1987 TBI runs like crap after tune-up.

[PavementPounder]

New Delco cap, rotor, plugs, and wires. This motor has been in/out of this vehicle a number of times before I owned it and some of the wiring is "custom". Actual miles are unknown due to axle ratio, tire size, and transfer case changes over the years, but it is easily over 150k. The motor basically feels like it is missing or just not hitting cleanly. Voltmeter reads over 13v and that has also been verified to be about 14v.

The truck had been running like crap intermittently at this point. When I was able to get a second set of eyes to assist, we found that the power lead off the alternator was intermittently arcing to something in the area to the rear of the TBI on the intake. Easy fix - raided an extra wiring harness I had sitting around for some conduit, applied it to the power lead, and the truck ran much better. After finding that issue, the "ghost" in the aftermarket radio in the truck that would make it spontaneously turn on (and also intermittently shut off) also went away, so I was satisfied that we had killed the gremlin.

The improvement only lasted a few days. Truck is now running like crap consistently and even stalled three times yesterday at hot idle while sitting at a traffic light in Drive (does not stall with no load in neutral ad starts back up every time). At this point my GM Tech friend that owned it before me suggested trying a cheap fix and replace the fusable links and power lead before diving deeper and spending more $ replacing stuff.

Seems like a sane course of action to me and I'm planning on changing them today. If you were chasing this, where would you start?

 

[496truck]

Check ALL of the vacuum lines for leaks and the TBI base gasket for leaks.
Is the fuel pump on it's way out? Can you check the pressure? How does the injector spray pattern look?
Ignition wire firing order is correct? 18436572 if you don't know 1357 driv side 2468 pass side.


It's usually something simple, check the basics first.

 

[PavementPounder]

Yes, the firing order is correct. We checked that last week and even shifted everything in one direction on the distributor just for ****s and giggles.

I started suspecting a fuel pressure or pump issue after the truck stalled a couple times since it didn't "stumble out" and just spun down. That'll have to take some more investigating.

I sat there and eyeballed the injector spray pattern for a while yesterday. While I don't know what it should look like, my gut reaction was that it looked more "squirty" than perhaps it should. I know it should be a spray and not a really fine mist, but it didn't appear to be spraying very uniformally and just appeared to be a lot, which I guess would go along with the truck using a lot of gas lately. It really feels and sounds like it is missing or the mixture is wrong, as the exhaust is making a thumpy "huffing" sound as if there is way too much crap (undetonated charge) being sent down the pipes. (Sounds just like my Buell does when the FI system tries to compensate for something going out of adjustment.) The check engine light also came on a few times over the last few days, but has now stopped. Seems to happen only after you have been driving for some time. I know you can jump the terminals to read the code, but I have never done it. (Link to instructions and code table, please?)

Yesterday I pulled the power lead off the alternator and firewall and cleaned those connections well. The fusable link is not the original and still feels pliable and not brittle. I'm not so suspiciuos of that anymore. I did find one spark plug wire resting on an exhaust manifold where it made a white spot and got that zip-tied up and out of the way. (Delco wire sets that are supposed to be "OEM" are ridiculously long, BTW.)

During the past two spark plug changes over the past couple years I have owned it, the #7 plug has come out with all kinds of oily sludge crap built up on it (to the point it stopped firing), so I know there is a problem with the valve seals in that one. What I am beginning to wonder is how long it has been like that and whether the O2 sensor is also fudged up with years of oily crap being sent down the pipe. I recently bought a big-block to swap into this vehicle (someday) and it came with a NIB Bosch O2 sensor that also fits the 350 according to NAPAonline.com. I figure I might as well pull the old one out to see what it looks like and throw in the new one since I already have it.

I also now have a coolant leak at the #1 cylinder that is causing coolant to pool up on the intake, so I'll pull the #1 plug today to see if it is getting in there. Kind of dreading that. If I pull the intake off to fix the leak, I might as well tear down and completely clean out the TB while I'm at it to hopefully correct any IAC issues. Since the intake will then be off, I'm sure it will seem like a good idea to go ahead and pull the heads to do head gaskets. Since the heads would be off, I might as well take them in to be re-done with a valve job to fix the #7 cylinder and any other problems.

This is really what I was hoping to sidestep by buying the big-block.

 

[PavementPounder]

Started with pulling all the plugs last night and they were all gapped .010 too wide. No contamination in the #1 cylinder from the coolant leak, but #7 looked much crappier than expected after only being in there for a couple weeks. If this plug looks that bad in that short of a time period, I'm guessing the O2 sensor is looking pretty sorry after an unknown number of years. I didn't get the O2 sensor out last night due to the new replacement I had being the universal type that you splice in. I'm just going to go pick up the one with the correct connector already on it.

Next I unbolted and cleaned the three grounds that I coiuld easily access at the passenger front area - the one on the top of the alternator bracket, the negative cable bolted to the motor at the lower alternator bracket, and the one on the top of the frame rail. Cranking speed at startup has now increased considerably.

I also popped the distributor cap to eyeball whether it was seated correctly, etc. Couldn't find anything out of the ordinary there. Next I pulled out the IAC solenoid and found that the edge of the plunger was carboned up pretty good. It was not siezed, but I cleaned it up in case it was getting stuck and tried to clean the port with a battery terminal brush. I did adjust it a bit and the low idle speed condtion did seem to improve, but it doesn't appear to want to get up into 4th and lock up now. Have to drive it more, but probably going to adjust it back.

In the end, I didn't find the problem and it still ran like crap on the way to work in the morning. I'm dreading the longer drive to Drill this weekend and there's no way I'll be able to tow anything like this. I did buy all the pieces I need to replace the fusable links and primary wires yesterday, but didn't get to doing it.

 

[PavementPounder]

After messing around with the IAC solenoid further and making a better attempt to clean out its hole, I can now drive faster than I have ever been able to in this truck (but still not any impressive speeds) thanks to the torque converter staying locked in 4th until I get further into the throttle. Highway mileage appears to have been restored, but it still runs ****ty at lower RPM's in the higher gears.

Took my GM Technician buddy for a ride to demonstrate what the truck is doing. While the condition causing the bad plug shown above certainly isn't helping, it looks like I have a TPS that is crapping out and sending a poor or incorrect signal at the throttle range where I spend the most time. This seems to explain just about all of the truck's bad behavior, as it certainly feels like it is running on an incorrect mixture whenever I have my foot a certain amount into the pedal, but not through out the entire throttle range.

Next step is to test the TPS signal performance (or just be lazy and replace the TPS) and see if it drops off or has erratic signal areas, but new head gaskets and a new O2 sensor are now coming as well.