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94 Rough Under Load?

dichdoc

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dichdoc Enthusiast

dichdoc

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Friends 1994 Chevy ext 1500 350 TBI auto approx. 18,000 on rebiuld. Starts and idles good. After up to operating temp while in gear and apply a load it begins to run rough. Says if he stomps on it from a stop sign it seems to go through the bad area but easing into it it is rough. It had thrown a code for O2 sensor so he replaced it along with the idle sensor on the TBI. Any thoughts things to look for? TB

bill190 Enthusiast

bill190

Posted
Posted

After replacing an O2 sensor, you should disconnect the battery for about 10 minutes, then reconnect, then turn on ignition without starting and don't press any buttons for 1 minute, then start and let idle for about 5 minutes. Drive it above 45 mph as soon as possible.

 

This "relearns" the engine computer to the new sensor.

 

As to the problem, check the fuel system, start with fuel pressure and *volume* tests. More...

http://www.asashop.org/autoinc/june98/techtotech.htm

 

Factory specifications for these tests as well as additional tests for this problem would be in a GM Factory Service Manual set for your year/model vehicle. Order from helminc.com or a GM dealer.

 

You would also need to know how to use a multimeter for many of the tests in the factory manual. How to use a multimeter...

http://www.google.com/search?hl=en&saf...ter&aqi=g10

coconutwil New Member

coconutwil

Posted
Posted
Friends 1994 Chevy ext 1500 350 TBI auto approx. 18,000 on rebiuld. Starts and idles good. After up to operating temp while in gear and apply a load it begins to run rough. Says if he stomps on it from a stop sign it seems to go through the bad area but easing into it it is rough. It had thrown a code for O2 sensor so he replaced it along with the idle sensor on the TBI. Any thoughts things to look for? TB

 

 

Sounds like water in fuel or a bad injector? Try a fuel additive that evaporates water and cleans injectors...Had similar problem with my GMC 2000 1500 4.3...Put additive and now runs great...

kuhl_530 Enthusiast

kuhl_530

Posted
Posted

+1 on the water. Check your ignition coil. I know personally those coils have a habit of going bad after a while, and it can be a hard thing to detect. Symptoms can be hard starting in wet weather, studdering or shuddering, especially under load and especially in wet weather. Also, check cap, rotor, wires, plugs, and the plug gap. All of these could be causing the issue, on the ignition side.

 

On the fuel side, it could be a bad/dirty injector, poor fuel pressure caused by a clogged fuel filter, dying pump, or bad fuel pressure regulator, or water in the fuel. With a fuel dryer being the cheapest of all the solutions, I would personally try that first. I suggest Sea Foam brand fuel injector/carb cleaner. It's a fuel cleaner/dryer/stabilizer, and I've had a lot of luck with it.

dsertich Enthusiast

dsertich

Posted
Posted

In case you havent figured out, i'm the guy with the truck issue from the first thread. I figure i can learn more about it and add any input from you guys. I'm not having much luck with it so far but am still trying everything that is offered.

I get a real rich smell of gas when it gets in that sweet spot when it runs so crappy. When I get on the throttle pretty good it doesnt seem to affect the burpy/rough factor.

What i've done so far:

- replaced o2 sensor (disconnected battery,turned ignition, idled 5 minutes, ran above 45mph) (also was only diagnostics trouble code a few weeks ago)

- replaced throttle position sensor

- added fuel injector cleaner

- replaced Ignition module in 2004

- replaced egr gasket (it had a gap in it) valve seemed to operate ok

 

I planning to replace ignition coil, cap,rotor,plugs and wires next. Any other ideas would be great

2COR517 Enthusiast

2COR517

Posted
Posted

Those TBIs like good AC Delco ignition components. Napa premium wires are sufficient. CR43TS is the plug to use, gapped at .035. Blow out the distributor, and clean the coil post nice and shiny. Check your base timing too. Go with 0* BTDC till you get it running right. You might be able to advance up to 4* after everything is running smooth.

 

Is the TB to intake gasket new?

dsertich Enthusiast

dsertich

Posted
Posted

Well, I have changed out the plugs, wires, cap, rotor, ignition coil, and shined up the coil shaft. (it had some rusty color to it)....and still no results. Any suggestions at this point? It almost seems like a fuel issue to me like it isnt balancing out the fuel ratio, or something maybe plugged, and it also smells rich.

kuhl_530 Enthusiast

kuhl_530

Posted
Posted

I'm pretty stumped at this point... the only thing that comes to my mind now is a fuel pressure regulator, which I'm pretty sure is located somewhere in your throttle body assembly. I'm not suggesting you run out and buy one, cause they're pretty expensive. Just the last thing I can think of off the top of my head.

Mike G Enthusiast

Mike G

Posted
Posted

If you purchase a TBI rebuild kit from say Advance Auto, it comes with really just gaskets and seals. But there is a seal for the fuel pressure regulator in there too. If you are not comfortable replacing the gasket and seals of the TBI, look for a local carb shop, they will probably only charge like $100. But of course, if you go that route, have the trottle plate bushings replaced too, they do not come with the kit you buy at the auto parts store...

--Mike

dsertich Enthusiast

dsertich

Posted
Posted

Any thoughts on an "engine coolant temperature sensor" ? It only acts up when its running at a higher temperature and specific rpm range, but when it's cold, it seems to run fine.

I talked with a mechanic and he made that suggestion. He stated that it may not be communicating with the powertrain sensor. My understanding is that it regulates the fuel/air ratio, which could be why i'm smelling a rich odor?? thoughts???

bill190 Enthusiast

bill190

Posted
Posted
Any thoughts on an "engine coolant temperature sensor" ? It only acts up when its running at a higher temperature and specific rpm range, but when it's cold, it seems to run fine...

 

Is the coolant temperature sensor reading the right ohms (resistance) at various temperatures like it should? (Using a multimeter.)

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