dizwiz24

I need some help here. I have hotcam kit, Ed Wright chip, and long tube headers. My headers did not come with EGR or AIR provisions so I blocked off the port for them on the back of the intake with the block off plate.

My engine is knocking bad around 1000 to 3000 RPM (mostly around 2000 RPM).

I hooked up my scan tool and it is showing awfully high spark advance (levels I have never seen before) of up to 43 degrees at 2000 RPM! with slight throttle.

I don't know why putting on headers would do this so I am assuming it has to do with the fact I disconnected AIR and EGR, most likely the EGR...
I left the connector open, and plugged the vacuum line to it (the emissions unit by the ASR, whethers its EGR or AIR I can't remember).

Does anyone here have any ideas?

Nathan, did you run into this problem of getting knock when you put your long tube headers on?

Marcho Polo

in this thread there is an article about EGR function.

EGR helps to cool the combustion chamber down below 2500 degrees. If you disable EGR, then detonation can be a result. Some camshaft overlaps can be such that exhaust is pulled back in the intake with an EGR like effect.... I think the LT4 is like this.

I'm experiencing the same thing on my '90. I should have my new EGR valve today and see if the pinging goes away. 43 degrees timing at part throttle is normal programming in almost every stock chip I've seen.


To reduce the pinging, you'll need to cool the combustion chamber somehow.... either get the EGR working again, or change cams.... or??? Someone else might have an idea....


Good luck.

Nathan Plemons

When I installed my headers I actually removed my AIR pump completely. Come to find out that Ed Wright programmed it to the off position when I got his chip originally, or it's tuned to just not set a code if it's not there. The stock chip will still throw a code.

Anyway, I had the Ed Wright chip when I had stock exhaust and I've never had him touch it again. Installing the headers didn't give me any of the troubles you describe. I don't have a scan tool of any type or any data logging software so I can't get that much info for you. Sorry man, sounds like a real bummer. I don't know anything about timing but 43 degrees just sounds like it would be enough to cause a problem.

You might call Ed Wright and see what he thinks.

Nathan Plemons

The LT4 Hot Cam is supposed to have enough overlap so it's not needed. Remember the cam was designed for the LT4 which didn't even have EGR from the factory.

Too many people are running this combo for it to be a common problem.

However, showing my ignorance on the timing issue, 43 degrees which sounds a lot to me is prefectly normal according to somebody who actually programs chips. :smash: Show's you how my experience is lacking in that regard huh?

Marcho Polo

I knew the LT4 didn't have EGR and I remembered hearing that the cam design is what let's it get away with it... cool!

Now, 43 degrees at Part Throttle is not uncommon, but at WOT that is much lower. I've seen an Ed Wright chip for an '85 with iron heads have as much as 52 degrees timing at very light throttle.... I've never done one that high though....

PeteL

AIR and EGR are two seperate functions. This problem has nothing to due with AIR.

Sound like too much knock just for EGR removal, how much knock retard are you getting? What are knock counts?

I would be looking more for a lean mixture or timing problem of some sort at this point. You sure it's real knock and not something mechanical?

Good Luck,

Pete

Nathan Plemons

They serve 2 functions correct, but they all share the same plumbing.

PeteL

EGR and AIR share plumbing? don't think so! :D

Nathan Plemons

Somebody have a top down detail picture of the engine? I was looking through my old pictures but they aren't bright enough in the areas that we need to highlight this.



All of these are tied together which go to the EGR and the AIR pump. Now there might be check valves and such in there, but it all goes into the same assembly of tubing and hoses, in which case it comes out as a unit when removing it completely.

L98 might be different.


[Modified by Nathan Plemons, 3:35 PM 10/2/2002]

89vette

During crusie and light throttle, timing is high like that. My car at crusie is 42 degrees. EGR can prevent detonation and pinging. It could be that you need to disable the EGR in the chip.

Jason

PeteL

Hmmm, I need an LT1. EGR could tee off exhaust manifold to get exhaust gasses at same tubing as AIR I guess. Simply conveyance of location for exhaust gas source.

All kidding aside, the functions are not inter-related.

AIR - air injection reaction: supplies air (oxygen) to complete combustion of unburned exhaust gasses when engine is cool (also aids in heating up the cold catalytic converter, and in some cases provides a source of O2 to the catalytic converter)

EGR provides a source of exhaust gas (cooler than combustion chamber gas) which contains very low levels of oxygen to reduce combustion chamber temperatures during a very limited range of RPM and engine load to help reduce the formation oxides of nitrogen. Because of this cooling/pressure lowering effect the timing can be advanced to offset any reduction of power that may or may not be felt at partial throttle (why you can get knock with EGR removed if programming is not changed to accomondate).

Nathan Plemons

Yup. I knew they served completely different functions, but I did know that they use the same plumbing, on the LT1 anyway. I thought it kinda strange myself. Learn something new every day huh?

:cheers:

As for the problem at hand though I still don't understand it. The Hot Cam should have enough overlap to eliminate the need for EGR. Lots of people run this combination. I even know a few people who run this same combo without any programming and it doesn't cause any knock. Very strange indeed.

65Z01

True that lack of EGR will raise combustion temps that could cause ping, but you may lessen it by turning up your AFPR a little to richen the charge.

Of course you can always have the EGR provision added into the headers if necessary, right.

The air should only go into the header tubes during warmup to bring the O2 sensor up to operating temp. Later the air is diverted into the cat.

Also, with a knock sensor operating properly the ECM should pull timing so you don't hear ping. You might verify that the connection is in tact because you should be able to see the knock counts and pulled timing on the scan tool.



[Modified by 65Z01, 4:03 PM 10/2/2002]

dizwiz24

I called Ed Wright and they said that I need to have my chip upgraded. They need to disable the EGR, disable AIR, and richen the A/F slightly to compensate for the hotcam.

BTW....I had (before the install) and still have a Code 43 Electronic Spark Control Unit Failure (what is says in my scan tool).

My scan tool detects no knock retard at the start of this pinging (which sounds like a rattle/vibration, etc.) so I am assuming the COde 43 means they are malfunctioning....

Hopefully I can get this all sorted out

dizwiz24

BTW the upgrade from fast chip is going to cost me $150!!!!! and a few days down time

dizwiz24

Ok, all of you guys who have engines that don't knock after installing long tube headers....it must really really be great....to not have an engine that knocks.....grrrrr.hisss. :cry

Sent my chip back to Ed Wright. Hopefully he will disable the EGR functions, and do whatever else he needs to to get this thing straightened out.

old salt

did you remove the cats when you installed the headers? or were they gone before.i have worked on many autos that had a wrist pin knock. but until you freed up the exhaust you couldn't hear it. the backpressure would keep the pin from slapping around. once we put a modified exh. like headers. and removed a clogged cat then the wrist pin noise was unbeleiveable. hope this makes sense , it has been a long day and i can't formulate the words to ...nevermind i'll just go to bed..best of luck