Huge Power Loss! Need Help...

[Danspeed1]

I looked through a lot of other threads and I already see where i am headed with this; looks like I will be throwing parts at the problem until its fixed... Hopefully somebody can help direct me in the right direction. I will try and describe the problem as best as possible.

My 1995 Monte Carlo Z34 has 208K miles on it. It was running pretty decently for the most part until Saturday. I always missed a little if you jumped on it from a dead stop, and really never built power until about 2500 RPM's.... then it would move like a bat out of hell.

I went to the gas station the other day. Car was fine before I filled up with 89 octane, shell. Got 3 miles up the road and the sound of the engine began to change. It actually got much louder and deep. Seconds later it felt like the car was being held back. About 3 more miles down the road it barely had enough power to get past 60mph at part throttle. From a dead stop it barely moves. Takes a LOOOONG time to get up to speed. At cruise, I will give it 60% throttle to keep it going. Abruptly it will just struggle and begin to slow down, then after a while it may decide to slightly speed up. Here is the kicker. If I am moving at 60 and I punch it it will slowly get its power back as it raises up in the RPM band. At 6000+ RPMs it actually feels like its got its power back. This lasts until the 7000RPM shift, then it falls right back on its face, knocks, pings, is loud, and struggles back to the 5500-6000 RPM range where it gets its power back.

It's got a check engine light and I have no way of checking it... its OBD 1.5 with an obd1 port and an obd2 system... and its the two wire plug.

Where do I begin....

P.S. ran the car out of gas, and refueled with 93 from a different gas station, + octane boost, absolutely no difference.

Dan

[z34phoenix]

my first guess would be clogged cat converter...
my second guess would be bad vac leak. check the vac lines to the fuel pressure reg and the pcv system. how do your brakes feel?

i would also pull the battery cable and let it sit for a few hours to let the system reset and erase the code... then see if it comes back.

[robertisaar]

you SHOULD be able to go to any autozone and have them check it...

BTW: its not an OBD2 system. it might use a few P codes from the obd2 requirements, but thats it, they're just names. that is the only similarity it has with obd2.

[heavymtl]

i had a 96 grand prix se that had similar issues....however mine was knocking...it got worse....when i tore the engine down i found that i had a lifter that was turned...it was riding on the cam at a twist....it was so messed up that you could not even pull it from the block....i would get power at times...and other times have almost NO POWER...so possibly bad lifter..or lifters?


mine was the 3100 sfi engine

[jmgtp]

We are all throwing guesses out... so mine would be a possible slipped timing belt or a severe ignition problem (dead coil perhaps).

[Danspeed1]

I thought it was possibly the cat also, but it's still "exhausting" (stuff coming out of the pipes) Any creative ideas on checking the cat out?

My guesses were (1) bad coil pack, (2) bad fuel injector

Timing belt, tensioners, and pullies are new... installed just 8K miles ago....

I just don't see it being a lifter... there are no metallic sounds...

I have an OBDI port, with a 2 wire hookup. I have been everywhere (for a previous problem), and nobody had the tool.

Dan

[3400-95-Modified]

Car will still exhaust with a plugged cat, it will just be greatly restricted.

You can try shaking the exhaust back and forth to see if the cat has a rattling sound...

But other than that the only way to be 100% sure is just chop it off... I did that under a hunch I had a clogged one and this is what I found.

Back side


Front side

[robertisaar]

^ i've never seen the inside of an ungutted cat until now

also, where are you located? i have a ADS for tunerpro to read the datastream, and if there is a member close to you with an ALDL cable, then you can figure out whats going on...

[Danspeed1]

Can anybody say straight pipe...


Thanks for the advice so far guys,

I am located in Orange County, New York

I will take a closer look at the car today and post if there are any findings.

It would be great if I could read those codes!

Thanks,

Dan

[3400-95-Modified]

Can anyone say bleeding ear drums? Straight pipe is Obnoxious... Maybe its my old age and living in a neighborhood now I feel that I should run a full cat and decent muffler on the street...

[robertisaar]

Can anyone say bleeding ear drums? Straight pipe is Obnoxious... Maybe its my old age and living in a neighborhood now I feel that I should run a full cat and decent muffler on the street...

we like it loud, GRANDPA!

I SAID: WE LIKE IT LOUD GRANDPA!!!!

[Danspeed1]

Ok,

I took a look at the car today.

Disconnected the MAF sensor,... no change
Ran the car before closed loop to test O2 sensor,... no change
TPS sensor unplugged,... no change
Pulled spark plugs... plugs are "rust colored," they were replaced about 8K miles ago... they are not rusty; rust colored is the best way to describe the color.
Tested the coil packs by using an HEI spark tester. All the wires i pulled had a nice strong spark.
Banged on the cat with a hammer... sounds solid inside (I am skeptical about just cutting it off.


Took the car out for another ride. This is the best way to describe it.

If you floor it from a dead stop it sputters, and bogs like crazy, slowly taking off. This lasts all the way till about 4000RPMs. At 4K Rpms it begins to attempt to smooth out and you feel a little power returing and the car picking up speed. By 5000RPM's it begins to scream as it normally does and it feels like all the power is back. Feels exactly like it did before the problem occurs. When it hits the next gear, it bogs back down, the engine gets loud, and it feels like its holding back. It takes a long time to get to 4000RPMs again where it begins to pull harder.

WTF?


If its not getting fuel, it wouldn't make it to 4000RPM
If the cat is clogged, it wouldn't be able to breath at 4000RPMS, again not able to make any power.... am I on the right track...?

HELP

Dan

[robertisaar]

maybe its either WAY too rich or too lean in the low RPM ranges... disconnecting the MAF would make it go MUCH richer, and since it didn't make any change... i would have to say its getting too much fuel somewhere...

[Danspeed1]

Well I think I may have ruled out a couple more things...

I tested the coil packs and they are pumping out strong spark in all RPM ranges (wasn't able to check under load obviously).

I also did a vacuum test which came to around 18vac which is excellent. Had the cat been plugged, it is my understanding that back pressure would build, and my vacuum would slowly decrease from 18, and possibly even build pressure.

So this leaves us with (1)... sensors????? and (2) fuel system.

Am I forgetting anything?

Is it possible that the fuel pump is not building enough pressure or too much pressure at low RPM's? How do you check fuel pressure on this car?

What does my spark plug color (rust color) indicate?

Thanks for the help guys?


Dan

[robertisaar]

i don't know where the schrader valve is on a 3.4 fuel rail... but that is where you would test fuel pressure...

the "rust" color alone is normal. are there any deposits built up on it anywhere and what color are they? and are the electrodes looking completely normal or are they looking somewhat melted, or chipped or do they have little specks of metal on them?

is the rust color consistent all the way up the insulator?