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'87 350 TBI having troubles

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Old 01-08-2013, 06:58 PM
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Default '87 350 TBI having troubles

Well, I have had several issues with this engine since I bought the vehicle, and I've slowly been fixing them. First, the rubber hose in the gas tank was broken, so I wasn't getting proper fuel pressure. After that, it seemed to run fine, but smoky, so I replaced the PCV valve and line, and that fixed that. A new oil adapter gasket set fixed the oil leak (I actually still have a leak, but I think I just didn't tighten the bolts down enough).

After dealing with the steering box replacement, I noticed the engine would backfire occasionally, something it hadn't been doing before. I tried checking the timing, and after disconnecting the computer timing adjust wire, the thing ran like complete crap. When first started, it can hardly hold an idle. After warming up, it holds idle fine, but it idles very rough, and is pinging left and right.

I also seem to be having trouble either with my light or something in the ignition line, as the thing doesn't want to flash consistently. My timing seems to be at the 2 degrees mark, which isn't too bad.

Now when I reconnect the wire, besides the fact that I can't get the timing gun to flash at all, it seems to run rougher than it was before, and it was backfiring quite a bit before.

I'm hoping somebody has some idea what has gone wrong now...
 
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Old 01-08-2013, 09:08 PM
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It has been suggested to me that its possible my balancer has slipped, and so the timing is actually quite off. I will check that tomorrow.
 
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Old 01-09-2013, 09:54 AM
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Have you checked for broken or cracked vacuum lines?

Maybe I don't understand but you can't get the gun to flash? It's hooked up to the #1 plug wire, correct? Unless the plug is disconnected at the cap you should be getting a flash.
 
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Old 01-09-2013, 12:42 PM
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I think the issue with the timing gun is that it can't handle the RPMs for some reason. When the engine is idling slowly, it works sporadically, and when the idle is faster, it just doesn't work at all. The slower the idle, the better it seems to work. I'll try and get another timing gun to try.

As for the vacuum leaks, I'll check for any. I am curious though, on my throttle body, I have two lines that have just been plugged coming out of it. The first is on the front of if, and I believe its the one marked A, shown to return to the fuel tank on the timing/vacuum diagram on the truck.

I tried finding TDC, but with the tools I have, I only have a rough idea of where it is. I stop getting blowing from the spark plug hole when the TDC mark is around the 12 degrees mark, but I have no idea if that is accurate or not.
 

Last edited by bman22; 01-09-2013 at 01:52 PM.
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Old 01-09-2013, 08:05 PM
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I did find a vacuum leak. Plugging it helped a little with the engine running properly. It now idles a tad bit slower and isn't running so rich. It still pops and bangs occasionally though. I tried a compression tester to find TDC, and it seems like it agrees with my guess of 12 degrees. Either way, that much of an advance shouldn't cause problems should it?
 
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Old 01-09-2013, 09:04 PM
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Run a compression test on all cyclinders possibly you have a burnt or a valve thats stuck open which would cause backfiring and running with a very bad mis.
If yout timing checks out to be ok the pinging you hear could be from a bad knock sensor.The knock sensor is also related to your timing.
 
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Old 01-09-2013, 10:13 PM
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I thought I'd clarify everything I've noticed so far. First off, the backfiring and such is not frequent, it only pops occasionally, and it has no trouble keeping idle while the EST wire is plugged in. It does hunt within 5-10RPM as it warms up, but I assume that is normal as it goes into closed loop operation. It also seems to be running at a high idle, as when it is put in gear, the whole vehicle slams, and it sounds a little fast to me.

When I unplug the EST wire and try starting it, it runs very rough. At first, it has trouble keeping an idle, and nearly dies two or three times before it is able to keep an idle. It hunts within the few RPM quite a lot, and I can hear lots of pinging and knocking from the engine. The timing mark says the engine is timed at 2 degrees advance, but I don't know if the timing mark is accurate at all.

Now, when I have the EST plugged in, if I rev it up, and let off the pedal quickly, it backfires quite a bit, not just the popping I've heard on 350s revving down. Revving it up with the EST wire unplugged produces a lot of bad noises from both the engine and the exhaust.

During normal running, I get a tiny bit of light colored smoke, only really noticeable if looking closely, along with a gassy smell, suggesting it is running rich. The one plug I have pulled doesn't seem fouled, it looks quite clean, but has some brownish residue on it. I don't have a catalytic converter if that makes a difference.
 
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Old 01-10-2013, 09:04 AM
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The balancer cant slip theres a lock on the crankshaft and a notch on the balancer that holds it in place.Now your timing chain may have jump a tooth or two but I would try by replacing the knock sensor.Its on the drivers side of the engine block.When it detects the engine ping it tells the pcm to retard the timing.Did you take the distributor out and put it back in?If so maybe thats off and thats why the engine cant be timed.Also have you disconnected the battery to clear the pcm?Try doing so so it can relearn the sensor functions.This year engine is rather simple to work on since it was in the early days of computerised engines from GM.
 
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Old 01-10-2013, 10:09 AM
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The balancer CAN slip, It is two pieces of metal joined by a rubber isolator. The outer ring can slip...

What do you have the timing set at with the dst unplugged? Should be 0.

If your timing light is not flashing then there is a weak ignition signal traveling throught the spark plug wire. Start there, checking your connections. Are all the plugs tight on the cap?

Has anybody messed with the O2 sensor? I mean do you have headers and the sensor is just dangling in the wind?

Have you tried pulling codes out out of the ecm? Plenty of discussion of how to do this on OBDI systems.
 
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Old 01-10-2013, 01:34 PM
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The mark (if it is accurate...) is set at 2 degrees advance. I'd try adjusting the timing, but I have next to no access to the bolt for the distributor clamp, and I have been unable to get it free so far. I even lost one of my sockets somewhere on top of the transmission trying to get it free.

The timing light is an old cheap thing, one that goes between the plug and the wire, it might be the gun, it might be the ignition. I've been meaning to get another gun to test that.

No, I have the original manifolds, and the O2 sensor is still in it. I pulled the codes out of the ECM once before, and they were related to the fuel pressure issues I was having. I don't think there are any set right now. I'm going to try and build one of those ALDL cables and use WinALDL to see what is going on.

As for resetting the ECM, I disconnect the battery every time I finish working on it, as something in the vehicle seems to drain it if I leave it connected overnight.
 

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