for a split second like it usually does, the gauge went to lean,only while it was cut-out.as soon as it picked right back up,it went to "ideal-rich". gonna take a little timing out of it and put some 94 sunoco in there tomorrow. i got some 112 octane VP race gas (about 3 gallons) think i will throw that in and see how the car likes it.

[superbyrd]

ok. this sounds dumb to me or maybe i am just not thinking straight. when i initially put a BOV on the car, i was using a stock 88 T1 BOV,vacuum line,and a pipe i made for the upper hose. anyway, when i got this new pipe with the flange and new aluminum BOV,i took all that stuff off and hooked up the new BOV. i didn't re-use the little one-way vacuum check valve on the new BOV and didn't think it needed it. well,for the hell of it today,i put that little check valve in line on the car. the popping is gone.period. no stammer,no pop,justs boosts up and goes.i have driven the car for over an hour,and no problems. only thing is.........now it makes exactly 15psi of boost on the autometer gauge!!!
what the hell? i guess the new parts will solve that problem. hehehe.

[Mystryguy]

i'm not positive but ive heard that our "ideal" o2 voltage is all the way full rich on the autometer disco gauge. I prefer seeing a straight voltage reading myself and at LEAST an egt reading>15psi. I always threw in a mix of 110 when going above 15 for safe measure even though it probably shouldnt need it (unless you get bad gas or 91 or less octane).
Read your plugs after the misfire, see what they tell you!

[roachjuice]

diodes don't ruin motors. lean conditions do. i've ran a stockish (mopar stage 2 lm) computer for awhile now and no problems. i run 16 psi of boost on stock injectors and fuel pump and 91 octane (oklahoma sucks the big one when it comes to gas). i don't think i can go anymore than that. but just read the plugs and keep an eye on things while wot. if it EVER spikes less than green at wot let the fuccckk off. loose the race do what ever. but atleast you still have a healthy engine to fight another day. but that little check valve lol at that. i can't believe that fixed it. keep on keeping on.

[IROCNOROLL]

Quote:

Originally Posted by Mystryguy I'm not positive but Ive heard that our "ideal" O2 voltage is all the way full rich on the autometer disco gauge. I prefer seeing a straight voltage reading myself and at LEAST an EGT reading>15psi.

Narrow band 02 cells are only as reliable as the last head gasket failure, or wrong silicone sealer use. Wide bands can also be contaminated and their performance and speed of change will suffer. If you are trying to watch a digital volt meter, the display refresh rate of most DVOM's is about 1/5 the speed of the crossover rate of the 02 cell itself. In other words, your only seeing maybe 1/5 of the big picture every second of running time. Analog meters are death to an 02 cell, as the cell, which is really a small battery, will eat itself trying to supply the current required to drive the analog meter movement. 02 cells are the main reason the industry adopted the 10 meg/ohm per volt meter standard like 25 years ago. If you really want to monitor the 02 real time, a Data Storage Scope, graphing meter or a graphing high speed scanner with sufficient storage time and capacity is the only real answer to seeing it "as it happens", and then being able to review it along with boost attained and any other parameters you chose to watch. EGT's again are useful as a comparator, but placement is everything. Remember, the EGT temps your seeing are substantially less than the actual temps attained in the combustion chamber. The shape of the exhaust manifold runner to runner, and the differences in flow this causes will mess with the readings too. Just like real estate, it comes down to location, location, location.

Quote:

I always threw in a mix of 110 when going above 15 for safe measure even though it probably shouldn't need it (unless you get bad gas or 91 or less octane).

An adjustable or rising rate fuel pressure regulator can also be utilized along with the graphing readings above to fatten up the boost fuel delivery to help keep things happy at the 15 - 16 psi range, provided you keep surge and creep under control. Also remember that the actual turbo your using along with whether the air charge is inter-cooled or not will determine if those boost levels are actually gaining you anything. A Mitsu at those levels is pretty much past it's comfort zone for efficiency, and mostly your beating the air and maybe the engine to death for nothing.

Quote:

Read your plugs after the misfire, see what they tell you!

With unleaded and worse, oxygenated fuels, plug readings are difficult to do, unless things are really way wrong in the combustion chamber. And then, if it shows blistering or material transfer on the tips, your probably too late anyways. Even good / marginal color is more difficult to judge with these fuels.

[IROCNOROLL]

Quote:

Originally Posted by roachjuice diodes don't ruin motors. lean conditions do. I've ran a sickish (mopar stage 2 lm) computer for awhile now and no problems. i run 16 psi of boost on stock injectors and fuel pump and 91 octane (Oklahoma sucks the big one when it comes to gas). i don't think i can go anymore than that. but just read the plugs and keep an eye on things while wot. if it EVER spikes less than green at wot let the fuccckk off. loose the race do what ever. but at least you still have a healthy engine to fight another day.

Diodes and various bleeds too, in the hands of the uninitiated allow them to run the lean a/f levels that kill the engines. They blind the ecu to the real world boost levels, and prevent it from fueling effectively above say 14psi, as well as saving itself, and somebody's wallet. Running either an off the shelf or infinitely tunable ecu that recognizes, and is fully capable of controlling fuel, and timing retard correctly at the target higher boost levels is the best real way to save the engines.

Quote:

but that little check valve lol at that. i can't believe that fixed it. keep on keeping on.

What brand of BOV is this? Does it have more than one vacuum port on it? Wonder if the vacuum line was connected to the correct port if it is a multi port BOV? Or if it is adjustable, if it is set a little light on the calibration, and is actually doing what it was tuned to do by the manufacture?