List of Symptoms, no apparent cause

'95 Monte 3.4L DOHC, 250,000kms
Symptoms: 1. Lack of power. 2. Engine sputters during initial acceleration in the morning and after work. Throttle to the floor, car accelerates slowly then "comes alive" with
more power, but it's not all there. 3. Under wide open throttle, engine will not rev over 5500rpm so it won't make it to the shift point. Have to back off throttle to shift. 4. During cruising speed, 60, 90, 100, 110, 120km/h, engine "bucks". Feels like a miss, but not consistant. Only happens under load, back off the throttle and it's gone. Doesn't matter if TCC on or off, in 4th or 3rd, same thing but less apparent with increased engine speed. Mostly around the 2200 - 2700rpm range.
At WOT: -Knock retard is at about 10 and spark advance is at around 24 -Engine speed 4575rpm -Vehicle Speed 61mph -Throttle load axis is 99.96%, throttle position at 4.46 volts -In closed loop -TCC mode off, 251rpm slip -Trans temp 72C -Incoming air temp - 16.3C -I have other data, but not sure what's important in this case
Previously thinking clogged cat, check the temps as per Shep's instructions and got 57C before the cat and 97C after the cat. I wish I could post what the LT and ST fuel trim values were, but I haven't learned how to get that data yet. I also wish I could quickly check fuel pressure without paying a garage to do it. I am not sure if any of the values I posted are out of the ordinary, especially spark advance/retard. Just looking for some opinions on where to go. I'm thinking motor mount, the timing belt I still never got around to changing, something stupid like a bad ground or something deeper.
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Did these have a MAF or MAS sensor?
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MAF sensor
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Steve Mackie wrote:

MAF most definately from just this symptom alone. Like a sticky throttle on a carb. Also check the EGR valve if it has one.

HUH? 5500rpm is way high. I should want to shift if you let of the gas at about 2000 rpm.
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Apparently, the MAF is telling me about 0.6 grams/sec. The manually tells me 6.9 is normal. However, the RAW BYTE from the PCM is 153. The calculation I was told to use is "grams/sec=N/256" which mean the number could only be between 0 and 1.

Under WOT the shift point of this vehicle is around 6500rpm.
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Steve fuel trim readings would help, if it is lean due to low pump output or restricted filter this would reveal that, also the spark retard is high. There has been some evidence that a bad serpentine belts or tensioners can fool the knock sensor/pcm to retard the timing. Maf readings of 6gms at idle is ok. Why are you including the motor mount in your concerns here? Did this engine ever go to 6500 comfortably? When I was an Olds SM, I drove one of the first stick 3.4's and I found it to have poor low end torque, but you seem have have different symptoms. This sputter is the key here it seems, I assume the wires and plugs have been attended to. Again fuel trims are needed here to see if this is fuel related, also at that mileage a dedicated fuel injector cleaning is in order, whether related or not.

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There is a rattle coming from the engine in the 2000-3000rpm range. I will inspect closer today when I am replacing the timing belt. I have gone to 6500 quite comfortably in the past, it's only recently that I was unable to. The plug wires were replaced about a year ago, plugs about 2 months ago. I will see if I can get the fuel trim data.

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Well, this rattle could well be the reason for the timing retard, I would focus on that for now.

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I think, emphesis on THINK, the ST fuel trim is 0 and the LT fuel trim is +21 counts. Apparently 128 counts is 0%. The range is from 0 to 256 counts. I am guessing 256 being 100%, than +21 counts would be +16.4%. At idle it is -25 counts LT and -3 counts ST, or -19.5% and -2.3%.
Steve

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Well lt trim is really trying to pull fuel back, might want to clean the MAF with electrical parts cleaner when you do the tb. Finding this engine rattle is key here, you want to get that knock retard in line, which could affect fuel trims because of the effect of retarded timing on combustion efficiency. Look at the egr also when apart, make sure it is fully seating, not carboned up. Also check for the fuel press. reg leaking into the vacuum hose.

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I *think* the rattle is the A/C compressor brearing. Cheap part, $39, however you need $400,000,000 worth of tools to change it. The manual says it can be changed "on vehicle", but you still need the special pullers to get at the bearing. What am I going to do?
Just finished changing the timing belt, actually pretty easy job. I did it the "easy way" (thanks Ian), with no special tools and without removing the cam carrier covers. Got a little scared when the timing marks didn't exactly line up after seating the belt and tensioner, but it's not like it's out a tooth and the car runs fine.
Steve

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Took some more data when I got home today, all while idling.
The LT seems to be steady at -25 (-19.5%) counts at idle and -13 (-10%) counts at roughly 2000rpm. The ST is pretty flat, fluxuating up and down by only +/-2 counts. The MAF however appears to be fluxuating quite a bit. Holds steady for a while, but dips rapidly then bounces back up. There is no apparent change in engine sound or speed while this is happening.
Still searching for that rattle, starting to think it's a stupid heat shield now.
Steve

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Injector pulse width is below 2msec at idle and hovers around 1msec at 2000rpm. But really, it's all over the map, from 1 to 3 msec.
Steve

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Steve at a steady load/throttle, the maf should be pretty flat and the pulse width too, of course the o2 sensor is changing the pulse width slightly as required, pay attn to that fluctuating maf.

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I would like to clean the MAF as you suggested. Is just any electronic parts cleaner okay, how about WD40?

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Radio Shack one source, elec parts cleaner only, anything else leaves a film on the wire in the MAF.

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Have you unbolted the manifold to see if it runs better with out the exhaust? Then if it does your CAT is clogged...No sense in running around the car looking or making other problems....Do you even have a MAF code if not then dont worry about it......Checking temps is one way but you have to consider metal is a conductor of heat..Meaning even if air isnt fully flowin through the CAT some air is and the metal will still heat up....Best to just unbolt it at the manifold and if that dont work then go else wheres....Better to try the easiest first.. S Cook Re: List of Symptoms, no apparent cause Group: alt.autos.gm Date: Thu, May 26, 2005, 12:07pm (CDT+1) From: snipped-for-privacy@capital.net (Shep) Radio Shack one source, elec parts cleaner only, anything else leaves a film on the wire in the MAF.
'95 Monte 3.4L DOHC, 250,000kms Symptoms: 1. Lack of power. 2. Engine sputters during initial acceleration in the morning and after work. Throttle to the floor, car accelerates slowly then "comes alive" with more power, but it's not all there. 3. Under wide open throttle, engine will not rev over 5500rpm so it won't make it to the shift point. Have to back off throttle to shift. 4. During cruising speed, 60, 90, 100, 110, 120km/h, engine "bucks". Feels like a miss, but not consistant. Only happens under load, back off the throttle and it's gone. Doesn't matter if TCC on or off, in 4th or 3rd, same thing but less apparent with increased engine speed. Mostly around the 2200 - 2700rpm range. At WOT: -Knock retard is at about 10 and spark advance is at around 24 -Engine speed 4575rpm -Vehicle Speed 61mph -Throttle load axis is 99.96%, throttle position at 4.46 volts -In closed loop -TCC mode off, 251rpm slip -Trans temp 72C -Incoming air temp - 16.3C -I have other data, but not sure what's important in this case Previously thinking clogged cat, check the temps as per Shep's instructions and got 57C before the cat and 97C after the cat. I wish I could post what the LT and ST fuel trim values were, but I haven't learned how to get that data yet. I also wish I could quickly check fuel pressure without paying a garage to do it. I am not sure if any of the values I posted are out of the ordinary, especially spark advance/retard. Just looking for some opinions on where to go. I'm thinking motor mount, the timing belt I still never got around to changing, something stupid like a bad ground or something deeper. ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =----
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My 2002 monte was similar..
1. Lack of power 2. wouldnt go past 4500rpm, so it too wouldnt shift. 3. while trying to get it to shift, it backfired once, but I think the computer was shutting off some of the cylinders to keep it from hutring itself :)
Anyway, it is still under warrantee, and the dealer replaced the CAT! Runs like new now...
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