HELP! lean out pop

[LITLV6]

If someone could shed some light on this one i would really appreciate it. I have an 86 T-top GN with about 90k. It has a mild chip from about 7 years ago, (i bought it in march 07) auburn posi, 26 or 2800 rpm redline converter with what feels like some good internals in it. I have a pro comp ultralite tach, boost, temp, oil, voltage, and fuel gauges, caspers knock gauge and a scanmaster 2.1.

Ok, so the problem is for awhile after i bought the car it would boost, then after about 15psi it would make a loud popping sound once twice or a few times depending on if i kept my foot on it long enough. when it makes the 'pop' the boost gauge drops then comes back up. i changed wires to Taylor 10mm, replaced my TPS which is set at .42 at idle. after screwing with it it quit doing it. now a year and half later its back. the car will boost about 19lbs. in first gear and i have noticed by feathering the pedal that when my fuel pressure guage dips to about 38lbs.( i have it set at 52PSI with no vacuum) is when this occurs ...... someone help, i'm no dummy with engines but not really educated on "our" unique gm design just yet

 

[LookingforaGN]

PM'ED ya

 

[XLR8]

If FP is set at 52 "line-off" (which seems high) it should be much higher under boost. FP should rise pound for pound with boost so 52# FP + 19# boost = 71# FP. It sounds as though your fuel pump may be on its way out. Do you get any KR when the car pops?

 

[LITLV6]

i will sometimes get a lil knock when it pops. i dont believe mine has KR. i have a caspers gauge. thats how i see knock. i dont know that i have ever seen KR show up on the scanmaster. with vac line back on the fuel is at 42lbs. when i go wot it will climb to 52 until higher in boost and then drops below 40, around 38lbs seems to be when it pops out. Is this purely a fuel volume issue that my factory pump cant keep up?

 

[GNVYUS 1]

You have 90k on the stock pump and have been running it at a 52psi base pressure, it's F'd and your gauge is showing it.

You're seeing a manifold backfire when the popping occurs and the boost gauge flutters like that.

Many will recommend a Walbro, but those do what your stock ones doing so upgrade once and leave it, Denso 280.

And which chip maker recommends 52psi base pressure with their chip?

 

[pincugra]

You have 90k on the stock pump and have been running it at a 52psi base pressure, it's F'd and your gauge is showing it.

You're seeing a manifold backfire when the popping occurs and the boost gauge flutters like that.

Many will recommend a Walbro, but those do what your stock ones doing so upgrade once and leave it, Denso 280.

And which chip maker recommends 52psi base pressure with their chip?

How great your info is!But Can you give some more sample questions and answers.I really want to get more info about this topicIt really useful for me. Thanks.

 

[XLR8]

Is this purely a fuel volume issue that my factory pump cant keep up?

Correct, your factory pump was barely acceptable 20+ years ago at 13# of boost. You NEED a new fuel pump and hot-wire for it. If it were me, I wouldn't drive the car again until I had a new fuel pump.

 

[LITLV6]

noone recommended it. i was actually trying to compensate for the pressure dropping off. my thought process was if the problem only started when it dropped that low then maybe setting the base higher it would help a little. apparently i was wrong lol

So, i'm wondering...... i was thinkin about doin a walbro pump and hotwire kit, doing siemens 60lb. injectors and new injector wiring. does everyone recommend a blow off valve of a certain brand? what are the pros and cons of the blow off other than loosing all boost on the turbo when you let off the throttle? is the factory release enough, or is it bad on the top end of the engine? thanks for all the help guys this is very helpful.

 

[LITLV6]

oh and "gnvyus 1" whats the pros and cons of the walbro 340 vs. the denso 280 pump? a lil help here if you dont mind. is the denso direct replacement or do you have to get creative to make it work?

 

[2QUICK2B6]

you can buy the 60lb injectors and the best chip with adjustability and your fuel pump and hotwire from the same place ERIC at turbotweak

TurboTweak Home

 

[LITLV6]

you can buy the 60lb injectors and the best chip with adjustability and your fuel pump and hotwire from the same place ERIC at turbotweak

TurboTweak Home

thats exactly what i was thinkin. it seems as if everyone likes eric "turbotweak.com" pretty well. his sight shows he's out of the 60lb. injectors right now though. is he good at getting them to you pronto anyway? is there any other things i should be doin now?

 

[berserker6]

read read read. thats what you should be doing. as ive been told. and its true. get a little knowledge so your not going in "blindfolded":biggrin:

 

[yullose]

The other problem is... when you set base fuel pressure so high, it makes it that much more difficult on the pump when at max boost. 52psi + 20 = 72psi needed from the pump...

If you had set the base @ 43psi, then added 20psi, your pump would only need to push 63psi at max boost.

Follow what I'm saying ?

Obviously you need a new pump and hotwire kit... but the moral of my story is... add fuel via the chip, instead of fuel pressure. You can get away with lower fuel pressure if the injectors are open longer.

 

[LITLV6]

thanks for the tip. that makes sense, it never occured to me that you would add fuel and boost together for the required total pressure or (volume) from the pump. im gpnna order a pump and hotwire kit for sure now

 

[yullose]

Another thing to remember is... always unplug / re-plug the orange ECM wire whenever you make changes to the car... Especially fuel pressure changes. The ECM needs to relearn with the new adjustments to run properly.

Also as an FYI... some injectors will lock-up if you run too much base fuel pressure. Don't ask me how I know this.

If I were you, I'd get a new pump and hotwire kit installed... I'd reset the base fuel pressure to 43psi with the vacuum line off... and I'd reset the ECM by unplugging the orange power wire. If the car has a tip-in stumble @ 43psi... then bump it up another pound or two... but try not to go over 46psi if possible.
If the car still wants more fuel... then add it via the chip adjustment.

That should put you back on track.

 

[jasjamz]

Let's not forget the fuel filter...:biggrin:

 

[LITLV6]

Another thing to remember is... always unplug / re-plug the orange ECM wire whenever you make changes to the car... Especially fuel pressure changes. The ECM needs to relearn with the new adjustments to run properly.

Also as an FYI... some injectors will lock-up if you run too much base fuel pressure. Don't ask me how I know this.

If I were you, I'd get a new pump and hotwire kit installed... I'd reset the base fuel pressure to 43psi with the vacuum line off... and I'd reset the ECM by unplugging the orange power wire. If the car has a tip-in stumble @ 43psi... then bump it up another pound or two... but try not to go over 46psi if possible.
If the car still wants more fuel... then add it via the chip adjustment.

That should put you back on track.

good lookin out! thanks for the tip, i actually let that slip the mind as i was kinda annoyed when the little gremlin hiccup came back. and jasjamz i'll do a filter too

 

[bmackinnon]

Another thing to remember is... always unplug / re-plug the orange ECM wire whenever you make changes to the car... Especially fuel pressure changes. The ECM needs to relearn with the new adjustments to run properly.

Not that it's a big deal either way, but that's BS (for a simple base fuel pressure change)... the computer will immediately begin compensating to the new numbers without a reset, and will probably get there faster without a reset, because it's already learned in, and closer than the default/initial tables in the chip.... just sayin'..

And litlv6, not sure it was clearly stated, but with our turbo cars, the fuel pressure MUST RISE EXACTLY 1:1 with boost.... that's, a 1 lb increase in fp for every 1 lb boost.... it must rise and must be verified to rise.... your previously described 'dipping' fuel pressure is an absolute signal of a failing/inadequate fuel pump.... do not get on the car until this issue is fixed, or you will be changing head gaskets along with the pump....

 

[GNVYUS 1]

I'm not sure if Eric sells the Denso pump but he sells the Racetronix Denso 280 upgraded wiring kit that adds 5% more volume to that pump.

What's the difference between the two pumps, quality. One has damaged more GN's than any other performance item I can think of since a Cam issue years ago and another item has a proven track record of over 15 years and still going strong on MANY platforms.

Do a search on the Denso 280 thread, easy install with minor mods needed.

 

[yullose]

Not that it's a big deal either way, but that's BS (for a simple base fuel pressure change)... the computer will immediately begin compensating to the new numbers without a reset, and will probably get there faster without a reset, because it's already learned in, and closer than the default/initial tables in the chip.... just sayin'..

Well, that's the first time i've heard of this.

If anyone else wants to chime in, I'd sure like a 2nd or 3rd opinion... as everything i've read in the past indicates otherwise. I think even Eric Marshal suggests an ECM reset.

It would be nice to know for sure one way or the other... since I have a battery cutoff switch in the back of my car and I'd like to know how it affects the ECM/tune every time the switch is flipped off/on.