[rcman989]

I have been going round and round on this truck with no final fix. I have a 1997 Chevy 1500 5.7 V8, 4L80E. For the past 8 months now it has been running poorly. It will not idle right when in drive, but in park it is better. It will loose power when at speed and when accelerating. It has had cylinder 7 misfire, random misfire, rich, and 02 sensor codes.

I have replaced all spark plugs (AC Delco), spark plug wires (summit), distributor cap & rotor (AC Delco), coil, driver side 02 sensor, fuel filter, fuel pump 1 year ago, and coolant temperature sensor. About 3 months ago I did a Blackbear tune and with that had my EGR valve tuned out (EGR valve and hosing all removed with header install). One day it will be perfectly fine, the next day it will run terrible. After I did the O2 sensors and coolant temperature sensor (did both at same time) it ran better, but still has a slight hesitation / bog. I just took it on an 8 hour trip and it ran fine until the last hour of the trip it bogged and did not want to accelerate.

I have had suggestions of TPS, knock sensor, fuel pump, only use GM wires (I tried AC Delco but they did not affect it so I returned them), fuel pressure regulator, EGR valve (I don't have one), etc. I am getting tired of spending money to no avail, so anyone else expereince and fix this problem before.

 

[SkyHigh98]

poppet injectors?

 

[Hogg]

When it is acting up, what happens when you hold it at WOT for at least a few seconds?

Did you install new O2 sensors on both banks, or just one? You stated both answers.
Were they precat O2 sensors?

Fuel pressure? Gauges are $20. Specis 60-66psi at Key On ENgine Off(KOEO) Key On Engine Running will be slightly less.

Could be a vacuum leak, take some brake cleaner and spray it around all selaing points of the intake. If the engine idle changes, you have an issue. Make sure the a/c and blower are in the off position so the compressor doesnt cycle.

Sometimes its cheaper to have a mechanic do the work, they have the diagnostic equipement.

Could be poppets.

peace
Hog

 

[rcman989]

When you hold it at WOT the first couple seconds it does nothing, then all of a sudden it will down shift and will accelerate fast.

Sorry O2 sensor was only the driver side, passenger side was not done yet. When I check the codes, it is for the driver side and has a high voltage reading, meaning it is rich.

I will probably check the fuel pressure this week. If it is rich wouldn't fuel pressure be fine? Kinda confused as to why, so just for my own reference.

AC system is removed due to caved in condenser, but I can check for a vacuum leak as well.

Hopefully not a poppet injector.

Thanks for the feedback

 

[915WhtRado]

throttle position sensor on the throttle body usually goes out and causes that to happen. some are serviceable but some are part of the whole throttle body.


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[915WhtRado]

part is serviceable seperate, part# 17123852 throttle position sensore $83.57


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[rcman989]

Well not a TPS. Got a new one today and had the same problem. Tried spraying seafoam to find a vacuum leak and nothing. Hopefully with get fuel pressure gauge soon to test that.

 

[Slick_Sierra]

My truck has felt wrong since i got it and gets worse mpg than my last truck, which had the same motor

had to get a new pcm last week, now it's showing knock sensor codes, and throttle body codes. going to get that fixed and see if it changes things. I guess my old pcm didn't read the engine codes, could be knock sensors for you too

 

[915WhtRado]

well that sucks, have you tried getting a good diag from the dealer


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[rcman989]

I didn't wanna pay the $100 fee I know they will charge, but at this point I might as well. I just don't want to pay for a repair I could do. Hopefully I can have them diagnos it and it is a problem I can fix.

 

[915WhtRado]

if its a simple thing, just decline/refuse the repairs and just pay the diag


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[rcman989]

Had a conversation with an owner at a repair shop. He pointed me towards the MAF sensor. I decided to get my code reader out with I can view live data. I noticed when monitoring MAF rates at idle when idling good it would be about 0.9lbs/min (~500-600 rpm), but when it idled like crap, the reading rose from 1.0lbs/min to 1.3lbs/min and sat at 1.3lbs/min, this was also at a lower rpm range ~500-600 rpm. The throttle position remained the same for both. This would make sense for a rich condition that it says it is getting more air, so needs more fuel, but the throttle plate doesn't allow air by. I will clean it tonight and see if that helps the cause.

 

[Hogg]

At idle the IAC will allow more idle air into the intake, regardless of throttle position..

peace
Hog

 

[rcman989]

Replaced Mass Air Flow Sensor and has been running good ever since.

 

[Matthew Gan]

I have been going round and round on this truck with no final fix. I have a 1997 Chevy 1500 5.7 V8, 4L80E. For the past 8 months now it has been running poorly. It will not idle right when in drive, but in park it is better. It will loose power when at speed and when accelerating. It has had cylinder 7 misfire, random misfire, rich, and 02 sensor codes.

I have replaced all spark plugs (AC Delco), spark plug wires (summit), distributor cap & rotor (AC Delco), coil, driver side 02 sensor, fuel filter, fuel pump 1 year ago, and coolant temperature sensor. About 3 months ago I did a Blackbear tune and with that had my EGR valve tuned out (EGR valve and hosing all removed with header install). One day it will be perfectly fine, the next day it will run terrible. After I did the O2 sensors and coolant temperature sensor (did both at same time) it ran better, but still has a slight hesitation / bog. I just took it on an 8 hour trip and it ran fine until the last hour of the trip it bogged and did not want to accelerate.

I have had suggestions of TPS, knock sensor, fuel pump, only use GM wires (I tried AC Delco but they did not affect it so I returned them), fuel pressure
regulator, EGR valve (I don't have one), etc. I am getting tired of spending money to no avail, so anyone else expereince and fix this problem before.

got the same problem buddy I'll be working on it for months and still the same thing hesitation and bogging I'm getting ready to replace my knock sensor is that fixes it I'll let you know but my next step is knock sensors and go to injectors updates the injectors to multi-port injection