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Please Help Diagnose My TBI

nvrenuf

nvrenuf

Holy crap, it's running!
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First the truck - 91 "V" series crew cab with a bone stock 350 (170k miles)

The problem - on initial crank up (1st time or 10th time) the motor has a horrible miss. I can rev it up to about 2k and it will clear out within 10~15 seconds and perfectly smooth (the change to good is very sudden). The problem is worst with temp extremes in either direction and best (meaning less time to clear up) around 70* (almost nonexistant if it's rainy). While acting up I can see black smoke from the exhaust but this goes away also. I'm also experiencing very poor fuel economy.

I have GM service manuals but the info given assumes I have a scan tool. I have a laptop but the available Win ALDL software I have found does not cover my ECM (it seems to be an odd part number do to the 4L80E application).

I'm lost and don't want to just start throwing parts at it. Any help is greatly appreciated! :dunno: :1zhelp:
 
just a guess ICM due to temp related misfire. I just bought a code reader from CSK it was only about $30 but worth it for the time saved on trouble shooting.
 
I've checked for codes using a "key" and none are set.

ICM = ignition control module inside the distrib?
 
You have an autozone nearby? They are supposed to let you scan the vehicle with their free tools.

Check out tunerpro RT for tuning software. I know it will work with the 160 baud ECM's, perhaps you will get lucky and your ECM is already covered...winALDL is getting pretty long in the tooth.

Also MIGHT want to check out the DIY-PROM section of thirdgen, both searching and finally asking. It may be out there, just not commonly available. diy-efi.org, GMECM archives is another place to look for info.
 
John,
I have got a scanner and an extra set of sensors for troubleshooting if you want to come over and use them. I am still trying to get the TBI working on my 454 engine right now. I will be replacing both in tank pumps this weekend with higher pressure pumps to hopefully get more fuel to the engine.

Russ
 
I'm not sure if the 91 had this or not, but you may want to check out the intake air temp sensor.
 
I'll prob catch hell for telling this but I fought with my TBI not running right for 2 months. No codes were registering. I changed, plug wires, coil, fuel pump, fuel filter, map sensor, temp sensor, AIC, TPS, cap, rotor button. .......turned out to be the plugs, sorry ass bosch. A new set of AC delco and she fires right up and purrs like a kitten.
 
Black smoke in those circumstances would signify too much fuel into the mixture. That would also be (or at least part of) your economy problem. The TBI cant really handle a lot of gas until it warms up a bit.

Has a very similar problem a few years back, ended up being a fuel injector oring.

I would check the fuel pressure and check the spray pattern of the injectors with a timing light. Before you do this, double check your timing and firing order. Let me know what you find.
 
put a pressure gauge on the inlet fuel line and block off the return key upo the truck then back off. observe the fuel pressure and check it in 10 min again if its dropped more than 3 psi your injectors are leaking down causing your problem. it would be dripping fuel in when the truck is off causing a very heavy rich condition on start up.
 
x2 that
gmtech954 said:
put a pressure gauge on the inlet fuel line and block off the return key upo the truck then back off. observe the fuel pressure and check it in 10 min again if its dropped more than 3 psi your injectors are leaking down causing your problem. it would be dripping fuel in when the truck is off causing a very heavy rich condition on start up.
Click to expand...
 
Man, THANKS for all suggestions!!!

Russ / Scott, this weekend is out but I'll probably be hitting up one of you guys in the near future to abuse a scanner. :D

GMTech954, how do I block off the return line? Mine has hard line almost the way. Do I disconnect it and find a plug for the TBI fitting?
 
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