Troubleshooting GM TBI

Ah nevermind. The damn thing just developed a heinous rod knock on the way back to work from lunch. Not sure what I'm doing about it yet. Not even sure if it's going to make it home. The truck is worth saving, definitely, but it's going to be a while before I can afford to deal with it.

I guess if I had to get a bad engine, at least it's an SBC. When the time comes I should have plenty of reasonable options.

 

Sry to hear that. Small bonus sbc easiestengine to find a replacement for gl

 

I went through that on our Vette. Talked to several good mechanics, explained symptoms, did what I was told . Ending up replacing the entire fuel system before I got the right part.....the pressure regulator. Was told it would leak gas out of the vacuum line if it was bad, mine didn't, so I assumed it was good, it wasn't , it was sticking.

Dang Drew, I hate to hear that!
Sounds as though the previous owner knew it was about to go and unloaded it on you.
If you can, fill it up with Lucas, even if you have to have to drain some oil or overfill it a bit. The damage is done, the crank would need turning anyway, so the Lucas should keep it from seizing up on you.

You are right, SBC's are everywhere, cheap. Shouldn't be too hard to find one in good shape reasonable.

 

I suspect that's true, but I still think I came out ok on that trade...

I got a truck with a perfect rust-free body and great paint, a nice interior that won't need much to be right, and a bad engine... I can fix engines and I can scrounge up a few odd interior bits. Paint and body work is expensive.

For that I swapped my '73 Ranchero, which is NOT on the verge of throwing a rod, no, but that engine's not totally fresh either, and it's very rusty, in addition to being beige.

I'm not upset about it, but I am grievously inconvenienced.

 

Hm. A bottle of Lucas and the knock is all but gone. I think I'm gonna change the oil tonight along with another bottle and see what happens... There might be some life left in it yet.

 

Crossed fingers for you

 

Took the valve covers off last night hoping to find evidence of a sloppy lifter or rocker, (and because they leaked like hell, hopefully now they don't) and I didn't find anything. Pulled the plug wires one at a time while it was idling rough, (it doesn't always) and listened... #5 didn't have much effect on the idle when I pulled it, so I checked that spark plug. It wasn't worn, but it was oily. I didn't check compression but I don't think I really need to - this pretty much tells me the #5 cylinder has a ring seal problem and that explains the occasional oil smoke and the low RPM miss.

As for the knock... After an oil change with 20w50 and 1.5 bottles of Lucas, (glad it doesn't get too cold around here) the knock has become a light tap, and it's not even constant. The previous engine in the Maverick knocked worse than this for about 10 months of daily driving before it blew, so maybe this means I can keep using the truck for a few more months while I work on getting another engine together. That's the hope anyway.

I figure with bad rings, this block will probably have to be bored in order for it to be rebuilt, and I think there are too many 350's floating around out there that don't have these problems for me be taking this one to a machine shop when I can probably get a buildable engine out of the junkyard for $2-300 max, clean it up, hone it, put in some bearings, rings, timing set, maybe pistons and a cam and go. I was pretty successful going that route with my 351w last year, and even splurging on a pair of GT40 heads I only ended up with about $1200 in it.

That's if I don't find an already built 350 (or 327, or 400, etc.) for much less, which is not at all unlikely. I got burned twice on "ready to go" engines though, so I'm really leaning towards building it myself.

We'll just see what happens. At least I have time now. (Maybe.)

 

A little update on this... I bought and pulled a running 350 out of a '94 Chevy 2500 a couple of weeks ago. Compression was ok so I left the rings alone. Crank looked good, I did put new rod and main bearings in it, and a gasket set, and of course a whole lot of cleaning. (I wonder if anyone who hasn't actually done it can truly appreciate what it takes to fully clean up an old engine...) Painted it, then started the swap last weekend.

I couldn't help but autopsy the old engine at least a little bit, and what did I find in the oil pan? A big ol' chunk of aluminum of course. It was a piston skirt. So that would account for the noise... The #7 piston was ok, but I have to assume the rings are blown out on it since the exhaust port and spark plug were very oily and the engine did have a dead miss at times. Which would account for the smoke and the blow-by.

I've only got maybe two more hours' worth of work left before I should be able to fire the new engine. I could have finished it last night but that would have meant sleep deprivation and Flowmasters at 1am for the neighbors. Will see how it goes tonight if I get time to work on it...

 

Update... And we're back to "Troubleshooting GM TBI."

The new engine is in, and except for some sort of fuel delivery problem like it's always had, it runs great. I've been all over the place in it.

But I'm still having problems. I was using all the '87 stuff, but I replaced the injector pod with the '94 part and it idles a lot better now, has more power, so that's one clue. It's not perfect, I still have to take it out of gear at lights or double-foot it, and at part-throttle cruise it gags. WOT seems ok, other than some apparent occasional spark knock. (Lean condition? That supports the fuel pressure theory... The timing is spot on.)

I've Ohm and/or volt checked the coolant temp sensor, throttle position sensor, MAP sensor and they're ok. That leaves the O2 sensor, which IS on the side where the #7 cylinder was pumping oil smoke and straight unburnt oil out the exhaust, so it's possible the O2 sensor's screwed up from that, however unless it's going into closed loop within about 30 seconds of cranking it cold, I don't think so. The O2 sensor doesn't come into play on these systems until the engine is warmed up, correct? The only codes I've read are the occasional lean or rich condition, so that tells me the O2 sensor is doing something at least.

I'm not throwing any more parts at is until I've checked the fuel pressure. I'm going to borrow a test kit from Autozone tonight, go ahead and replace the fuel filter just because, and if I don't get a consistent 9-13 PSI then I'm going to say I need a fuel pump. If I do get a consistent reading, hell if I know... I guess I'll start throwing parts at it, starting with the O2 sensor then the TPS....

 

Change the fuel filter before you do anything else...It cant hurt (the car) to change the O2s that got oiled down either. Its probably lazy now if it functions at all. If this O2s is before the converter...Pull it and drive the truck, see if it runs better...If so, the converter may be partially plugged from the oil bath it got over who knows how long. When you get the fuel presure tester...You can test the regulator by unplugging the vac hose to it, and see if the fuel pressure changes. (it should increase) If you see no change the regulator is not functioning, replace it. Also your fuel delivery problem (If it is) may be due to low voltage at the pump itself. Not unusual...Especially if the pump has been replaced. Many of the replacement pumps will have a harness plug that has to be spliced in to replace the original since the pump will be different at the plug in...Good luck man!!!

 

Alright, I got it! It runs like a new truck.

 

Well, what was it?

 

I checked the pressure, it was perfect. Replaced the fuel filter, no change... Started digging around in my box of spare parts for another MAP sensor, didn't find one. But I did find a nasty old ignition coil and said, what the hell, I'll try it. It ran so much better. Not perfect, but night and day. That told me I'd do well to go get an ignition coil, so I did, along with some spark plugs. That did the trick. It's smooth as silk, plenty of power, runs great! I'm kind of glad it took all this to get here, because otherwise I wouldn't have put those other injectors on, and clearly that helped too... I'm pretty happy. All told I still only have about $1700 in this truck!