TBI Guru's please help:Long wind.....

[conoverbandit]

Hello,
I need some help diagnosing a problem on my truck. I have a 87 chevy R-30 crew cab dually with 454.It's been sitting for quite some time.I bought it 4 years ago from a friend and been pouring money into it ever since as time, "extra money" permit. Ok, enough now the problem. It consistently dumps fuel into the tbi, It will not go into "closed loop" (I have access to a diagnostic system from where I work.) Engine acts as if it has a "choke" on it sometimes, meaning idle is up and fuel is- well. (it can have as much as 2-3 tablespoons on top of the butterflies at any one time it's running) It will "surge" too just sitting in park, idle goes up and down. If you put into gear the surging will stop, but then it starts missing,and chugging smoke out the exhaust,and if you try to move it sometimes dies. To date I have done the following to try at repairing it with no luck: replaced all gaskets on the tbi, new fuel pressure regulator,new 02 sensor, new coolant temp senser, new timing chain and complete new dist.(thinking it was in the timming), changed MAP,IAC,TPS, new coil also. All these have helped, but no fixed the problem. I did not buy all new sensors because some of these are expensive. But since doing all this I have hooked up truck to Diagnostic computer and doe test's on all systems and it tells me that all sensors are within normal operating peramiters. I also exchanged the injectors themselves with some from a running truck.I did buy a new ECM and put it into truck but all it would do was spin over it would not run, so I put my old one back into it and it fired right up but still has same problem. I'm sorry for being so long, but I just wanted to give as much info as possible so you could get the idea. Any help would be GREATLY appreciated. Thank You for your time,

Wayne

[C&C Chevy]

It's curious that your not getting a code 45. Have you checked your emission hoses, egr, charcoal canister? Since you can get a diagnostic read out. I would take that and head over to http://www.thirdgen.org/techboard/tbi/ . Very knowledgable TBI forum over there.

[conoverbandit]

Hadn't thought of that.I went and registered at thirdgen. Thanks for the reply

[Russell]

Just don't mention that you are working on a truck -- They can be purist to Camaros there, lol

[SSC's76]

TGO will be very helpfull with this problem just do a few searches before you post. It get a little annoying seeing the same post over and over again and alot of arseholes have poped up and like to rip others apart for what they consider repeditive questions.

I find it hard to beleive the scanner showed no problems especially since the truck wont go into closed loop. Closed loop cannot be enabled if the coolant temp sensor is not reading the proper temp. I would check again with a scan tool to see what temprature the sensor is reading. Alot of people replace the tstat with a cooler one and it can prevent closed loop. I would also check the EGR like mentioned above. If its stuck open it will also cause the engine symptoms you describe.

[Russell]

I tend to agree with SSC too, my first guess would be CTS, but that should set and error code, and a scanner would show the problem right away...

[conoverbandit]

Thank You for all the information.I did not realize that a EGR valve would cause this,I will check it and see if I can borrow the scan tool again.I did replace the T-stat with I thought a cooler one, after doing research and figuring out these things have to run this hot,I bought a 195 and installed it to see if this would fix it, only to look at the new one I pulled out to see "195" on the bottom of it...........Oh well I got a replacement for it if it ever goes bad LOL. Thanks,

Wayne

[7387chevys]

Have you ever thought about going to a tri-power setup.........or a quad
Shane

[rfmaster]

Conoverbandit

You have some issues with TBI – Do not give up! Let us take this problem step by step.

First step:
I suggest getting a cheap laptop with ALDL cable with a free TBI diagnostic tool. You can get cable from:
http://www.aldlcable.com/

Software (free):
http://winaldl.joby.se/

You can control ALL ECM functions and perform basic data logging with this setup as well monitor error codes.

Second step:
Quote (it can have as much as 2-3 tablespoons on top of the butterflies at any one time it's running) To date I have done the following to try at repairing it with no luck: replaced all gaskets on the TBI, new fuel pressure regulator, new 02 sensor, new coolant temp sensor, new timing chain and complete new dist.(thinking it was in the timing), changed MAP,IAC,TPS, new coil also.

You mentioned that you have replaced fuel pressure regulator. In TBI systems fuel pressure is relatively low – 12 to 15 PSI for system to be happy. If by a chance some one replaced fuel pump with TPI version fuel flooding will result. You can perform a “dead head’ fuel pressure test to verify that fuel pressure is around 12 to 15 PSI.

Third step:
TBI injectors are controlled using PWM waveform. An ECM (electronic control module) has four wires that provide signals to rapidly open and close injectors. PWM stands for Pulse Width Modulation. In another words injector is rapidly opened and closed over a very short period of time in order to produce a finely atomized fuel spray. Fuel poodle on top of throttle plates may indicate that one of injectors is stuck open. Three ways to check for that. First, take timing light and connect it normally i.e. cylinder one spark plug wire. In a dark garage point it at the TBI injectors and observe fuel spray. There should be a mist like flow from both of them. Second, a bit more complicated way, which requires someone with serious electronic skills. You need to measure injector PWM waveforms with oscilloscope. If you know some one with O-scope - great. A stuck control line may cause injector to be stuck open! Third, and it is highly unlikely – a cracked TBI housing causing fuel leakage into TBI well – it can happen if TBI is over torque...

Let me know what you find

Also let me know service number and broadcast code of your ECM. They should be on the label attached to the ECM housing.

One more thing to check. It's possible that fuel pressure regulator inside TBI is leaking due to old gaskets or was adjusted too rich.

//
RFmaster