Truck running horrible....why?

[HardcoreZ28]

I have a 97 1500 with the 5.7 Vortec in it. It's a GM Crate replacement engine with only 25,000 on it. It ran fine for a year and a half and now all of a sudden it's lost all of it's power on the low end and doesn't want to rev much up high either.

I had a code before for a misfire as well as cat inefficiency. I thought my injectors (poppet style) were bad so I replaced them last week with the upgraded Delphi unit. Car threw another misfire code and it turned out I had a wire loose on the cap. I cleaned up the terminal and reinstalled it and no more misfires.

Cat's haven't reached ready stage again yet, but shouldn't be my problem. They have only been on a year. I have to replace one of my after cat O2 sensors still because the parts store only had 1 when I replaced them a year ago.

For no real reason the truck has just lost a lot of power. I've replaced the injectors like stated earlier. I also replaced the fuel filter and checked the fuel pressure (55-60psi while driving). I haven't checked fuel volume yet.

Air Filter is clean and all tubing hooked up correctly. Ignition system should be ok....cap, plugs, wires, rotor all new withing last year and a half. I also just replaced the plug in the cylinder that was misfiring...it didn't looked fouled or gas soaked.

So I'm kind of stuck here for ideas? All I can think of are fuel volume, MAF Sensor, or something else in the ignition system like the module or pickup coil? Any help would be greatly appreciated.

[Mikado14]

You should have the truck scanned and review the data.

[HardcoreZ28]

I'm trying to get my hands on an OBDII scanner. I really despise have to pay other people to fix my cars but with all of the new technology out today it's hard to afford some of the diagnostic tools and sometimes you can't even beg for them anymore.

I was just trying to see if anyone else had had a similar problem that was most likely ignition related or a blown MAF.

[broughy84]

this misfire.....did the plug smell of antifreeze? How did it look? was it gummed up with anything?

[HardcoreZ28]

The plug looked fine. I thought the misfire was from a stuck poppet valve on the injector in that cylinder so I replaced the injectors (they had 125k on them anyway) but it turned out a wire pulled off the cap part way and there wasn't a good spark getting to the plug.

[broughy84]

have you ran a compression check?

[Mikado14]

Just for a little fun, try pulling out the O2 sensor before the cat and take it for a drive. More than likely you will get a code but see if it runs any better.

[HardcoreZ28]

No compression test as of yet. GM crate motor is only a year and a half old. Only reason I could be losing compression is if the misfire cylinder killed the ring seal on that cylinder, but I doubt it.

I will to the O2 trick and also checking my fuel volume as soon as the truck runs again!! That's right....it really took a dump on the way home from work last night. Fan clutch broke and sent the fan right through the radiator. Hopefully have it running again tomorrow. This just keeps getting better and better.

[skipr]

You can have a commpression leak in the valves or the rings, A wet commpression test would be more accurate or better yet a leak down test. As long as we are on the subject if all cylinders were 175 psi and one of the eight was only 155 would you consider that a problem? this question is directed to anyone.

[HardcoreZ28]

My problem was the fuel pump as I suspected. If anyone saw my other post about fuel volume you'll see what happened.

As for your compression test, you are only at 10% variance. While it's not great, it's still within the acceptable range. Let me guess...is it on an end cylinder?

[skipr]

#5 , I was told by Chevy dealer that this is why I have a misfire. I'm not buying that reason because first of all it's intermitent, and second the book says I am within the maximum allowed difference. If i idle too long the SES comes on , then goes out after driving a few minites.

[HardcoreZ28]

Sounds like a leaky injector/poppet valve to me. GM had a huge TSB on those horrid valves to clean and then later replace them. They all last less than 50k before they start sticking. I have an extra Delphi upgraded unit that I am getting ready to sell. It has 8 seperate injectors in place of the poppet valves and costs the same, if not less than a new set of GM injectors. If you are interested in it shoot me an [email protected]

[skipr]

Yea I agree about the poppets. I metioned this all THREE times I have brought it in, they immedatly rule out that being cause and charge me $85 hr. , have me replace things that did not need replaceing still haven't found it (this has been going on for year and a half) this last time I cancelled my check I wrote for $330 for 4 hrs of troubleshoot, right after I got my truck back. They suggested a valve job, I suggested they give me a blow job. Mr goodwrench my ass!

[HardcoreZ28]

HAHAHAHAHAHAHHAHAH