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ECUM acting weird?????


briang0
11-26-2010, 08:40 PM
I have a 94 K1500 with a 350 TBI eng. I have been having a problem with it not idling right when cold it doesn't get above 1000 rpms. So far I have check the timing it's right at 0 which is were the book says it should be. In the last 6 months I have replaced the CTS, Fuel pressure regulator, plugs, wires, rotor, distributor cap, ignator mod, Fuel pump, sender, tank, fuel filter, both fuel lines, MAP, and TPS. I even rebuilt the throttle body. I have cleaned up all the grounds and replaced the ones that were broken. The cold start issue really didn't start until just recently. Most of the stuff I did was for general maintanence. Today I hooked up my computer to the truck and let it start cold and run up to operating temp. I have the file from DataMaster 0d if anyone wants to look at it. What it shows is the truck is running rich. When cold it will start and idle somewhat rough it will run and smooth out as it warms up. I let the computer run for about 25 minutes everything was normal for about 15 minutes after that I started getting a bunch of module communitcation errors. I'm wonder if there is a problem with the ECM possible heat related. The only things I have not replace for the cold idle issue is the IAC and Oxygen Sensor. Now I'm wondering if the problem is with the ECM Any ideas or a possible next step.

Blue Bowtie
11-27-2010, 03:08 PM
It should read rich until the system hits closed loop. Post up the OČ mV and crosscounts in both open- and closed-loop modes. Try to include the injector PW and target vs. actual idle RPMs.

Once in closed loop the BLMs should run right about 128 or so. The short term fuel trim on a cold engine will be a bit positive, and should go a bit negative once closed loop is achieved. The LT trims (BLM) should remain close to zero once the PCM has relearned everything after some drive cycles.

I've experienced this before on a TBI and finally discovered I had a problem with a brand new PCV valve. I had done much the same thing as you have, replacing or servicing the plugs, wires, FPR, injector pod, hoses, TPS, IAC, EGR, MAP, the complete TB, and about everything else involved. Out of desperation I finally cleaned up and installed the old AC-Delco PCV valve that was still on my workbench after a few weeks and everything returned to normal. The aftermarket (F**M) unit I installed apparently wasn't calibrated properly or contained a pintle not designed for the application (there are two balancing springs and a ported pintle to control air flow under various vacuum conditions). The aftermarket PCV did not allow enough air flow at 19" Hg and the IAC couldn't make up the difference. The system relies upon the correct PCV air flow and only trims the idle with the IAC. It might be worth a look to save your the weeks I spent diagnosing my TBI.

briang0
12-31-2010, 11:12 PM
I am still having trouble with the truck. I tried replacing the IAC and it made no difference. Here is what I have noticed. When the truck is cold and I start it up it will run, it is idling at 1000 rpms but it is a little rough. It chugs when I put my foot on the gas. After a few minutes it smooths out. Also there is a definite smell of fuel in the exhaust. After it warms up it idles fine nice and smooth. If I shut the truck off and wait about 10 minutes it will start right up but after idling for a couple of minutes it will stall out. What happens is the rpms will drop a couple of times and then it will die. It starts right back up and will be fine as long as I give it a little gas after it starts. I am going to check the fuel pressure tomorrow but I installed a brand new fuel tank and pump assemble in October so I'm not expecting a pressure problem but stranger things have happened. I'm getting read to send it to the mechanic I'm getting tired of spending money and time on it just want it fixed.

MT-2500
01-01-2011, 08:27 AM
I am still having trouble with the truck. I tried replacing the IAC and it made no difference. Here is what I have noticed. When the truck is cold and I start it up it will run, it is idling at 1000 rpms but it is a little rough. It chugs when I put my foot on the gas. After a few minutes it smooths out. Also there is a definite smell of fuel in the exhaust. After it warms up it idles fine nice and smooth. If I shut the truck off and wait about 10 minutes it will start right up but after idling for a couple of minutes it will stall out. What happens is the rpms will drop a couple of times and then it will die. It starts right back up and will be fine as long as I give it a little gas after it starts. I am going to check the fuel pressure tomorrow but I installed a brand new fuel tank and pump assemble in October so I'm not expecting a pressure problem but stranger things have happened. I'm getting read to send it to the mechanic I'm getting tired of spending money and time on it just want it fixed.

Many things can cause your problem.
And do not rule out fuel pressure even with a new fuel pump.

Got any codes?

Code 45 rich exhaust can be caused by a lot of things.
Here is 10 of them.

Fuel pressure,injector leakage,HEI Ign shelding,canister plurge valve.coolant sensor,map sensor,tps sensor,02 sensor contamination,Egr Valve stuck open and large vacumn leaks.
First thing to check.
If you have a scanner read out coolant tempt sensor and TPS voltage and Map sensor voltage for up to specs.
Post back voltage readings and tempt sensor reading on them.

j cAT
01-01-2011, 10:53 AM
I am still having trouble with the truck. I tried replacing the IAC and it made no difference. Here is what I have noticed. When the truck is cold and I start it up it will run, it is idling at 1000 rpms but it is a little rough. It chugs when I put my foot on the gas. After a few minutes it smooths out. Also there is a definite smell of fuel in the exhaust. After it warms up it idles fine nice and smooth. If I shut the truck off and wait about 10 minutes it will start right up but after idling for a couple of minutes it will stall out. What happens is the rpms will drop a couple of times and then it will die. It starts right back up and will be fine as long as I give it a little gas after it starts. I am going to check the fuel pressure tomorrow but I installed a brand new fuel tank and pump assemble in October so I'm not expecting a pressure problem but stranger things have happened. I'm getting read to send it to the mechanic I'm getting tired of spending money and time on it just want it fixed.

with your engine I do not have the exact details . I believe however your air cleaner should have on the TBI a hot air tube to the exhaust manifold. the air cleaner has a temp door to keep the air entering the engine at a warm temp during cold weather ..is this working correctly?

with this missing/ rusted off, or stuck to allow only cold air to enter the intake you will have the issues you describe..

vacuum leaks must be checked with a vacuum guage ..most times at the engine these hoses get damaged...but this old could be anywhere which is why I suggest the vac guage...PCV operation can be checked with this.

the engine coolant sender must be working correctly to properly control the fuel mixture .

If the computer/ecm had bad ground this could very well have damaged it.

kiwikate76
01-01-2011, 10:56 AM
how do i start a new thread? sorry, i know this is off topic

MT-2500
01-01-2011, 03:16 PM
how do i start a new thread? sorry, i know this is off topic

Open the forum you want to post in and look on left side midway on webpage and hit the new thread button.

MT-2500
01-01-2011, 03:21 PM
Like here on left side page.
New thread button right over threads in forum.
http://www.automotiveforums.com/vbulletin/forumdisplay.php?f=1453

jrecken
01-01-2011, 03:38 PM
I have a 95 k2500 with 350 and I had similar problem. Had to replace the egr and that corrected the problem.

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