Problem Under Boost! Any Help?

[grandprixgtp_91]

Ok here is my Problem

Last Summer the car ran Flawless, no studder, no miss, i could put boost to 7200rpm crisp and clean and bury the speedometer in no time.

Anyways i stored the car for the winter and just took it out last week, the car was fine in 1st and 2nd gear, but as soon as i got into 3rd WOT under boost, as soon as i hit 5000rpm it would studder and bog, then 6000rpm was fine till 7200rpm, and 4th gear was the same.

So i figured it was probably bad plugs.

the stock plugs are AC Delco R42LTSM and i put in Autolite AR94 plugs, so i figured id go a step colder and i just changed the plugs today using Autolite AR 93 plugs, set gap at .045"

well im guessing that the problem was definatly spark related, because now its way worse!!

it does it at 3000rpm now in 2nd gear and backfires and i cant even get to 5000 rpm.

is there a plug i should be using? gap i should set?

this obviously seems to be something with the spark plugs, but the wierd thing is, with the old plugs it was fine all last year, maybe its the colder weather, but i dont know.

i flipped on the wideband 02 today to see whats going on with these new plugs, its all normal , and when under boost it goes to about 11:1 afr until about 5-6 psi then it starts to chug and whatnot, it goes to 13-14:1 afr, i dunno whats going on, im hoping thats just the computer cutting fuel because of the chugging.

has anyone had this problem, any advice on plugs and gap, its 91 GTP with 3.4L DOHC personal experience is awesome for this kind of stuff!

Thanks in advance!!

Jake

[IsaacHayes]

Just wondering, but maybe the injectors are getting sticky from sitting... and or clogged... Just an idea...

[grandprixgtp_91]

Well they were brand new injectors last summer, 42.5lb/h and this problem got worse from changing the spark plugs. i think if they were sticky or clogged it would run bad all the time, and when the car was being stored i would go start it and let it run for 20 min once a week.

I sure hope the injectors arnt bad lol.

Jake

[IsaacHayes]

Ah, ok yeah if you started it up every now and then they should be fine.

The plugs may be too cold. So you are two steps colder than stock? What is stock gap? You may be going too cold. 5-6psi isn't a WHOLE lot of boost...

[grandprixgtp_91]

yeah thats about 2-3 steps colder than stock, and the stock gap is .045" which is what i gapped it to

i know 6 psi isnt much, but im going to turn it to 10-12 psi thats why i went with the colder plugs

Jake

[turboD]

You don't mention fuel. Is it the same fuel in the tank that you stored the car with ? Old fuel can cause all sorts of problems - the light hydrocarbons evaporate off leaving the heavy hydrocarbons - causes hesitation, poor flame travel thru the cylinder, poor cold driveability, etc. If you filled the tank with fuel after taking it out of storage, it could be a "Winter" blend of fuel causing the problem - higher amounts of alcohlol and other additives to help remove water from the fuel system. More alky in the fuel or higher oxygenated fuels will run leaner under load. One way to tell if the fuel has a high content of alky is to check the long term fuel trim. If it's higher than normal (over 5%), it's a good sign of alky or winter fuel. D

[grandprixgtp_91]

nah its got fresh fuel

Jake

[RedZMonte]

i run stock plain jane ngk plugs with stock gap. if it gets worse with colder plugs like mentioned they may be too cold. Im running 7psi w/o problems. could have been corrosion on the plugs from sitting... ditch the autolites, i hate them... they are for lawn mowers haha... NGK or Delco and run a .035 gap.. smaller gap doesn't blow out under boost as easy.

Also have you hooked up a fuel pressure gauge? plugged fuel filter? do you have a CEL? what computer are you running? My OBDII system tells me what hole has the miss fire and what not.. Bad plug wire, bad coil, bad O2?

I would defiantly start with a pressure gauge and go from there.. sounds like fuel to me. if your air fuel ratio leans out you arnt feeding enough fuel.. if it was lack of ignition i would think it would read rich because its not burning all the fuel...

the '91 didnt have a MAF, how are you reading the boost in the ECU? my MAP maxes at 0psi and my MAF adds fuel for boost. did you convert to MAF, running a FMU, convert to a 2bar map and tune....?

Keep us posted,
S

[grandprixgtp_91]

Hmmm, maybe i should throw in some stock Ac Delco R42LTSM plugs and see what happens, but i am worried about knock from the hotter plug, but ill definatly put the gap to .035" , i just dont want to use ngk plugs, i hate them.

Havent run a fuel pressure test, im running factory computer with TGP code, The wires are new, and so is the coils and ICM and O2 sensor. i think my problem is with the plugs, its just wierd how they worked fine, then started acting up.

Jake

[IsaacHayes]

The newer AC Delcos are NGK plugs... LOL

[RedZMonte]

i have never had a problem with NGK's on any of my boosted cars. IMHO i think NGK's are one of the best plugs if not the best.... Personal opinion... Alot of the 3800 s/c guys run Autolites but i personally think they are inferior....

I run stock heat range on mine with 7psi.

S

[grandprixgtp_91]

Well if NGk makes Delco plugs it must be the platinums or iridums because i dont think they make the copper ones.

Personally ive have nothing but bad luck with NGK plugs, and anything i own, lawnmowers,dirt bikes, snowmobiles, they seem to stop working very very fast,

In my 99 GTX with the 3800 s/c i use autolites with no problems.

im not trying to say NGK's are garbage its just they have left a bad impression on me from personal experience, I suppose id be willing to try them though,

Are you using copper ones? if so do you happen to know the spark plug number on them?

Thanks

Jake

[RedZMonte]

I don't remember off the top of my head, but they are the cheapy ass plain jane plugs.. i ran plain delco's for the longest time and only got NGK's because they didn't have the Delcos in stock at the time.. Honestly i have allways had great experience with NGK's and delcos. But like i said i have stock heat range plugs in mine and have never had any issues with it.. I have a OBDII conversion on my car and never have any kr issues.

S

[grandprixgtp_91]

alright, ill give it a try then, ill go with delcos to start, because i might have a set kickin around

thanks for the info.

Jake

[IsaacHayes]

The newer AC delco plugs which are iridium have NGK stamped on them.