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Dan, Technician
Category: Chevy
Satisfied Customers: 24164
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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Chevrolet Tahoe 4x4: I have a 1997 Tahoe 4x4 5.7 litre Vortec

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I have a 1997 Tahoe 4x4 5.7 litre Vortec and the engine light keeps coming on and I change the plugs, wires and rotor and it works fine and the light shuts off. About 4-5 months later it idles rough and the plugs are bad and I do the same thing over and it runs fine.

I have 185,000 miles on the truck and it runs fine other than that. I haven't done anything major to the engine at all since I bought it new.
Welcome to JustAnswer, my name is XXXXX XXXXX I'm here to help get your problem resolved. Does it ever start hard or run rough? Does it get good gas mileage? What diagnostic code are you getting when light does come on? Thanks.
Customer: replied 4 years ago.

gets decent mileage and it always starts hard - have never checked the codes ever - don't know where to look, probably need to take it in to get checked. Runs rough when the light comes on only at idle. Other than that its fine. I have been told its the coil and numerous other things like the camshaft and crankshaft sensors. I was jsut going to start replacing them all but figured I would ask.

This most likely means you have a bad fuel pump causing low pressure which makes plugs run lean wearing them out too soon or a bad coolant temp sensor causing it to run rich most other things would cause the check engine light to come on. Fuel pressure should be at least 60 psi while cranking if low replace pump, if good replace the coolant temp sensor. THe coolant temp sensor is a cheap part and easy to replace so you could do that anyway first. Let me know if you have any questions, thanks.
Customer: replied 4 years ago.

brand new fuel pump

Customer: replied 4 years ago.

where is the coolant temp sensor located?

Sometimes aftermarket pumps can have problems so I would still moniter fuel pressure if good then replace the coolan temp sensor which is a common problem. Let me know if you have questions or how it turns out. Thanks.


Here is a picture of sensor.

Customer: replied 4 years ago.

ANd my coolant temperature guage has been showing for about a year that the coolant never gets above 125-140 degrees - which I knew was wrong.


I will go get a new sensor tomorrow.


Are they hard to change? Any special tools?

The coolant temp sensor for guage and computer are two seperate sensors, they are easy to change. IF temp sensor still never goes above 140 replace the thermostat also. The sender is for guage and sensor is for computer. Let me know how it goes or if you have questions, thanks.

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Customer: replied 4 years ago.

OK, change thermostat, engine coolant sensor and sensor for the guage, new plugs and high performance wires. Everything was great, it ran with more power, everything was perfect until I drove it 1 hour in about 100 degree temperatures, and on my way home the engine light lit up - it still runs great, but that damn light is on again. What would be the next thing to do? What is the next common issue for vortec's like this one?

Check codes and let me know what they are. You can have them checked for free at your local parts store. Thanks.
Customer: replied 4 years ago.

P0304 bad cylinder #4 - its running beautuful right now, no miss, plenty of power the check engine light is off. I was going to look at changing the coil, new plugs and wires and maybe the injector is bad or maybe the oxygen sensor or it could be a burnt valve. I am looking for your experise here.


ALso have a P1870 which I believe is due to some bad parts in the transmission and I sometimes have hard shifts when its hot.

I agree that I would start with plugs wires. If that doesnt help you could try some seafoam incase its a dirty valve, suck it into intake using vacuum line then let it sit over nighit and run in morning at low gear high rpm to burn out carbon deposits. If that doesnt help make sure there are no vacuum leaks on intake manifold, if not swap injecto with another cylinder to see if misfire moves if so replace injector. The 1870 code usually means bad transmission or valve body, probably better off just replacing transmission. Let me know if you have questions, thanks.
Customer: replied 4 years ago.
The best vaccuum line to use the one coming off the brakes? That goes into the intake?
You can use any vacuum line, I would use pcv hose. Let me know how it works, thanks.