Hot Rod Forum banner

1 - 19 of 19 Posts

·
Registered
Joined
·
65 Posts
Discussion Starter #1
Any ideas?

I inherited a 2000 Silverado with a vortec 6 litre. Before receiving it, the exhaust was re-done and cats removed. The check engine system was disabled and cannot be read.

When the truck is cold and in gear, the idle jumps up and down, and will eventually die. The idle is fine in park or neutral. If I am in gear and driving I have no issues, and once it is warmed up I have no issues. the only time it presents itself is if it is cold, I am in gear and idle.

I thought I would get lucky by just replacing the likely culprits. I replaced the IAC valve and TPS sensor. I inspected and cleaned the MAF and EGR. Both looked fine. I also cleaned out the throttle body and intake the best I could with berrymans and seafoam.

I am a novice and will probably have to take it to a shop and have the check engine fixed and diagnosed.

Any suggestions would be appreciated!

Steve.
 

·
Not Considered a Senior Member
Joined
·
10,722 Posts
What's throwing me off here is "The check engine system was disabled and cannot be read"
I would think the first step of getting it fixed would be to repair the check engine system. Now, I'm not up to par on the computer system in your truck, but I can't say I ever heard of just disabling the check engine circuit without shutting down the rest of the system as well.
However, the issue your having is somewhat common on those year models. More than likely the intake gaskets are leaking. GM recommends using they're replacement gaskets that are upgraded thickness.
 

·
Banned
Joined
·
2,440 Posts
Get a can of carb cleaner And spary a little around the Throttle body base And where the intake manifold meets the heads if the idle goes up you have an air leak.
 

·
Registered
Joined
·
132 Posts
if not intake gaskets it could be a temperature sender/sensor. if the sender does not work the computer runs a default setting and adding fuel for a cold engine is not in the default settings. try your temp sender, or if not that maybe the computer itself is not compensating for the temperature mandated fuel needs. had this problem on my 99 tahoe 5.7. it was the temp sender/sensor.
 

·
Old(s) Fart
Joined
·
5,729 Posts
First of all, you cannot "disable" the "check engine system" on an OBD II system - it's integral to how the computer works. What was likely done is that the Check Engine light on the dash was disabled (ie, bulb removed) or something similar. Plug a diagnostic tool into the OBD II port and I guarantee you'll get a data stream out.

Of course, the first problem will be all the codes pertaining to the cats being gone...

Given how little restriction modern cats add, I continue to struggle with why people waste the time and money to do this.

Work through the codes and figure out what is going on.
 

·
Registered
Joined
·
65 Posts
Discussion Starter #7
I thoroughly sprayed carb cleaner around the intake and so no change in idle. Temp sensor did nothing. I had the auto parts store plug in the reader and it was dead.

I believe the overall idle is low as well. In park it idles at 500 - 600 RPM

Any other ideas???
 

·
Registered
Joined
·
2,403 Posts
obd 2

u just may want to ck with your DMV before u get carried away. in my state when u take it through inspection they plug in and take readings..when u last took any of your veh's in did they plug in ??? if your state does the same and your system ain't working??? your wasting your time if u don't get it to work, you will fail..
 

·
Administrator
Joined
·
8,211 Posts
Joe Padavano is correct in what he said here. If the scanner wont power up then someone clipped the 12 volt + wire in the OBDII ALDL pin #16. That will keep the scanner from powering up. The check engine bulb probably has been removed.
Be sure ALL the fuses are good .
You need to adress the engine / pcm communication problem first as you need that to read codes , live data and possibly to perform bi directional testing etc. in order to diagnose the problem correctly and quickly
Or you could spend a buttload of cash just throwing parts at it ,so you then can take it to a mechanic and complain you dont have any money to pay him to fix it.:rolleyes::rolleyes::rolleyes:
 

·
Registered
Joined
·
698 Posts
Something you might look at is the MAP sensor. I have a 2000 with a 4.3 that had probems with a seal around the sensor that would seem to get worse when it was cold, but sealed up once it got warmer and more pliable.
Not saying thats what it is, but you might squirt some thick oil around it to see if it makes any difference. If you pull it out you might see what I'm talking about as far as being loose.
I don't know about a 6L but I know I had intake gaskets that went bad because of the dexcool or whatever it was called coolant from the factory.
I also had to replace the central fuel injection with a multi port kit that got rid of the poppet valves. Don't know if thats on the 6L or not.
Your computer is working or it wouldn't run period as that is what turns on the fuel injectors, as well as the spark control I believe.
FWIW
ssmonty
 

·
Licenced Automotive Technician
Joined
·
1,625 Posts
Guys, we can't be throwing out "check/replace this" scenarios on this one. The OBDII has to be fixed, so he can get a starting point, or he could spend thousands on "maybe it's this". something the pcm is looking for is missing or out of range, and with OBDII, you need to see the data that the PCM is providing to accurately repair it. Get the scanner communication thing fixed, and get the codes and some of the data stream, and it will be much easier and less expensive to repair. There are literally hundreds of parameters that the PCM is using to monitor and adjust this engine, which one is off kilter?
 

·
Hotrodders.com Moderator
Joined
·
6,391 Posts
Before you go crazy, check the fuse for the cigarette lighter. This is generally the same fuse that supplies power to the DLC connector. Once you can access the system you can start to troubleshoot. Fuel injected systems usually dont work well with "stuff" disconnected.
 

·
Administrator
Joined
·
8,211 Posts
O2 sensors dont have any effect on a cold start run condition.That is where he has his driveability complaint.
I am sure there are others too...:rolleyes:
 

·
Registered
Joined
·
65 Posts
Discussion Starter #16
check engine is now working, but not throwing any codes. I took it down to the shop and they tell me everything is testing well except fuel pump. They say fuel pump pressure is 40-50 and should be 55+.

He says we must replace the fuel pump. It does not make sense to me this would cause the problem. According to him inadequate fuel pressure will throw off the ECM and would be the problem.

I dropped about $300 on a delphi fuel pump.

Any thoughts?
 

·
Registered
Joined
·
65 Posts
Discussion Starter #17
Just some house cleaning.. The check engine system worked. I had it checked at Oreillys and they told me it did not. Sorry for throwing the thread off.

Also, there are no drivability issues other than the one mentioned. After it warms up, it runs like a top!
 

·
Hotrodders.com Moderator
Joined
·
6,391 Posts
Did you check the fuel pressure regulator. Unplug the vacuum line on it and make sure it is not full of fuel. You can also try pinching off the erturn line to see if the pressure goes up. I would not install a pump unless you are sure. It is an expensive guess.
 

·
Registered
Joined
·
65 Posts
Discussion Starter #19
I took the shops word for it. I guess we will see. My tinkering is with older cars and am a real novice when it comes to anything after about oh 1978!

would low fuel pressure account for a bouncing idle at start up? I would think if it was the fuel pump it would happen in and out of gear. MIne only has problems in gear at idle when it is cold
 
1 - 19 of 19 Posts
Top