I am stumped over this.

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Feb 6, 2011 | 02:51 PM

Crowhater

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Drifting

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From: Montgomery Texas

I am stumped over this.

If I go full throttle from a dead stop the car starts missing and popping. We changed everything in the distributer and it still did it. Then we ran the car with it hooked up to the laptop and it did not throw any codes but it shows it is going to 62* of timing when it starts missing. So I changed the knock sensor to see if that was the issue but it is still doing it. Once I am going I can nail the gas and the car accelerates just fine, the car also drives fine. I checked fuel pressure and it is perfect also. What am I missing guys, this just started out of the blue. When I first start the car I can normally launch it once or twice before it starts having issues.

Feb 6, 2011 | 03:09 PM

corvette95

Melting Slicks

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From: Decatur, Alabama

injectors and or fuel pump?

Feb 6, 2011 | 03:10 PM

94z07fx3

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Similar issue on a different car was cured with fuel filter. It idled sweet as you want but didn't get enough gas at WOT.

BTW have you taped a FP gauge to the windscreen and checked FP under load?

Feb 6, 2011 | 03:19 PM

Bronze85

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From: Vernon Hills Ill

Have you looked at fuel trim/block learn numbers?

Feb 6, 2011 | 03:20 PM

Crowhater

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Drifting

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From: Montgomery Texas

Quote:

Originally Posted by 94z07fx3

Similar issue on a different car was cured with fuel filter. It idled sweet as you want but didn't get enough gas at WOT.

BTW have you taped a FP gauge to the windscreen and checked FP under load?

Yes we did put the fuel pressure gauge on the windshield. The car has new 24# injectors and the pressure is 51psi with the vacuum off the regulator. The fuel filter was changed 4 months ago.

The tach jumps around when the car is missing.

Feb 6, 2011 | 03:56 PM

94z07fx3

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TPS move smoothly from near zero to near +5 volts as you open the throttle?

Feb 6, 2011 | 04:03 PM

ex-x-fire

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Are you saying you get 62* of timing advance? That is too much, should be close to the low 40*s.
Is this an LT1 or L98?

Feb 6, 2011 | 04:05 PM

Crowhater

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Drifting

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From: Montgomery Texas

Quote:

Originally Posted by ex-x-fire

Are you saying you get 62* of timing advance? That is too much, should be close to the low 40*s.
Is this an LT1 or L98?

This is a L98 and yes the computer is telling us when the car is acting up that it is jumping to 62* of timing.

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Feb 6, 2011 | 04:28 PM

Sandpiper59

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From: Oliphant Ontario

If the tach is jumping around at the same time it sounds more like a bad module in the distributer or bad wiring to it. If the problem is far more common in first than higher gears, check the plugs and wiring harness to the distributer and at the fire wall (engine torques over on mounts more in 1rst than upper gears)

Feb 6, 2011 | 04:41 PM

#10

mseven

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Joined: Feb 2005

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From: The Motor City

Quote:

Originally Posted by Crowhater

it shows it is going to 62* of timing when it starts missing. So I changed the knock sensor to see if that was the issue but it is still doing it. Once I am going I can nail the gas and the car accelerates just fine, the car also drives fine.

If it is truely at 62* @WOT, you will need to look at the things that effect timing. Knock sensors, and fuel would have no effect on the timing moving as you've describe. Check initial timing (6*btdc), yank distributer (gear etc), timing chain and gears, (moving etc.), cam gear, or the like would be my first thoughts. Timimg at WOT (only) should ramp from about 25 @2400 rpm to around 30* above 4400 rpm.
What software are you using to scan with through your laptop?

Last edited by mseven; Feb 6, 2011 at 04:47 PM.

Feb 6, 2011 | 07:30 PM

#11

rob-cyn

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From: Orlando Florida

What year is the car. Mine was doing this and it was the ICM. I changed it out and all was good.Mine is a 94

Feb 6, 2011 | 07:35 PM

#12

Crowhater

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Drifting

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From: Montgomery Texas

Quote:

Originally Posted by rob-cyn

What year is the car. Mine was doing this and it was the ICM. I changed it out and all was good.Mine is a 94

The car is a 1990 with a ZZ4 crate engine. We changed the wire to the knock sensor and found that the computer chip was lose. After fixing this the car runs much better but it is still doind it every once in a while.

Feb 7, 2011 | 10:05 AM

#13

bjankuski

Safety Car

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From: Glenbeulah Wi

Check your ignition module, and power wire to your distributor.

Feb 7, 2011 | 10:29 AM

#14

pcolt94

Le Mans Master

Joined: Jan 2006

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From: Orlando FL

Quote:

Originally Posted by Crowhater

When I first start the car I can normally launch it once or twice before it starts having issues.

At this point the engine might be in open loop which would indicate a richer mixture from the tables. When it heats up it goes into closed loop and the A/F ratio comes from the O2 sensors. However during WOT I believe the O2s are out of the loop and it reverts back to the tables for WOT operation. I'm not sure if this concept might relate of not.

Quote:

Originally Posted by Crowhater

The tach jumps around when the car is missing.

This is a different thought process. I would check all connections to the ECM. Not sure where the tach signal is taken off on the 90, but I would look at that related circuit and any power and grounds that might feed related modules or components in those areas.

Feb 7, 2011 | 11:01 AM

#15

Crowhater

Thread Starter

Drifting

Joined: Aug 2010

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From: Montgomery Texas

The tach reads off the distributer. We checked all the grounds, and the Module has been changed. last night we found that the Prom chip was loose on the board and after we fixed this the problem seemed to go away. I can now do wide open launches with no problem. Two diffrent times the car has sputtered at 3/4 throttle but will clear up if I go full throttle. The lap top crashed so we were not able to run maping on the car yesterday. With any luck we will have the laptop up and running today and be able to tweak the program on the car.

Yesterday we bumped the initial timing to 11*BTDC it was set at 8*BTDC.

Once again this is a 1990 coupe
zz4 crate engine
700r4 trans
2800 stall
transgo shift kit
z pac clutches
long tube headers
holley throttle body
holley reg
24# fic injectors
PCM chip
new fuel pump
new filter
new distributer
307 gear

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