97 Vortec 5.7 pre-ignition and code P0174

[Seeker57]

I have an ongoing problem with my 97 1500, with 68k mi. it started with deteriorating gas mileage, from 18 highway, to 16, I did cap, rotor, plugs,wires, and then after 2 hrs highway driving at 0 deg. F it gave me a service engine light. my nieghbor read the code P0174 "system too lean right bank" I replaced the forward Oxygen sensors and reset the light. it ran good for a week but I could hear light throttle pre-ignition that goes away when you push the pedal harder. It has good power starts easy, runs smooth, I went for another cold weather travel, after 2 hours highway running (cruise @ 75) the light comes on again, gas mileage at 14 mpg truck unloaded. The light will reset itself with in town driving but I still hear the light throttle spark knock, and I want my old 16-18 highway mileage back, I bought it new, it has had only light use and regular maintenance, 68k miles, when it was new I measured an honest 20 mpg once. now my best is 14. Any ideas?

[SpitAndDirt]

P0174 - Fuel Trim too Lean (Bank 2) Depending on the weather where you live, how you use your truck, and what maintainance has been done.....anything is possible, but here are my best guesses. There are several sensors that are monitoring the incoming air. Air Intake Temp and Volume would play a considerable role. But you don't have any codes that are pointing to one of those sensors. So the next likely thing could be a vacuum leak somewhere letting extra air into the intake without being measured by the sensors, hence the lean condition. Why it is only on bank 2 or the passenger side......im not for sure, because a vacuum leak should affect both sides of the engine. You said you only have 68,000 miles on your truck, do you only do short trips? Does the engine get sufficient time to warm up? Do you use the same brand and grade of gas? Have you ever replaced your fuel filter? Checked the PSI of your fuel system? The known problems for our series of motors( I'm assuming you have a 5.0 or 5.7L v8) includes the intake gaskets leaking, the CSFI fuel injector "poppets" getting clogged because of short trips and bad gas, and finally, the fuel pressure regulator(attached to the fuel injector unit under the plastic upper manifold) can become stuck and/or leak fuel. Since not everyone can just pull a fuel injection pressure tester out of their pocket, you can only do so much, but knowing the fuel pressure is really what you need to properly diagnose this problem. I would start with the fuel filter, as it needs to be changed every year or every 12,000 miles. Second, make sure your air filter is free of dust and that all your main intake hoses are properly fastened. No leaks between the Mass Air Flow sensor and the intake manifold. Third, you may also invest in having your computer firmware reflashed at the dealer. You can check your VIN at this website to see if there are any outstanding software updates that would cure some drivability issues. So many people do not understand that some problems can not be solved only by throwing parts. http://calid.gm.com/vci/VINEntryPre.do I would also recommend that you look into the cost of having your FUEL INJECTORS pressure cleaned. The dealer has special equipment that will allow them to isolate just the injectors, and run higher than normal fuel pressure to blast away deposits. If the injectors are too bad to be cleaned, there is an available substitute made by Delphi Products. Funny, Delphi is owned by GM but the original fuel injectors were made by Delco. The down side is that the injectors are expensive at about $450 for the whole unit, but well worth it. The part # is FJ10566, it comes with 8 new injectors and fuel pressure regulator. http://go.delphi.com Just look up your truck and you will find this part listed as a MFI Fuel System V8. I hope this gives you some ideas on what may be causing your problem. Just for reference however, I own a 96 Z71 5.7L, live in Missouri, and use 87 octane from Quicktrip, Exxon, Chevron, and BP(Amoco). I keep my truck in excellent repair, and everything is stock on it. 161,400 miles on the original fuel pump. New pre-cat o2 sensors installed 10K ago. I use all synthetic fluids everywhere except the transmission and Power steering. I run LT265/75/16 tires that are in need of replacement. On the last long trip I took, which was about 650miles, I averaged between 22-24 miles per gallon driving @ about 70-75mph. I dont think you can get much better than that. -Chris

[Seeker57]

thanks for the input Chris, I have the 5.7 and I think that you may be looking in the right place with the short trips, until recently I had commuted 4 miles each way, with a tank of Citgo 87 lasting 2-3 weeks.The engine runs on Mobil 1 5w30 and the fuel filter is replaced each year, when I took off the distributor cap the contactor on the rotor had a hole in it where the coil contact rides, the ignition tune up was done well ahead of any codes. Living in CT I take 4-8 trips a year to VT, NH, & ME, about 200 mi. the last four were cold weather runs about 0-5 deg. F, and the SES light came on each time after about 2 hrs. driving, the pre-ignition that I hear just on light accelleration makes me believe the lean condition does exist. Now do I go for the MFI and install it myself, or have the flush done, that must be farmed out to the dealer. Reading the TSB I see the replacement no longer has a poppet valve so it should never re-occur, with the flush and my driving style is it only a matter of time before I am back at it again?
GM was the last of the big three to own it's own suppliers. I was installing equipment at the suppliers in the '90's while GM was spinning them off into "Delphi" Harrison Radiator became "Delphi Harrison Thermal Systems" AC Rochester became "Delphi Energy and Engine Management" Packard Electric became "Delphi Packard" Delphi is a fortune 500 company itself now and is not owned by GM, who is now just its biggest customer.

[SpitAndDirt]

I do not believe that it is all that bad to install the new injectors yourself, it just requires a bit of patience on your part. That is if you just want to skip further diagnosis and just start throwing money at a known problem/issue with the fuel injectors. I'm not one for just wasting money, are you? I would highly recommend the flush be done first, you may get a good deal and not end up paying as much as you think. Just make sure the dealer actually pressure flushes the injectors and doesn't just run a upper intake manifold cleaner through your brake booster hose. If you do want to tackle your injectors, your going to be dealing with a lot of plastic pieces, especially the upper intake manifold. I don't think that you will have to remove your distributor, but if you do, it is IMPERITIVE that the rotor position and the distributor housing are put back in EXACTLY AS YOU REMOVED THEM. If you do not, then you have to have the dealer use it's GM Tech 2 scanner to adjust Cam Offset or Cam Retard. It's the relationship of the Distributor/Cam postion and the crankshaft. The computer needs a reference point on which to base timing calculations, if the distributor is reinstalled with the distributor shaft one tooth off or the body of the distributor 6 or 7 degrees off, then you will have a service engine light set. Cam Offset is only +/-2 degrees, I believe. But you can forget all that if you don't need to remove the distributor. The cap and rotor burnt out is not uncommon at all, I've seen trucks that nearly burnt through the plastic before the connection failed. I truly believe that a lot of your problems stem from those short trips, you're not allowing the engine enough time to properly warm up. Warming up also means that it will allow moisture that builds in the crankcase to boil off, resulting in cleaner oil, and your fuel injectors will be hot enough to let some of those deposits get softened and blown out. Your cold climate does not help matters much either, so your just going to have to work around it. -Chris