Central Port Injection (4.3 L Vortec) lesson learned

I am posting this here for mechanical novices or people like myself with just enough knowledge to be dangerous. Here is a hard learned lesson in not checking/fixing the obvious first. For the most part, no trouble
codes were available to diagnose the problem.
Around June 2005, I noticed my '93 Jimmy was running a little rougher. I figured, okay, time for new plugs, or wires, or something. I read a bit on the internet and heard about the Central Port Injector "spider" problems, but I really didn't want to believe it was anything so expensive.
So, I changed my plugs, and wires, and distributor cap and rotor. They were a little old. After that it seemed that it ran smoother. It could have been an example of the placebo effect. Things continued on this way for months, it was a little rough at idle, but it seemed to work fine once you got going. Somedays, there would be no trouble at all.
Around November, I got my first and only trouble code, EGR valve. I took it to a local garage, and was informed that the EGR valve was all carboned up and seized. First expensive repair, about $500 (part+labor). Things seemed to run better after that, and this time, it was probably for real.
Finally about 3 weeks ago, it got noticably rougher at idle. Things were fine when cold, but when warmed up, it would have a lot of trouble. Hot starting was quite difficult. It threatened to stall when stopping. This was all probably due to fuel leaking into the injector manifold bowl and getting evaporated into the engine. A "carburator" in a fuel injected engine. I of course balked at the possibility that it was the CPI unit. I also noticed about 2 months ago that the oil pressure would go down a little more when stopped. Not below "safe" levels, but still... This was probably from uncombusted gasoline getting into the crankcase via blowby, and thinning the oil. So, I changed the oil again (about a month ahead of my normal 3 months schedule), and changed all the plugs, figuring that perhaps the "champion" plugs were lower quality. I put "genuine" AC Delco plugs in. Of course, the problem did not go away. I also thought that perhaps an accessory was causing the engine to slow down at idle, so I took the belt off and checked everything. The alternator seemed to have some resistance, so I changed it. Perhaps unnecessary, perhaps just good preventative maintenance.
The rough idles/near stalling got worse, and I started reading up again. I completely forgot about the CPI spider issues until this last weekend. By this time, of course, no auto parts place could get parts in before Monday, when I would have to go back to work all week.
On Monday, it was basically undrivable once warmed up. So I finally had to get it fixed, and by now I was finally convinced the CPI spider was bad. Weather and work conditions would not permit me to do it myself, so I shopped around for a garage to do it. The cheapest place I found that didn't answer, "WTF is a CPI?" was actually a local GM Dealership. The total damage came out to about $1000 (Canadian) before tax. Pretty expensive, but better than the garage that wanted $1300 (including $45 for the air plenum gasket). Things seem perfectly fine now. The old unit looked in real rough shape, the manifold was washed completely "clean" on the right side where the regulator is, and a bit on the left side too. Of course all the residue and varnish that was in that side had probably gone into the cylinders.
Of course, there could be lingering problems. Thinner oil resulting from gasoline getting in there probably did some good wear to the moving parts. The right hand side was running rich, and the left lean, and I doubt that this makes for a well balanced running engine. I changed the oil immediately after the repair, and will probably change it in a month again before going back to normal intervals. Perhaps the oxygen sensor and the catalytic convertor took some extra wear they shouldn't have and will cause problems down the road. The EGR valve would probably have been fine without the extra gas going through.
So the lesson here, is check the obvious thing first. And if you have a Vortec with CPI (VIN Code W, between 1992-1995) that takes a turn for the worse, it's probably the CPI unit. If there's no codes, well, it probably isn't a sensor (went down this path for a while too). Also, if your oil level goes up, even slightly, you probably have a CPI problem. You'll just pay out more if you try to look for other problems first. If I had replaced the CPI pod in the summer, I could have done it myself in excellent weather, and probably saved about $400 in labor.
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Did they replace the "nut kit" as well? This kit includes the inlet and return line from the back of the intake to the injector.
wrote:

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Yes.
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wrote:

Cool, that engine should go another 100K miles...
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wrote:

Oops, another reply. You might have saved more than $400 in labor. I bought the parts needed for about $400 US, maybe $350. Took me about 8 hours but I took my time since it was close to or over 90 outside and I was working in the sun.
The EGR is a separate problem. Mine threw a code 32, the pintle was stuck open. Had a dealer replace the valve and Eprom (updated to keep the valve open longer on decel to blow the carbon out) for free under a now-expired service bulletin. The bulletin is likely still valid, but the free repair isn't, it was a limited extension on the warranty to cover only that part for an extra few years/miles.
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First off - you really don't have a hard earned lesson here. You have a 1993 vehicle that has served very well for years and has experienced some wear over time. That's the nature of things. You include a lot of unfounded speculation in your comments below, but nothing to substantiate that speculation. Parts wear out - that's the nature of things. You can replace them before they do, as they do or after they do, but to suggest a hard earned lesson just because parts wore out is being a little difficult on yourself.

That's a perfectly reasonable initial approach.

Unbelievable - $500 for an EGR????? Something is dreadfully wrong here.

Your speculation could be accurate, but it could just as well be the nature of a 1993 engine showing signs of age and wear. All engines drop oil pressure at an idle - it's the nature of oil pumps. Aging engines or weather conditions may show this to somewhat more of a degree. Want to be sure? Spend $20 and get an oil sample analyzed. Gas in the oil is pretty obvious though. You will smell it, the oil will thin. Even at that - gas in the oil, limited to a certain amount, is not necessarily catastrophic to an engine, so premature worry is not necessarily in order.

That's the law. Think that's bad, try plumbing. The Biblical Law governing plumbing is that not only will the hardware store be closed, but you'll be required three more trips to it.

So what? No big deal.

EGR's clog. Read up on what they do in life. You're speculating too much.

True, but again... you went down a perfectly acceptable path absent better information. It's always best to examine and attempt the appropriate lower cost, equally likely approaches first. You didn't hurt yourself by taking the path you did. The parts you replaced needed replacing anyway - including those junk Champion plugs.
--

-Mike-
snipped-for-privacy@alltel.net
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hell the 99 jimmy that we owned, we had problems with the CPI unit also, and before it hit 95k one of the injectors went out.

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