Late model GM fault code experts

[JoePorting]

My general advise would be to replace all the sensors. Most are cheap on rockauto.com. Also replace the coils and sparkplug wires.

[Truckedup]

My general advise would be to replace all the sensors. Most are cheap on rockauto.com. Also replace the coils and sparkplug wires.

Good advice but it runs very well now and I'm tired of working on it I removed the dual exhaust, it was a small turbo type dual out let muffler and twice tail pipes..The stock exhaust on a 4.8 truck is 2.75 inch pipe all the way back and a huge muffler...Not only is it quieter, I get the impression it has a better pull through the gears at part throttle..

[Truckedup]

Here's a follow up on the truck 2003 Silverado 4.8 5 speed manual.....First problem fixed then came another fault code, P0300 random misfire....it makes the check engine light flash, but won't set a permanent code if I back off the throttle or accelerate, then the light goes off....It only occurs in second or third gear or 4th gear on level ground with a steady pedal , no load on the engine, between 2400-2600 rpm. I replaced the plug wires and spark plugs...Now it does it only in 2 nd , 3 rd gear.....Then a friendly shop told me this occurs when rust gets into the fuel system and plugs a few injectors just enough to upset light load fuel delivery at usually a specific rpm range...He said the shop has seen dozens of these caused by rusty fuel lines....Well...When I bought the truck the previous owner said he replaced the fuel lines and tank sender because they were rusty and leaking...Yup, the truck does have new looking plastic lines...A dim light goes off in my head...I just pulled the fuel rails and and removed the injectors...I tapped them on a clean sheet of paper and debris came out of two of them...The fuel rails are plastic .......I'm getting 8 new Delpi injectors and a fuel filter...

[midnightbluS10]

A can of throttle body/carb cleaner is a lot cheaper. Pull em, clean em out, and put em back into service. I'm betting it'll fix it. It fixed 100% of the trucks I worked on at the dealership when I was there. It was quite a common issue. Each time, I'd have to run the fuel system cleaner first and it never fixed the issue. Only pulling the injectors and physically cleaning them out did.

[Truckedup]

A can of throttle body/carb cleaner is a lot cheaper. Pull em, clean em out, and put em back into service. I'm betting it'll fix it. It fixed 100% of the trucks I worked on at the dealership when I was there. It was quite a common issue. Each time, I'd have to run the fuel system cleaner first and it never fixed the issue. Only pulling the injectors and physically cleaning them out did.

I though about cleaning them.....But they may be 13 years old.....8 brand new Delphi injectors is $180 shipped to my door.....

[roc]

A can of throttle body/carb cleaner is a lot cheaper. Pull em, clean em out, and put em back into service. I'm betting it'll fix it. It fixed 100% of the trucks I worked on at the dealership when I was there. It was quite a common issue. Each time, I'd have to run the fuel system cleaner first and it never fixed the issue. Only pulling the injectors and physically cleaning them out did.

I though about cleaning them.....But they may be 13 years old.....8 brand new Delphi injectors is $180 shipped to my door.....

Hummm, maybe the Triumph is getting injected in the future??

[Truckedup]

Hummm, maybe the Triumph is getting injected in the future??

I have given it some thought...But I have doubts than injection would give more full throttle power than carbs on on old junk????

[Truckedup]

I voided the new injectors and tried a set of known good used ones... No difference.Well it does seem to pull a touch better over 4500 rpm ...Fuel pressure is ok.....If the engine is held at a steady 2500 rpm in neutral the check engine light will start flashing after about 20 seconds for as long as it's held at that RPM....Won't do it at less than 2400 or more than 2600 rpm..Let it idle and the light goes off after 30 seconds.It does the same on the road in lower gears..The computer stores a pending code only P300 "multiple cylinder misfires" The exhaust sounds smooths, the engine feels smooth... Maybe I should just ignore it because the CEL does not flash in normal driving...

[BLstangin]

Get someone with a good scan tool and do a crankshaft variation relearn on it. I've seen before where the reluctor wheel get garbage caked on it and it changes the gap between the teeth ever so slightly and at certain rpm it will cause a false misfire reading. If you can't feel an actual miss in the engine that is more than likely the problem. Make sure you clear all the codes first and set the parking brake at least enough for the light to come on or it will not do it.

[582r10]

Usually the ses/cel flashes to let you know your problem can damage the catalytic converters if you keep operating it. Just a fyi

[midnightbluS10]

Usually the ses/cel flashes to let you know your problem can damage the catalytic converters if you keep operating it. Just a fyi

That is correct. Have you checked compression and leak down on that cylinder?

[Truckedup]

Usually the ses/cel flashes to let you know your problem can damage the catalytic converters if you keep operating it. Just a fyi

That is correct. Have you checked compression and leak down on that cylinder?

Yes, that was discussed elsewhere in this thread....It's multiple misfires according to the scanner, no particular cylinder noted..The compression is within specs...The engine idles very smoothy and quietly at 600 rpm and has good power for a 4.8, fuel mileage is normal.....In day to day driving the CEL never flashes....The engine has to be held at a steady 2500 rpm with little or no load to make the CEL flash, and like I said, it doesn't make the CEL stay on steady or set a stored code...

Kinda funny, the injectors I swapped in from a good running engine didn't solve the "problem" but created another problem..On a hot restart after waiting about 45 minutes, the engine cranks a long time before starting..it's obviously a flooded condition, leaking injectors.I did clean the fuel lines, injector rails and use a new Wix fuel filter.Before this problem cam up I replaces all the rusty metal fuel and return lines with high pressure plastic..I'm putting in the original injectors and just drive it... Thanks for all the replies

[Truckedup]

The fuel pressure at idle with the engine warmed up is a steady 48 psi...Hold a 3000 rpm and it's 46 psi....When the engine is reved hard the pressure is 45 and jumps up to 52 momentarily when the accelerator is released....Pull of the hose to the regulator and the pressure is a steady 58 psi at all speeds...

[S10LS2]

Well guess you found your problem. That was quick and easy huh? Best check is to test the pressure under LOAD. That will tell the tale. Fuel pressure is the very first thing to check on any GM truck or any fuel injected engine. Now go put another new filter in it, and most likely a pump. Throw in a regulator for the hell of it, they are cheap. Oh and no chinese pumps here. Find a delco original online.

[Truckedup]

Well guess you found your problem. That was quick and easy huh? Best check is to test the pressure under LOAD. That will tell the tale. Fuel pressure is the very first thing to check on any GM truck or any fuel injected engine. Now go put another new filter in it, and most likely a pump. Throw in a regulator for the hell of it, they are cheap. Oh and no chinese pumps here. Find a delco original online.

Yup, the fuel pressure is suppose to be 57-62 ? I pulled the fuel rail up with injectors attached....Turn on the ignition so the pump runs for a few seconds...All Injectors get wet and some drip fuel...More junk...I'll test the regulator by pulling off the return line and turning on the ignition to see if fuel comes from the return...I'll test the original injectors and if ok ,put them back in...