Deb

I have read many of the posts about engine tap and knock when the engine is cold. Most of these posts describe the sound as dissipating after the engine warms up. My '01 MN6 seems to do just the opposite. I don't notice this soft interrmittent knock which (seems to be coming from the engine) until the engine is warmed up---usually 30-40 minutes into a one hour trip on the interstate at 75mph in 6th gear. I occasionally get a little bit of engine clatter if I drop down into 5th gear and crank it up. I always use 93 octane and have tried several different brands with no improvement. I really didn't notice this until summer (NCM delivery 9/23/00)---not sure if high ambient temps are a factor or not. Any ideas???

team-zr1

Have you checked for any PCM error codes such as multi misfires or knocks ?

Sounds like once the engine has gotten up to temperature your running a bit lean.
Any chance of getting a PCM trace to see exactly what is going on and send it to me ?

John

Fox

Had mine do the same thing on the way to BG in June. Only on longer trips, usually with A/C on coolant between 195-205, knocks on accelleration and going up hills. Had it to 2 different dealers and it shows no codes, they said that they can't duplicate it. DUH! I use only 93 octane gas and vary brands.

Deb

Thanks for the replies. How does one go about checking PCM codes?

BOBSZ06

Using the DIC:
1. Press Reset....Hold Options
2. Press Fuel 4 times within 10 seconds.
The DIC will go thru the various stages of codes automatically.
Wait until done and then manual use options to go forward; trip to go back.
For each stage use Gages to go forward; Fuel to go back.
Erase code: press reset
Press E/M to get out.

eagle_lex

ditto! I have a '99 six speed only use 93 octane have 13K miles and my car runs like total poopie after about an hour on the interstate at a speed of between 65 and 85 cruising. engine sputters (i guess it may be knocking), fuel economy drops from 32mpg to 7 or 8mpg and a BIG loss in power. sometimes the check engine will flash sometimes it will just stay on and sometimes it will go out. sometimes the car will smooth out on its own but usually after it cools down. had it to the dealer and they say it stored a code telling them that it had a misfire in the #5 cylinder. they are completely baffeled. they cant replicate the problem so they dont know what to tell me. i even inquired about trading me for a new one that actually is dependable and they are looking into that but for now i need some help from you guys!

team-zr1

Almost every C5 that i have looked at PCM recording of engine while it was being driven showed too lean of a condition that causes, knock, misfires, low engine timing, and of course lousy performance.

The long term wise decision is to own a PCM scanner/monitor, they are only about 300 bucks and run off your laptop computer while your driving and records all the engine functions the PCM moitors.

With a monitor/scanner tool ( I recommend the Ease enhanced powertain scanner) you now can lokk into the engine mangement and know exactly how your engine is functioning and performing.

A cheaper way to tune out issue like being too lean is a MAF translator, which takes 2 minutes to install and allows you to adjust what the PCM reads and tune out issues like ping/knock, misfires, timing and fuel/air ratios.
I have tuned over a dozen C5s in the last month and all regained good performance, much lower knock, raised WOT timing, adjusted air/fuel and overall the engine performs much better.

John

eagle_lex

where do i get a MAF translator? will octan boost help my problem? the dealer that i bought the car from says that they are willing to come and get the car and take it to there shop 150 miles round trip. should i let them do that? the dealer here in lexington can not fix the problem so either i fix it myself or let the other dealer come and get it. i just want it to run like it should. ps i have no mods what so ever. thanks again for your time.

intel55

Yeah check the codes and write all of the down history or current. Check your plug wires and coolant level. An ATAP would shed a ton of light on the situation. check your oil to see if it is getting past the rings. Look at the plugs to see if they are fouled.

:cheers:

c4c5specialist

Hi Deb,
Maybe you have an issue along the lines of what John said.
Please remember that your engine calibration is given as lean as possible for engine control emission standards. This situation could become worse, based on a number of factors.
If I were you, I would speak to your local dealership, explain to them the situation. My feeling is that there may be a revised calibration, or computer program for your vehicle. There may be other issues here, however, this is always the first course of action when diagnosing a drivability condition, to check for a reprogram.
You may need further diagnosis, but I would try this first, before you drive yourself crazy, try the simple fix.
Please keep us posted, and we will help if we can, c4c5

OPEN PLZ

My car does the same sort of thing when a plug wire comes loose or burns. I have had a constant burn problem for a good year plus. The car will miss most noticably after it gets up to 180* and do so the worst on WOT at 1500 to 2000 rpms. After about 2200 rpms the condition becomes less noticable. I only got a code once, I had a toasted wire #5 and had to have the car flat bedded 200 miles from S of chicago to effingham. If it is a plug wire and it has been going on for a while check your plugs, they will mostlikely be fouled.

Hope this helps

Greg :cheers:

Fox

Thanks to all who provided the valuable and knowledgeable information above. Just to clarify, I am not referring to a miss I am talking about spark knock. I have a Powerloader on mine. Is there a possibility that Steve Cole could address this with a programming tweak on my Powerloader. I would really like to eliminate this condition. :confused: :confused:

I would spring the $300 for a PCM scanner, but I don't have a laptop.

team-zr1

IMHO, you should not have ping with custom PCM code but your not the first one having ping ( too lean conditions) including my '99 that also has that powerloader code.
Yes they should tune that out but make sure they do not richen it too much where pings are gone but reduced overall timing.

As for a PCM scanner, you could spend about 50 bucks at like radio shack and get a D/C to A.C converter and use a regular P/C in the car until you could find a cheapo laptop.

John :bs

goldman

It does sound like something that could likely be "tweaked" with the Powerloader, especially if it's a lean fuel mixture problem which is a common cause of spark plug knock/ping...

I recently called TTS with a question about mine & Steve was easily available by phone to discuss my questions & offered some suggestions as well as offering to "tweak" the program if his other suggestions didn't help.

BTW..Make sure he is aware of any other mods or changes that could affect the program.

Fox

Thanks guys, I guess that I'll try to give Steve a call.

SDVette

One more thing for you to consider:

Do you live in an area that mixes alcohol into the gasoline during summer months for smog control?

Fox

The fuel is oxygenated year round here, but as far as I know there is no alcohol.

eagle_lex

well, gm picked up my '99 today and i told them about the problem that some of us are having approx. 1 hour into a trip. they said that their next "plan of attack" is to put a "black box" on the car and see what the engine is actually doing. i found the car to be storing 6 dic codes but most of them were the same code. i didnt write them down as i was in a hurry but im sure gm can figure them out. if gm doesnt find what is wrong and they tell me,"bring it back if it does it again," what do you guys suggest my next step should be? i already called the "whine line" (customer service) and opened a case and they told me to call them back when the dealer gave me my car back and tell them how it went. Please help!!!

eagle_lex

P.S.
does anyone know if this would fall under the lemon law and how would i go about looking into that. this is the third time i have had the car in for this problem, and the last two times i was told, " bring it back if it does it again." "it is storing a code of a mis fire in the #5 cylinder but it looked ok, we cant fix it if it isnt doing it now." that is a weak excuse if you ask me!

eagle_lex

third time and still GM says we cant duplicate the problem. they drove the car over 100 miles and no sign of the problem. they said that the only option they have now is to put a black box on it and give it back to me. the code that it is storing is 082. HElp!