Engine is a ZZ4TPI, Edelbrock intake/SLP runners/ported plenum. SVO 24lb injectors, stock 48mmtb. New TPS and MAP sensor. All other sensors appear to be working properly on my autoxray. In the morning or at various times the car starts and runs very rough. These are the symptoms on the scanner:
Desired Idle 925rpm
BLM 128
Open Loop
Spark Adv 18 deg
Idle Air Mtr position 40 steps
Injector pulse 2.4ms and higher up to 3.7 at idle.
MAP 1.80 volts.
Learned Idle 59 steps.
If I step on the gas in this condition, the pulse climbs to 3.4 4.4 6.6 etc. Climbs with just a slight blip of the throttle.
The injectors are just dumping fuel.
Now...When the car decides to run properly, here are the readings:
Inj Pulse 1.7ms
O2 cross counts climb from 0-254
Map 1.72 volts
Learned IAC Pos 57 steps
TPS .54
Fuel Pump voltage 12.6
BLM 108
Spark Adv 14.7 deg
Idle air mtr position 0 steps
The idle will stay high for a few moments when the car goes "normal" Idle about 1200rpm then the Idle air mtr postion goes from like 33 down to 4. I stop the motor, restart and idle air mtr position goes to 0.
CTS and MAT sensor appear to be working fine.
WHen I blip the throttle at idle or in drive, the injector pulse width barely climps over 2.0. Something is telling the injectors to dump fuel. Could this be a lazy IAC, allowing too much air and causing the engine to dump fuel to compensate. Of note, Since the ZZ4 TPI conversion the car has always had a closed loop BLM of 108, thats with a stock L98 chip and the Street and Performance Chip. My stock L98 chip has the egr function off, fans on a little sooner, and 24lb injectors instead of 22lb. The car has ran perfect with both chips before. I have two computers and she does the same on both. The problem seems to abate now once the car warms up or after multiple stops and restarts.
Any ideas?
p.s. No Codes. Fuel pressure has been varied between 38 and 50 with no affect.

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Rob P
89RSconvtZZ4TPI Edelbrock Intake
SLP Dual Cold Air Intake 1 5/8" Headers Semi-Siamesed Runners, IROC
suspension, alum shaft. Numerous mods.
92Z28convt5spd (stock)
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

[This message has been edited by Rob P (edited November 01, 2001).]

 

If your BLM is 108, then you are pig rich while in open-loop. The computer is using your tables and no map input, dumping fuel.

I'd recommend chip tuning to adjust your fuel injector constant. You definitely need some tuning.

 

do me a favour, and check your tps voltage at wide open throttle.. Let me know what it says. MIne was 1.4Volts at WOT, which is bad.. it was trhe computer in my car. But it could be the tps, or maybe even a wire going to the computer from your tps

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1988 Pontiac Trans Am GTA L98 5.7L, Black on Black with 114,000kms.
Custom 3" Stainless Exhaust Y-Pipe back (High flow Cat and Flowmaster Mufler)

 

I'm no expert, in fact I don't even play one on TV, but the IAC stepping to "0" could indicate a vacuum leak somewhere, which is affecting the MAP reading and having the ECM think you're accelerating.

 

Did you bypass the throttle body coolant (IAC)? My car runs a little rough until it warms up since I bypassed the coolant.

 

Hey... heres a way to check for leaks... get some TB cleaner from the dealer... spray it around vacuum hoses and intake gaskets and wait to hear if the idle changes.
Have you pulled the IAC valve?



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1988 Pontiac Trans Am GTA L98 5.7L, Black on Black with 114,000kms.

Best ET 14.559 @ 95.25MPH
Custom 3" Stainless Exhaust Y-Pipe back (High flow Cat and Flowmaster Mufler)

 

hey Hey Rob, How's the O2 Sensor looking is it stuck lean or lazy lean.

Or there may be a problem with the Iac, It maybe bad, Showing one thing, doing something else, pull it out and check the passage for a bunch of carbon.

The O2 sensor being lazy will cause it to go into open loop and not throw a code.

my .02

 

Rob, i think your car has the shizo-phrenic-heebie-jeebies. I suggest you loan it to me next summer and i'll take it by a bishop i know for an exorcism. Whaddya think?

 

You know, PK has a point though. A lazy O2 sensro could do weird stuff right at that threshold before closed loop and drag the computer into doing weirdness. And they are goofy sensors.
I suggest trying that, and if PKs right i'm buying him a beer cuz that was a good one.

 

Okay, the O2 sensor seems fine. When the problem is present she is bouncing from like 30 to 800mv. When in closed loop steady driving, around 560-650mv range.
I know the 108 BLM means the car is running rich but when it acts up, the BLM is 128! Supposedly perfect. The car runs great at a BLM of 108. I agree I need to do some chip tuning. As the engine drops into closed loop BLM goes from 128 to like 114 then to the steady 108 she seems to like.
As I analyze this more it seems to be related to engine temp. This morning I let is set and warm up before going to work. Car ran fine. I also noticed on my autoxray that after the car set all day in a nice breeze the start up CTS temp was 109 deg! No way! Car ran around 154 deg on the way home (80 deg outside) and when It hit around 165 deg it smoothed out and ran perfect.
Also to review, the car runs great in closed loop/BLM of 108. The problem is when cold, BLM is perfect 128 but the injectors are dumping fuel.
Guess I'll get some starter fluid and check for leaks. If not I'm leaning towards a goofy CTS.
Ed, you're right, she does have the
shizo-phrenic-heebie-jeebies!

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Rob P
89RSconvtZZ4TPI Edelbrock Intake
SLP Dual Cold Air Intake 1 5/8" Headers Semi-Siamesed Runners, IROC
suspension, alum shaft. Numerous mods.
92Z28convt5spd (stock)
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

robp,
idle postition low meaning air is entering
to survive idle request.
if lowering the fuel pressure doent effect
idle BLM, O2 is questionable. i installed
24# stock chip and had to lower pressure to
arrive 128 BLM. was also 108.
do you have a totally stock chip?
moving the injector from 22 to 24# leans
mixture. so if the injector rate is 24 the
22 should blow 90's. if not, O2 and recheck.
airdeano

 

Rob,
I had the same problem with mine. After looking at the IAC and replacing it because it was not working. I then replaced both temp. sensors. The one in the coolant and the plenum, I have not had a problem with mine since.

 

I just put in an AC Delco O2 sensor this February. I really hate to just keep replacing sensors with no result. I just sprung for over $100 on the TPS and MAP (only two parts stores in town, NAPA and DAP). The CTS was also replaced in Feb.
The BLM stays at 108 wether I lower fuel pressure to 35 or raise it to 50. That's on a stock L98 chip and my Street and Performance ZZ4TPI chip. Thanks for the ideas, keep them coming. I really would hate to cry uncle and send this thing to the dealership.


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Rob P
89RSconvtZZ4TPI Edelbrock Intake
SLP Dual Cold Air Intake 1 5/8" Headers Semi-Siamesed Runners, IROC
suspension, alum shaft. Numerous mods.
92Z28convt5spd (stock)
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

My car ran irradically untill it warmed up, it was because of a faulty temp sensor for the ECM.

12 bucks & no problems since.

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G O D BLESS AMERICA

http://www.3rdgenformula.com

87 Formula 5.1 TPI Auto Modified (Yellow/Black)
87 Formula TPI (5 Speed) Yellow/Gray STOCK
14.8sec 1967 Buick Riviera
1990 Buick Riviera
83 Camaro
83 T/A

 

Not to harp on it, but when it's doing this stuff what's the O2s Crosscounts, if it's working right your not going to be able to read it with a dmm it just gives you an average.

if the o2 sensor's crosscouning less than 2x it could be the route of the problem, it heats up when driving, and stays hot for a bit, but when it's good and cold, and in the headers it may be real lazy, and be fine on the highway

 

Again, PK has a point. You'd really need a scope or at least be reading the x-counts to get a picture of what the O2 was doing. When semi-warm/cold it could be 'fluttering' around stoich, making the BLM seem perfect to the ECM no matter what the mix is doing. It sounds crazy but O2s are half black magic really, even try an el-cheapo one if it'll make you feel better about the constant sensor replacement.

 

When cold, the O2 sensor is moving from like a low 34 to a high of 700mv. Then when the car is warm it steadies out around 560-600mv.
Does this help?

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Rob P
89RSconvtZZ4TPI Edelbrock Intake
SLP Dual Cold Air Intake 1 5/8" Headers Semi-Siamesed Runners, IROC
suspension, alum shaft. Numerous mods.
92Z28convt5spd (stock)
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

Yeah, the O2 sensor should never 'steady out' under any circumstances in closed loop. It should have a very pronounced swing, the exact magnitude (it's at least a few hundred mV, maybe 5-600 as a WAG) evades me off the top of my head but i'll look at some diacom i have saved when i get home.
Basically, it sounds like you're describing what i just said. Your O2 sensor is crazy and is just putting out a voltage based on it's mood more than the actual reading. I would definitely swap it if this was my car doing it.
Look at it this way. You MUST have a bad sesor since 2 ECMs have done this. Since you've observed the illogical increase in PW around the closed/open loop transition, something is making the ECM think it needs more fuel. Since the MAP is new and apparently reading fine that one is out. The CTS could be suspect if perhaps it has a 'cold' spot in it's resistace curve fooling the ECM into thinking that the coolant temp suddenly dropped, sending it back into cold start enrichment. Or the O2 could be flaky, making the ECM think it can't make cross counts, and thus the ECM keeps adding fuel trying to get the x-counts.
Or it could just have schizo-phrenic-heebie-jeebies

 

Here is my plan. Tomorrow I pull the TB off my 92 Z28. Even though I put a new TPS on the ZZ4TPI, I can check and see if perhaps the IAC is going wacky because the 92 tb runs perfect. If that does not work I get the can of starter fluid and check for vacuum leaks. If that reveals nothing then it's time for a new O2 sensor. If that doesn't work it must be the schizo-phrenic-heebie-jeebies


------------------
Rob P
89RSconvtZZ4TPI Edelbrock Intake
SLP Dual Cold Air Intake 1 5/8" Headers Semi-Siamesed Runners, IROC
suspension, alum shaft. Numerous mods.
92Z28convt5spd (stock)
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

I would double check that your timing displayed on the scanner is the same as being displayed by a dial back timing light. I would also use a vacuum gage to see if the readings concur with the MAP.

I had a bad pick-up coil that sported some of the same problems-mainly the appearance of a lazy O2 sensor. Noticed that the timing went to hell and the vacuum from 16 down to 5 (both at idle) when this happened. -Matt-

 

To add to this, a good mechanic of mine suggested that since I have an old EGR valve just mounted to the intake, it may be leaking even though I have a nipple blocking the valve. He said the spring can get weak and lift allowing an exhaust leak, and screwing up the MAP sensor. Guess I'll put a block off plate and see what happens, then contine with all the great ideas you guys have presented.


------------------
Rob P
89RSconvtZZ4TPI Edelbrock Intake
SLP Dual Cold Air Intake 1 5/8" Headers Semi-Siamesed Runners, IROC
suspension, alum shaft. Numerous mods.
92Z28convt5spd (stock)
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

try a heated O2 sensor,when your at idle it is not getting hot enough and that could be why it is lazy,under more load it will get hotter and work better(should get to like 600* I believe)

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89 FORMULA 350,WS6 SUSPENSION,HOTCHKIS STB,KONI REDS,WONDERBAR,SLP REAR CONTROL ARMS/PANHARD,POLY BUSHINGS,FRESH 355 MOTOR,TCI 12" STREETFIGHTER,TRANSGO SHIFT KIT,3.70 GEARS,FLOWMASTER EXHAUAST,SLP 1 3/4 HEADERS,NO CATS,58 MM BBK,MINIRAM INTAKE,COLD AIR,ALL FREE MODS