Bfenty

I'm going to start a new thread and have all of the updated information in one spot, as some other threads have gotten quite long.

I started with a misfire that was especially bad under load. I believe the misfire is in cylinders 5,6, and 7 based on pulling injectors and gasoline-fouled spark plugs. I replaced the fuel pump, spark plugs and wires, ignition coil, fuel filter. Still misfiring. Rinsed out the coolant system and replaced thermostat as well. Checked TPS setting, right at 0.54 volts.

I took the injectors off and cleaned them really well with carb cleaner. I also cleaned out the plenum and throttle body with carb cleaner while I had it apart. After this, it ran a lot better. Still misfiring, but not nearly so badly. Running on 6 cylinders consistently instead of 5, I believe.

I ran a compression test, all cylinders at 150 PSI. Fuel pressure 40 PSI. I think those numbers are pretty good. I also checked for spark, all plugs are sparking reliably and strongly.

I cleaned out the engine bay with eagle one etching cleaner at this point. I drove it for a day or two after this without much issue.

Then it started idling much higher. It had been set to idle around 700 RPM and was quite happy with that. It started running at 1100-1200 RPM, sometimes up to 1400 RPM. All this with idle screw completely pulled back. I drove it a half mile from home, turned it off, and couldn't get it to start again. It would crank endlessly but would never catch. After about 15 minutes it suddenly started right up. I drove it home.

I took apart distributor cap and rotor-both have a good bit of corrosion so I replace both, even though spark is strong. I also took out the ICM. it looks almost new but I have it tested anyway. It tests good.

Brake booster connection has a bad vacuum leak I find. I take it apart and put some RTV on it, then reassemble. Still have the high idle. I believe the brake booster is ok. I check TPS again, it's now showing 4+ volts. I disconnect TPS, which should cause the ECM to ignore it, right? Still idling high. When given throttle the engine nearly stalls. I use carb cleaner to try to find the leak, spray every connection I can find, no results. I also tried disconnecting the MAF, no change.

The EGR system and evap cannister have been disconnected since I bought it. No changes were made to either but worth mentioning. I sprayed carb cleaner into the EGR but with no effect-I don't think that is the leak.

I know I need a new TPS, odd it went bad like that. I'm running out of ideas. Help please?

EDIT: I also had the timing checked when I first started. It was set to 6 degrees. I've thought there is a possibility it jumped timing, but I think that's unlikely. I also was trying to get the heater blower to work, and found the temperature control slider to be stuck. I wiggled it a bit and it got stuck in a slightly different spot. I doubt that matters but trying to be complete, and I know the A/C system does connect to vacuum.

ls777z

I think you're supposed to use starting fluid (ether), not carb cleaner to find vacuum leaks.
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Bfenty

I would think it would do similar things. I don't have any ether at the moment.

Bfenty

Here are some photos I've taken of the engine bay.



Underneath the distributor cap



Passenger side in rear, these lines came like this.



Overview of the engine bay



Another overview



Closeup of throttle linkage



Injectors pre-cleaning



Egr valve with plenum removed

Cjunkie

Mass air flow sensor is upside down.

xrav22

Looks like he removed most of the egr stuff. Anyways this may help sort it out for hvac.

Bfenty

Yea I figured that out lol. That's is how it came though.

Bfenty

Thanks!

VikingTrad3r

Try to pinch that line and see if you have rotted cruise control lines or internal diaphragm.

Bfenty

So I'm back to not starting. I get a sputter and that's all.


I took apart and cleaned the throttle body, made sure it was sealed up tight with RTV. I also cleaned the IAC with WD40 on a rag, but I think it's broken. See video:

xrav22

I would say in this situation try the idle adjust here, this will reset to default after it is together. Your not getting gas flow from the sound of it. Remember on the 85 your fuel will get cut off by the oil pressure senders behind the distributor if they are faulty for some reason.

Bfenty

Thanks. Right now it won't even start so I can't set the idle. I agree it's certainly missing something. I don't think it's spark (unless something drastic has changed) so it's either air or fuel. I'm going to rent a fuel pressure gauge again to retest just to make sure nothing changed.

Silver85

I use an unlit propane torch to look for vacuum leaks. Works pretty well.

If you think it's fuel you might try starter fluid to see if it will run. That way you will know for sure it isn't air or spark.

Bfenty

Looks like I'm getting a drop in fuel pressure. When I turn the key on, it jumps to 50 PSI. Then it starts dropping, even with the key on. I even tried cranking it and still pressure drops.

This is new. I checked it last week and sat at rock solid 40 PSI. I can't see externally any leaks. Nothing dripping on the ground, etc.

Bfenty

Well I tested fuel pressure. It would jump up then drop off. Process of elimination (Yay FSM!) led me to the cold start injector, which I was already planning to delete. I took it off and blocked the ports. It's now holding fuel pressure but still no closer to starting. Cranks just fine but no ignition.

Next up I will check spark. I'm starting to suspect the ICM. I had it tested but I know that's not always a sure thing.

Cliff Harris

The IAC is doing exactly what it's supposed to do.

Bfenty

It's supposed to be clicking like that?

VikingTrad3r

I jumped a and B on my 87 to check, my IAC does not click continually.

Bfenty

Followed the FSM, and whaddya know, it worked! I found the ICM was bad. I had spark but injectors weren't firing. Cheap fix, unless you count the hours of labor I spent tearing everything apart...

Good thing, though-I replaced a lot of stuff that really needed replacing anyway, and learned a lot about how the ignition system on these cars works. I'm feeling pretty good about diagnosing future issues now. Thank you all for your help!

VikingTrad3r

a rapid learning curve. nice job. u deserve some great cruising.

now its time for pictures!