Get ready for a rather long one, folks. It's kinda drawn out, but I really need help with this one, so please bear with me.

Well, my car's been acting really weird lately, running like total crap when cold. I mean I can't even drive it until it warms up because the engine won't hold a smooth idle below 1800 rpm. If I try to hold the rpms at around 1400 or so when it's cold the engine seems to stutter. I mean all cylinders are firing but it's rough as hell, like they're all out of whack or something. The engine also needs lots of pedal movement to produce the same rpms it would when at operating temperature. If I try driving it while it's still cold, the engine will stutter and seems to have no power, until I stab the gas pedal. The only way the engine will make enoguh power to move the car is if I have the gas pedal pressed like nearly halfway. It'll run fine once the rpms are above 1800-2000 but I don't like revving it that high while it's still cold.

All these symptoms disappear nearly completely once the motor hits a certain temperature (can't tell exactly how many degrees because my temp gauge is inaccurate) warms up but the engine still won't respond instantly to throttle input. A quick stab at the gas pedal makes the motor bog bigtime. Same thing happens if I try WOT acceleration from a standstill. The motor seems to bog and the car takes off without any wheelspin. Where are the notorious thridgen traction problems everybody talk about? Surely, the motor is bogging and not putting enough power to the rear wheels.

I know the bogging is due in part to the air filters, but it's still there without them. I've done the timing, IAC and TPS adjustment routine several times but the stuttering and bogging just won't go away. The cold stuttering had nearly disappeared after replacing the plugs, wires, cap and rotor about 8 months ago but now it's just as bad as it was before. I was able to minimize the bogging by playing around with the TPS position with the engine running. It's happiest at 0.57 volts.

I thought all this might have been the fault of a bad oxygen sensor so one day with the engine cold I disconnected the sensor and started it up and guess what? No SES light and absolutely no change in the stuttering. Then I started the motor again at operating temperature with the oxyegn sensor disconnected and yet again there was no change at all. The SES light didn't even blink. I checked for codes, and sure enough, nothing came up.

Can somebody please tell me what the hell might be going on with this freakin' POS. Why won't it run right? EFI gurus, work your magic.

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'88 IROC 305 TPI
Crappy 700R4 slushbox
Gutted airboxes
180 degree T-stat
Advanced base TPS voltage
Relocated IAT sensor
Momo steering wheel (gotta luv it)
Ram-air setup coming soon
Flowmaster muffler (puke)
Taylor SpiroPro wires
Accel cap and rotor
Ported plenum
Kills: '94 Z28, Olds Aurora V8, bunch of Mustangs, T-birds, ricers, and others who assumed a 12 year-old car would be too slow.

 

when you checked your codes did you get a Code 12?

if you don't, your ECM is toast

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Webmaster: www.IROC-Z.org

 

Yea if you got the normal 12's from the ECM it should be working, if you didn't i would neccassarily say its "toast". You could also have an SES light burned out.

Brendan

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1987 IROC-Z L98,SuperRam,EB 6085's,LPE 219/219 Roller, Crane 1.6RR, EB TPI Base, 58mm TB, ADS 24#, AFPR, K&N, EB TES, Catco Cat, 3" Borla Cat-Back, Accel cap,rotor,distro/other crap, MSD 6AL, MSD Blaster 3, Aluminum DS, 94 Disk Rear, Adjustable Valve, Precision 3.73 Gears, Sub-Frame Connectors, Hotchkis Lower Control Arms, KYB Shocks/Struts, Suspension Techniques Lowering Springs, Polyurethan Bushings all over the place, Moog Upper/Lower Ball joints and Tie Rods ends/Idler Arm,

To see the ROC, Check out the webpage Here

 

If you disconnected the O2 sensor and got no codes that would tell me you have a burned out SES light bulb. I'd try that first. Does the SES light come on momentarily when you first start your car.

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Formerly known as 1984L69Z28

1984 Z28 - L69 optioned, 350HO w/ Trick Flow Heads, Drop Forged Lunati Crank, Crane Cam and 1.5 Roller Rockers, Stock Z28 Intake Manifold, Highly Tweaked Rochester Carb(700cfm), K&N Filter, ThermoMaster Chip w/ 160 Stat, Comp Headers, 3" Stainless Dual Exhaust w/ no Cat & Dynoflow Muffler, 4 wheel disc brakes, etc....

God bless us father, son, and holy ghost....whoever goes the fastest wins the most!!

 

Yes, I do get a code 12 when I check for codes and SES light does work fine. The SES light also 'bounces' (flashes once) when I turn the ignition on like it's supposed to. So that means that the ECM is OK, unless the ECM itself was sometime replaced with another unit that doesn't belong in this car. But that's a long shot.

I reset the IAC and TPS today. The engine was previously idling at 450-500 rpm in Drive but I raised it slightly to idle at around 550-600 rpm. I get a lot better throttle response with the slighty higher idle. The TPS is at 0.57 volts where the engine likes it most. The strange thing is that while I was setting the TPS and checking for how much the engine bogs at which setting, a sudden stab at the gas pedal produced some pretty bad backfire through the intake. It would never do this in cold weather. In fact, the bogging was barely noticeable then. Now, since the temperature has gone up here, these problems are coming back to haunt me again.

I was told several times to check the MAT sensor and CTS, since the problems are temperature related, but they both checked out fine. They gave me identical readings too at the same temperature. Another thing - the motor doesn't bog when cold like it does when it's hot. I mean a quick stab at the gas pedal doesn't make it stumble, only slight throttle manipulation does.

What's the matter with it? Is it possessed? Am I gonna have to get it exorcised ? Jeez,this @#$%ing car is driving me crazy !!!!!

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'88 IROC 305 TPI
Crappy 700R4 slushbox
Gutted airboxes
180 degree T-stat
Advanced base TPS voltage
Relocated IAT sensor
Momo steering wheel (gotta luv it)
Ram-air setup coming soon
Flowmaster muffler (puke)
Taylor SpiroPro wires
Accel cap and rotor
Ported plenum
Kills: '94 Z28, Olds Aurora V8, bunch of Mustangs, T-birds, ricers, and others who assumed a 12 year-old car would be too slow.

 

Just because the SES is flashing does NOT mean that the ECM is OK. It could still be bad, although I'm not necessarily saying that's what your problem is, just don't rule it out. ECMs go bad all sorts of different ways, and you don't always get a code for it. Yeah, you should check the CTS circuit. Also I would check the ignition module since backfiring out the intake means timing is too advanced. Besides the computer, the module is in charge of timing (along with knock sensor). You can take it to an auto parts store to get it tested for free. As for the O2 sensor, it doesn't start giving the computer info until the engine reaches a certain operating temp, and since you have the problem when the car is cold, you can rule out that possibility. Here's something to try. Insert the paperclip into the same place you usually do AFTER you start the car. By watching the SES light while the car is running, you can see if it is in open or closed loop, and if it is in closed loop if it is rich or lean. Here's how to interpret it: if you get two quick flashes every second, then the car is in open loop. Once it stops the quick double flashes, it is in closed loop. The light will go on and off intermittently. When it's on, the O2 is reading rich, when off, lean. How does this help? Well, you say that things seem to smooth out at a certain temp, then this way you can see if things smooth out exactly when the car goes into closed loop, or if it's at some random point/temp. If the problem is going away just when you go into closed loop, then the problem is probably fuel delivery related, meaning rich or poor condition which the computer can only compensate for once it is in closed loop and is aware of the problem.
Hope this wasn't too confusing.

 

can the ecm reset itself because mine seemed to erase a code placed in it this morning and shows clear of codes....

 

Hey Vicious, I've already tried checking for open/closed loop operation with the paper clip. The strange thing is that it didn't go into closed loop at all with the paper clip in place. I thought it would go into closed loop once it reached that temperature where the engine smoothes out, but it didn't. It stayed in open loop way past that temperature. I pulled the clip out and, IIRC, the idle slowed down a bit. I put the clip back in and now it was in closed loop this time. I tried this again several times over the next few days and the same thing happened. It's like the the clip prevents the ECM from switching to closed loop. Is that supposed to happen or not? I think it shouldn't otherwise how would anybody who tried this trick know when the ECM was hitting closed loop operation.

I wonder if autozone will let me try out a new ECM in my car?

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'88 IROC 305 TPI
Crappy 700R4 slushbox
Gutted airboxes
180 degree T-stat
Advanced base TPS voltage
Relocated IAT sensor
Momo steering wheel (gotta luv it)
Ram-air setup coming soon
Flowmaster muffler (puke)
Taylor SpiroPro wires
Accel cap and rotor
Ported plenum
Kills: '94 Z28, Olds Aurora V8, bunch of Mustangs, T-birds, ricers, and others who assumed a 12 year-old car would be too slow.

 

The CTS provides more input into how the car runs than you think. Mine was bad and giving me an extremely rich condition. Screwed all kinds of stuff up. If I remember the chip burners on the board say lots of values are determined from that one sensor.

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Rob P
89RSconvtZZ4TPI
Edelbrock Hi-Flow Intake
SLP Dual Cold Air Intake
1 5/8" Headers
Semi-Siamesed Runners
MSD6AL/relocated MAT/ AdjFPR/IROC frnt@rear swaybar/wonderbar/steeringbox/alum drvshaft/ Alston SFC/3:23posi disc rear/MAC LCA/H.Adams Panhard Rod/KYB struts/ shocks/
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

I checked both the CTS and the MAT sensor. The readings were within specs and also identical since they're basically the same sensor.

Originally posted by ViciousZ:
I set the static timing at 8* BTDC. I don't think that's too much since I've seen people running as much as 10* on stock TPI motors. I should add that after resetting the IAC and TPS, I get spark knock at startup. I can hear the motor knock once as soon as it fires
up but not after that. I tried WOT acceleration several times and I got no spark knock whatsoever.


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'88 IROC 305 TPI
Crappy 700R4 slushbox
Gutted airboxes
180 degree T-stat
Advanced base TPS voltage
Relocated IAT sensor
Momo steering wheel (gotta luv it)
Ram-air setup coming soon
Flowmaster muffler (puke)
Taylor SpiroPro wires
Accel cap and rotor
Ported plenum
Kills: '94 Z28, Olds Aurora V8, bunch of Mustangs, T-birds, ricers, and others who assumed a 12 year-old car would be too slow.

 

Wow....guys, this was a great thread. Very informative, no sarcasm, kindness. This is a "textbook" way that questions here should be answered. To those involved.....I applause you.
Alex

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Alex (A.K.A chevyboy) '91 RS 327c.i., ported, polished, & gasket matched heads & intake. Competition cams camshaft, trans-go shift kit(stage 3)> manual valve body, cat-delete, MSD (ignition, coil, 2-step, timing retard/ advance), T.C. lockup switch, Flowmaster exhaust, Edelbrock Pro-Flo open element, Edelbrock shocks, struts and lowering springs. CRAGAR drag wheels w/BFG T/A tires. Lowered 2.25" in front and 1.5" in rear....Best E/T 12.84 @109 mph. Newest mod= Nitrous Express adjustable nitrous kit. "I survive for your survival" -me- LT2 U.S.M.C. Demolition

 

oops.....I meant that for a diff. post.but this deserves it too

 

What I meant about the timing wasn't that your initial timing was screwed up, but that for some reason the computer was advancing the timing too much, either because it's busted, or because it's getting bad info from some sensor. I know the computer depends on a lot of sensors for it's timing advance. It has to know engine speed, temp, load, etc. But I'm really not sure how much it depends on the module. The thing is, the module is something you can check without having to guess, and it's pretty easy to take off. I have no idea why the paperclip trick didn't work for you. I've done it before and it worked OK. But my car only goes into closed loop when I'm out driving around. When I sit at idle, it goes back into open loop. Guess the exhaust gasses aren't hot enough at idle. Here's another idea, something noone has mentioned yet. What about the MAF???