GoChevy

This is a long post and I apologize for that but I’m hoping to give enough information that someone can help me out.

Here is a little history on my truck: it is a 1997 K-2500 with the 5.7 Vortec and 134,000 miles and has been very well maintained. The thermostat stuck while my wife was driving and she didn’t notice the temperature gauge maxed out. The plastic top of the radiator cracked and the water pump blew out at the weep hole. I replaced the water pump, radiator and thermostat and all seemed well. We continued to drive it for a few months and then I used it to pull a fairly heavy trailer and shortly after the truck started to overheat again and I could see indications of water in the oil. The truck was still running great at this point. The only indications of a problem were the temperature going higher than normal and a small amount of milky white residue on the oil filler cap.

I pulled the heads assuming it was a cracked head or blown head gasket because this thing got seriously hot. I noticed while disassembling the engine that several exhaust bolts had broken off. The heads were taken to a very reputable local machine shop, disassembled, cleaned, checked for cracks and rebuilt. Unfortunately at this point I developed a heart problem that kept me in and out of the hospital for months at a time. Because of this the truck sat disassembled for over a year. All the parts were under a covered area so there was no direct rain or sun but were exposed to the weather which was obvious when reassembling because of the light layer of corrosion on just about everything. I didn’t anticipate the extended time the thing would sit in pieces but knew it would be at least a week before I got the heads back from the machine shop so I had sprayed the cylinders down with oil and taped the fuel supply & return lines to prevent contamination so everything under the hood still looked good.

The truck was reassembled with the rebuilt heads, new distributor cap, rotor, wires and plugs. It started right up but has an almost consistent miss at idle, during acceleration and while cruising. It is a very rough idle and lacks power. The check engine light comes on within a few blocks of driving, first setting a P0303 cylinder #3 misfire code which then clears on its own and is replaced by a P0300 random misfire code. My first though was I screwed up the valve lash so I pulled the valve covers, backed everything off and started over ending up with the same results. I performed a compression check which showed all cylinders really close to 180 PSI so I think/hope I have ruled out an engine problem.

I then removed the new aftermarket (Accel) wires, cap, rotor and plugs (Autolite) and replaced with new OEM AC/Delco ignition components again ending with the same results. I swapped out the plug and wire from #3 with another cylinder to make certain it wasn’t just a coincidence of two bad parts in a row and also tried my original cap and rotor. No go.

I thought maybe the fuel went bad from sitting so I ran it out and replaced and added a couple of bottles of fuel injector cleaner also replaced the fuel filter. Again, the same results. I did a fuel pressure test and I got about 62PSI when not running with key on and about 57PSI while running with a very slight dip to maybe 54PSI for a split second under hard acceleration but this immediately rebounds to about 57PSI. The only thing that seemed unusual is when the vehicle is turned off the fuel pressure drops within a few seconds to about 10PSI and the exhaust smells rich. It does NOT however have any starting issues, even after sitting for weeks it will start as soon as the key is touched.

I pulled the plugs again today to double check compression and noticed #3 was fouled up. This is after about 300 miles of driving. I replaced the plug with a new one and the truck ran great for about 4 blocks. Still a slight miss but it was a huge improvement, then the check engine light came back on (P0303) and it started running rough again. So I’m lost at this point and don’t have the energy (more heart surgery in my future) or money to keep messing with it but I really need it as transportation. I’m thinking a CSPI to MPI conversion kit but don’t want to throw over $400.00 at it without being certain and am unsure of how to test beyond the basic fuel pressure test. Any feedback on what to do next would be greatly appreciated.

LARIDERS

I would start by having it hooked up to a good scaner and see what one or ones are giving you trouble. you can watch the misfires on the computer and see what's going on and then go from there.

GoChevy

What kind of good scanner are you referring to? I have an Acton 9185 that provides basic info. What data would I be looking for? I have seen some posts around here mention a misfire count but my code reader doesn't provide that much of an insight. Do you know how to diagnose a fuel injector issue on this engine? I really would like to know how to determine if they are the cause.

GoChevy

For anyone that may read this thread and wonder replacement of the fuel injection spider assembly cleared up the problem. The truck runs great again.

maxxman04

gochevy, i wished i'd a caught this thread sooner. had same exact problem with my 98 tahoe, same exact fix. tho i do wonder, did you replace the spider with the stock, poppet style injectors, or did you upgrade to the mfi conversion?

GoChevy

I went with a stock setup that I found super cheap because the truck has basically been cast off as a rarely driven second vehicle. It was important to have it running again but due to its age, thirst for gas and high mileage will never see use as a daily driver again and therefore didn't warrant the upgrade. I seriously hate taking a shot in the dark like this and changing parts based on a hunch instead of doing a proper diagnoses but fortunately I got lucky.