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Old 08-14-2003, 05:39 PM   #1
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cuts out at >1/2 throttle >190

SEE REF THREAD:
http://www.thirdgen.org/techbb2/show...hreadid=194914

for some reason i haven't been able to reply to this thread.

the plug wires only have like 3k on them, but i haven't replaced the coil. could it be the coolant temp sensor? makes sense that it wouldn't throw a code if the ECM just thought it was really cold or hot.

still doesn't make sense to me why it would only cut out above very light throttle. symptoms seem like something to do with timing...

ugh. i've been out of town, and i need to fix it this wknd. thanks all.
~Trace
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Old 08-15-2003, 12:05 PM   #2
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I see. I tried twice to reply, but got an error message each time. That thread is somehow FUBARed. I even closed (locked) the thread and re-opened it, but no dice. I get the same error message. Don't know why. I'll just close it and leave it up. Maybe it a friggin' worm...


Have you checked the MAP sensor output voltage at a known vacuum level?

A low MAP (high vacuum) can keep the mixture lean under load, causing backfire, hesitation, and overheating.

You might also want to test the TPS output voltage along the full range of the throttle travel (key on, engine off, of course).
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Old 08-15-2003, 12:24 PM   #3
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sweet, thanks Vader. i haven't checked those. are there charts in the Haynes manual for the TPS & MAP? if not, do you possibly have them handy?

i already have your coolant temp sensor resistance chart printed out, and gonna check that ASAP.

on an unrelated note, i think i'm going to be replacing this 3rd gen with a 96 Impala SS. do you still have your SSs? what year(s) are they? anything to look out for when shopping? i've heard of some probs with rearends, but otherwise they seem very solid. any forums as good as this one for those cars, besides impalassforum.com? thanks again!
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Old 08-15-2003, 01:40 PM   #4
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If I'm correct, the TPS on your car is non-adjustable. You should be able to read about 1.0VDC or less at the closed throttle position, so the ECM can interpret it as a closed throttle when the ingnition is first turned on. From that point, voltage should increase in a nearly linear fashion with increasing throttle opening. TPS output voltage should be at a minimum of 3.91VDC with the throttle wide open.

The MAP sensor output voltage should be proportional to absolute pressure, or inversely proportional to manifold vacuum. Of course, the hose connecting the sensor to the intake manifold needs to be intact, free from cracks, leaks, splits, or kinks. The electrical connector needs to be clean and tightly seated.

The MAP sensor can be checked with a vacuum source and a digital voltmeter. The sensor should output a 0-5VDC signal at the 'B' terminal. The output voltage is based on absolute pressure at the hose connection. The sensor should output full voltage (5.0VDC) when there is one BAR (barometer, or atmosphere) of pressure applied. This means there is basically no vacuum (0" Hg) and the Absolute Pressure is at 14.7 PSIA.

When the Absolute Pressure decreases (due to vacuum) the voltage output on the 'B' terminal should decrease as well. Test the sensor down to about 20" Hg of vacuum, or 0.33 BAR (4.9 PSIA), where the output voltage should be around 0.8-1.2 VDC. The voltage should vary in direct proportion to the Absolute Pressure, or amount of vacuum applied. If the MAP output "jumps" or "sticks" at a given point, the sensor bridge circuit or the mechanical diaphragm is failing. Since there is no good way to repair a MAP sensor, replacement would be indicated.

Click the image to open in full size.

Yes. A '94 and a '96. The Saginaw 10-bolt is a little light for the application once the engine starts making serious power. It's a heavy car to get moving.

OptiSparks are always suspect, but can be fixed pretty reasonably - the same as any other LT1/LT4.

Make sure it's a TRUE Impala and not a home-converted Caprice. A true Impala will have the RPO codes "WS7" and "Z09" on the label in the trunk lid. If not, it's a fake, and should be priced accordingly.

http://www.impalaclub.com/naisso/forum2002/default.asp
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Old 08-15-2003, 01:54 PM   #5
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awesome. out comes the vac pump & multimeter.... will post findings. thanks.
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Old 08-18-2003, 09:44 PM   #6
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>:-\

quick update & plea for more ideas...

i added an inline fuel pressure gage tee'd into the flex hose under the hood. checked the coolant temp sensor cold, and it read about 2 Kohms. started it up and getting a steady 10psi. i took it out and drove it until it started showing the symptoms again.

limped back to the house, it died in the driveway & wouldn't restart. popped the hood & watched the FP ga go up to 10 psi when the key was turned on, bleed down to 0 slowly, and then jump back to 10psi when cranking, but it wouldn't turn over. well, TG at least the fuel pump is not the problem again.

checked the coolant temp sensor while hot, and it read about 200 ohms. checked the voltage on both the TPS and MAP, and both would articulate 1V to 5V within their ranges & appeared OK.

i even took the plug off the CTS and jumped a 1 Kohm resistor into it to make the ECM think the engine was still cold, which did nothing to help.

i went out for a while, came back, and it had cooled down some. it fired right up & i pulled it back into the garage...

anyone have any more ideas? :lala:

also for Vader, how would you compare your 94 to the 96 SS? i really prefer the 96, and have a line on a black one at $12k. i think i could also pick up a burgundy 95 for about $9500. miles & condition on both are very similar. are the tach, OBDII, and floor shifter really worth $2500?? also on the codes, does it have to have both of those codes in the trunk, or just one or the other? the 96 i checked out had WS7, but not ZO9.

:hail: thanks everyone... Trace
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Old 08-19-2003, 07:13 AM   #7
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Spark module, distributor pickup coil, or spark coil.

RBob.
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Old 08-19-2003, 11:56 AM   #8
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thanks for your reply. i replaced the distributor 3k ago, including pickup coil & module. i bought a new coil last night & will install this evening....
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Old 08-19-2003, 10:46 PM   #9
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Dirty or bad AIC module maybe?
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Old 08-20-2003, 06:50 PM   #10
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well, i stuck the new coil in just now, went for a test drive, and i think it's even WORSE! started cutting out at an even lower temp, and died completely more abruptly. would've been stranded, but thought to throw my bike in the back. as said, the whole ignition system has 3K or less now.

AIC module? you mean IAC? (idle air control) the valve? or is there an associated module as well? i thought the ECM ran the IAC. how does one test the IAC?

thanks all... Trace
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Old 08-20-2003, 07:01 PM   #11
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Yeah, it is the IAC. Sorry, It was bed time when I was typing that Anyways, it is controlled by the computer, but it gets clogged up with black gunk and it will give an inaccurate reading. Pull off the TB, and then remove the IAC from the bottom of it. Carb or TB cleaner will work pretty good at cleaning it out.

Good luck,
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Old 08-20-2003, 07:06 PM   #12
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oops! I just realized that you have TBI and not TPI. I think the IAC is to the left of your TB in the manifold.

Take care
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Old 08-21-2003, 02:05 PM   #13
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ah, i thought it was on the TBI itself. does anyone have a pic of a TBI on the manifold with all the gizmos ballooned?

what about the fuel pres regulator? and which gizmo is that? possibly injectors clogged, but it seems the regulator could be more easily affected by temp.

i'm starting to think it's fuel delivery again. my FP ga is in the flex hose by the charcoal canister, so can't daignose anything past there.

thanks.
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Old 08-21-2003, 05:39 PM   #14
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I'm out of ideas for ya, but I'm really interested to see what it ends up being. Keep us updated

Matt
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Old 08-21-2003, 06:45 PM   #15
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When you did the ignition module did you use an AC Delco one or aftermarket? If if is the latter, replace it with AC Delco, aftermarkets are junk.
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Old 08-22-2003, 10:13 PM   #16
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well, Morley, RBob, & everyone else who suggested the ignition module had it right. i pulled the module out of my boat, stuck it in the car, and it's running like a top so far. i guess i just couldn't believe the brand new (crappy aftermarket) module would go bad already. :\ looks like the boat's getting a new DELCO module now!

thanks so much for all the help. Trace
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Old 08-23-2003, 01:51 AM   #17
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It really is a sad thing that after all these years of HEI (since 1973) no aftermarket company can equal the reliability of the AC Delco units.
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Old 08-23-2003, 01:51 AM
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