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stroker TBI minor problem

crazy427

crazy427

1/2 ton status
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Mar 10, 2003
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Edison , NJ
Ok here is the rundown I have a
383 stroker,
9.5-1 compression,
F.I. compatible cam,
dart iron eagle heads,
edlebrock tbi intake
670 tbi with a spaced stock injectorpod
venom hp 88lbs injectors & vacuum ref.Fuel pressure reg
stock distributor, performance module and MSD coil
Long tube headers/dual flowmaster exhuast
02 sensor is in the collector
and a custom burned chip

Now Here is the problem. When i start it up cold it backfires thru the exhuast for the 1st 30 seconds to 1 min of running. after that it is fine.
NO check engine light
No codes
With the scaner hooked up when it is acting up , all the sensors are working properly <temp sensor with in range alon withall the others.
Fuel trim is good
fuel pressure is good
timing has been set from 0deg to 4 deg, Runs the best at 2 deg but does the backfire thing no matter what.

It isnt running rick or lean and after that 1st miniate it runs like a F%^&ing Animal.

HELP!!! im at my wits end, I even call the place that burned the chip and they never heard of anytihng like thisand couldnt steer my in any direction except to brin the truck to there shop in oregon i believe.. /forums/images/graemlins/screwy.giflong hual frion Jersey.
 
is it the standard 02 sensor?? if it is I bet you need to upgrade to a heated O2. It takes a few minutes for the O2 to heat up being at the end of the header
 
/forums/images/graemlins/thinking.gifthe 1st person to make sense.. how do i go about doin this....
 
I'd like to know how as well. I've heard people say it before when problems arose, I am puting headers on my burb and want to install one as well.
 
i used to have my o2 further down the pipe where ti was more acessable. i would get lean codes everyonce in a while but no real backfireing. now with the new setup i got new headers and the collector with the o2 bung welded in so it is actually closer. but again i have got any code for anything at all
 
How many wires does you current O2 sensor have ? IF it only has 1 then it's not heated. If it has more that that (3 probably) then its heated. Make sure you are getting voltage down there when the truck is running as to heat up the sensor.
Blake
 
mine only has 1 wire it is a new o2 and it is working properly. how do you convert to a 3 wire heated o2?
 
I'm guessing the high idle/warm up or whatever is just different with the new motor/chip so the non heated O2 sensor and the new setup is the problem. Thats my guess anyway. Reminded me I need to get a 3 wire O2 for my Burb.
 
To get a 3 wire O2, simply go to the store, ask for a universal O2 for a '95 C1500 or something with a 350.

Then wire one to the computer for the reading, and for the other two, one to +ign and one to ground and you're done.
 
Cold startup isn't looking at the O2. Not sure how fast heated O2's get "up to temp", but 1-2 minutes might be pushing it.

I know nothing of how the TBI systems handle cold start.

MAF TPI starts by checking engine temp. Older setups used a 9th injector with a temp sensor to handle cold start. Later, GM got wise, and just increased the pulsewidth(?) of the injectors when the engine was cold. So...if TBI is similar, it would seem that the cold start programming in yours is dumping too much fuel for cold start.

Custom burned chip is for all of the mods you had done, or have you done more since having it burned?

If O2 wasn't getting hot enough for long enough, I believe you'd be throwing a code. At idle it WILL sometimes drop out of closed loop because of the O2 sensor cooling off, but that is "normal", just not optimum. Not going to hurt anything, just not bing controlled by the O2 sensor for that time.

You can watch the O2 sensor when you first start the engine, if its working right the voltage will climb as the engine heats up, level off, and start bouncing back and forth between low and high.
 
all the mods were done prevously, except for the location of the o2 sensor in the exhuast. i have watched the o2 sensor on cold start and starts out open the goes to closed then cycles back and forth. /forums/images/graemlins/confused.gifgoin /forums/images/graemlins/crazy.gif
 
Cylcles back and forth between open and closed, or just cycles back and forth between rich/lean?

If it's going open/closed often, then there is likely an issue with either the O2 sensor getting too cold, or something else.
 
ok at idle when acting up:
block intergrator--128
block learn-- 131
tps--.96
map vacuum---13lbs
o2 --- open loop and lean
after less than 1 miniate o2 switches to rich
abd when i bring up the rpms to 1500 it goes closed

I belive the o2 is working properly. it backfires the entire cycle of the o2.
Now get this --- while it is acting up if i go to functional tests in my scanner and kick on the back-up fuel& spark , it smooths out, runs good , no backfiring and seems to have more power. /forums/images/graemlins/screwy.gif
unfortunatly i cannot select between fuel and spark to test them individually /forums/images/graemlins/doah.gifalso i cannot find what the perimiters for back testing.
 
Was that chip truely custom, or just another off the shelf "performance" chip burnt from the specs that you sent them? To burn a true custom chip takes a LOT of time and $$$.

Sounds like you are running to rich durring the cold start cycle. This is a problem that I am having with mine since adding a 760cfm Holley TBI Popping in the exhaust till the cat starts towarm up). This is caused by unburnt fuel accumulating in the converter and igniting. Once the cat gets hot enough to keep the fuel burnt it stopps. Another possible cause may be that the temp sensor (the one for the computer) isn't reading correctly.

I've done some chip tuning and am pleased with the result, but still have a ways to go. To further tune my chip, I'm going to have go into the BIN and tweak my cold start cycle.

I would advise going over to thirdgen.org and start asking a few questions. A word of warning, those guys on the DIY PROM board are SERIOUSLY dedicated to burning your thier chips and some of thier answers will directly reflect that.

Keep asking and let them you know that you are trying to learn how everything functions before you start burning your own and you will get some straight answers.
 
Alldata and my scanner tell me that the tps voltage should be .9 to 1 volt at idle and 4 volts at wot. was .95 volts with my old 350 and always ran great.
A TPI engine should be around .5 volts at idle
 
Huh. '88 Camaro TBI says .5v as well, thought everything GM was that. Approx. 5 volts is WOT.

Camaro isn't a truck, but I'd just doublecheck in a truck service manual, or see if anyone here has the actual GM spec.

The higher the voltage, the more the computer thinks the throttle is open. May or may not matter, but it can cause some symptoms if it's wrong.
 
As far as I'm aware your ecu works off of preset values until water/engine temp gets to a certain value then it'll start taking info from your O2, MAP etc and start adjusting the fuel accordingly. So all your problems are when the ecu is not even using its sensors.
Are you sure your plugs are ok and valve clearance is good?
 
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