Long time lurker, first time (i think) writer:
'87 Chevy Blazer, 350, AT
Keep noticing that when i push down the accelerator in park/neutral, that it
starts 'lugging down', loping, missing, or something to that effect. Will
almost die, but seems to catch and keep on. At WOT, things seem to be ok,
and I do notice when accelerating i sometimes get a smooth/smoother surge of
power when flooring it. ....
Driving me nuts.
Did the tune-up thing with new plugs, wires, cap/rotor. Changed the fuel
filter. Changed the ignition module (gm),and knock sensor because i got
codes, but still does it. Does not seem to matter if warm/cold. Had timing
checked, multiple times.
Motor is a relatively new gm crate motor with 20k on it. No codes showin'...
The egr valve seems to move ok, at least when i have pushed on the diaphragm
when cold. Wondering if injector/s could be plugged, the cat plugged, or
something with fuel pressure regulator,or O2 sensor. Whats this sound like
to y'all??? Any ideas?
Thank ya much,
ps: Doc, from all the readin' i do on this NG, you seem to be one of the
wiz -kids. I am hoping you see this! :)
I'd like to know why you got WOT in neutral/park?
Take of your air cleaner cover and see if you have a pretty spray of
gasoline coming from the injectors.
Cat would cause constant lack of power IMHO....
O2 sensor should throw a code...
Any black smoke when it happens? It still sounds like EGR even though you
said it looks good.
Wiz kid I ain't, but I'll take a stab at it. I need to know exactly what
codes you pulled and under what driving conditions you got the codes. I'm
guessing code 43 right?
1. What's coming out of the tailpipe? Blue, black or white smoke?
2. What's yer' fuel economy like? You should be seeing about 15MPG with a
3. Pull a plug and look at it. Is it black and sooty, orangish/whitish,
electrodes melted at all?
4. What is your engine vacuum at hot idle? Get the motor to misbehave by
goosing the throttle in park/netutral, what does the vacuum do?
5. When timing was checked, was the EST wire UNPLUGGED? What is the timing
Doc and KJ:
You are right, a code 43 when knock sensor replaced (was driving to the
mountains, gave gas going up hill to try to keep up with I-80 traffic). When
code 42 popped up, I was cruising on freeway (60mph or so) -changed ignition
module, per Haynes manual.
1. fuel economy-honestly have not checked it lately... was 'round 12-13mpg
(combined) last year. It is not that good because I do alot of in-town
2. After driving for 1/2 hour or more, then stopping, I will get a whiff of
a strange smell, not really rotten eggs, but almost 'chemical', if that
makes any dang sense. my local neighborhood garage states that my cat will
get really hot and start to almost "glow".
3. Plugs just changed (12/31/03). the previous ones were considered normal
by all whom I had check-me, Haynes manual, dad, an auto-minded buddy, and
my local neighborhood garage, worn but normal, no oil or carbon on 'em,
lightish brown. Pretty clean, pleasantly surprised. Regapped, and kept 'em
4. Have not checked vacuum, will have to do that.
5. EST wire WAS unplugged when timing was checked.
KJ- I was not clear on WOT, sorry 'bout that. I only performed WOT while
getting on the freeway, not in Park!
-Fuel is exiting in a similar fashion (spraying down) from both
injectors -from what my ignorant ass can see...
-no smoke of any kind. burning hot exhaust out of pipe. kinda strong fumes.
Also, I forgot to mention in my original post that I did have it checked at
my neighborhood garage (early Jan.) and they put it on a real-time scanner
(?) and said I needed to replace my temp sensor( on intake manifold). So
that is another sensor replaced. Minor reduction in part-throttle lugging
for a short time, but was still there..always.
AND, to top it off, TODAY, I got a code 45 while sitting in my truck, idling
in park ,for maybe 5 minutes. o2 sensor/rich condition, so KJ, you are
right, the 02 sensor just threw a code! I think even my dumbass may be
seeing a pattern here:
code 43 - replaced knock sensor 11/03 -cleared code
code 42- replaced ignition module 12/03 -cleared code
code unknown- coolant temp sensor replaced by shop 1/03 (t-stat is a 195
degree unit from Napa)
code 45- tellin' me to replace the damn o2 sensor 1/27/04 @ 5:15 pm - have
not replaced, yet.
I am throwing away money chasin' this gremlin! Well, does any of this info
help?? I appreciate any clues/hints very, very much.
Thank you, and thank you for respondin',
Time for a beer...
I'd replace the cat. If your auto-minded buddy has a shop you might be
able to (temporarily) replace it with a piece of striaght pipe. Not
that you couldn't do it other wise, but it's cold soggy and generally
not nice out. That way you can test to see if it stops without
throwing more money at it. I know what you mean though, I HATE
throwing money at a problem. I wanna find it, fix it, and be DONE.
If I'm not mistaken when a cat clogs/fails it will restrict flow and
heat up ALOT. In severe cases it can sound like a bearing on a
belt-driven accessory. (due to exhaust gases excaping anywhere they
can) Try the truck with out/ with a new cat and see if your problem
I believe Doc's O2 regimine is every 5 years or 25k miles. If within
that, I'd clear the code and try the cat fix first. If after that,
personally I'd clear the code and try the cat fix first and see if the
code came back, but that's just because I'm cheap and lazy.
BTW if I'm not mistaken the code for a colant sensor is 14&15, one is
voltage too high and one is voltage too low (short). That is if it's
the OBDI system...
Disclaimor: Make sure to check with DOC about all I've said. Probably
wont surprize me if he responds directly too me telling me what a
retard I am.
If it's the original, it's gunna be a bitch to get off, but it's the only
way to remove the catalytic from the list of possibilities. He said the cat
was running hot, that is caused from one of two things: overly rich mixture,
or plugged up cat. The fact that he got an 02 rich code today suggests the
Good idea, but I'd troubleshoot the EFI system before I started ripping rust
old exhaust parts off.
5 years, 75K miles.
Oh c'mon now, I'm not that bad....................
True. Now that I've thrown many things at cars because of codes I always
clear them a few times before doing anything. Alot of times it just
dissapears... Fuel system would be a better choice.
Now that you say it I would have to agree. I also didn't remember that they
ran hot when they are rich. It sounded like it would solely be a cat problem
Well, I was right in 1 respect. You did tell me why I'm wrong. I guess I
could have said it a little differently. :-)
ICM's go out pretty frequently on these things, doesn't suprise me. KS's
usually last forever.
Still sounds about right.
BINGO. You're running super rich or she's plugged up. Have some goose the
throttle while you're standing at the ass end of the truck and look for
smoke then. Have someone tail you in another car and try to load her up
(part throttle going up hill, not enough to drop a gear) then floor it and
see if you get a blast of black crud out the back end.
Vacuum will tell us quite a bit. If you buy a mity-vac vacuum pump you get
a vacuum gauge and a vacuum pump in one.
By the time it gets to the ass end it will be warm, but shouldn't be burning
How old is the 02 sensor? If it's older than 5-years, 75K miles, it needs
to be replaced anyways. On your truck it's a single wire, non-heated
sensor, runs about $25.
Doc and KJ
Well, I cant thank you enough for the input. I am going to check it out this
weekend and look into one of those mity-vac vacuum pumps, I would like to
have one of them anyway...
I am busy until Saturday, and will get back to y'all and let you know what
I got to thinkin, when I first had the 'knock sensor' code come up, I
stopped by the nearest gas station, popped in a couple bottles of octane
booster/fuel system cleaner. Then i topped off the tank with Premium. Then
when i got home, i did it again. I m thinking i coulda knocked some crud
loose that is plugging somethin' up, or somehow damaged the cat...?
Thank ya again for the good info.
A few of the octane boosters that have been around for ages <can't remember
the name right now..................dammit> will chew the hell outta the 02
sensor<s>. There are a few products who combuistion byproducts don't play
nice with the catalyst in the convertor. There are far and few between, as
pretty much anything on the shelf now is EFI/emissions safe.
Well thats good to know i probably did not hurt it with the additives.I
normally dont use them. Can they hurt 02 sensors? I do remember the first
one was basically alcohol. I do remember when you had to check to make sure
it was ok, it could not have been that long ago, could it?! Im only 35!
I did end up dumping some other intake cleaners, such as 'Sea Foam' , so i
was thinking it got broke up some carbon that is causing this....
I will change the 02 sensor this weekend , just because i do not know how
it is and let y'all know. Any brand preference here??
Well, i took it in to ANOTHER neighborhood shop, and this is what they wrote
Found ECM commanding full egr at throttle openings just off idle-normal
condition. Vacuum leak at rear of intake manifold may be contributing to
condition. Recommend replace intake manifold gasket set. Egr diaphragm
leaking vacuum recommend replace egr valve.
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