PV9685

I posted about this last fall when I bought this car. 89 TPI 305/T5 Formula Firebird.

Car has steady misfires in idle or under light accel in gear, especially 3rd+. When disconnecting the ignition link (bypass), it appears to pretty much vanish, though acceleration is rough. For some reason the chip in the ECM is a 89 350Auto chip; and the ESC module was swapped for a 350 one, though I also have a 305 one which makes no difference.

Cap/rotor, plug wires, plugs, tried to time but it jumped a little off the mark back and forth, didn't want to touch it, looked right.

Today I checked the cap/rotor (Accell) I put them on last fall, 50 miles or less. Terminals on cap and rotor have grey/white crud. Swapped to old cap/rotor which were better.. no change.

When I bought it, I don't believe it had the mis, but during routine maint I think is when it developed. I have done the following: Fuel pressure test 38idle, when I hit the gas goes up about 5 PSI then goes down a bit to 32 then back up a little. about 43-45 engine off.

Fuel filter was replaced. MAF cleaned w/maf cleaner, swapped for new MAF(Hot Film), no change thoguh voltages were about .3v different... swapped back to old one (Bosch).

New O2 sensor.. Checked AIR injection, all is well but, it pumps to the convertor when Ignition bypass is disconnected(?). But, I removed the hose, no difference..

Compression test yielded I beleive 135 average (all close, tested with 7 other plugs in still), 55PSI dynamic compression at idle.

Coil tested at autozone as ever so slightly out of resistance. but when swapped for MSD, no change.. swapped back.

Injector resisitance was tested hot, all around 14 Ohms IIRC. Nothing out of whack.

Car runs RICH and failed emissions for well uhh, HC and NO. I cant find the report though.. Very high.

Tested sensors... Coolant temp, TPS.. I dont think I checked the knock sensor. It reports no knock even with the missed on my OTC Monitor 2000(?)

Cleaned out the top end a bit with 3M intake and throttle body cleaner.

Sprayed outer top end of engine to find vacuum leaks, couldnt find any..

When I stomp the pedal, it flies. I wish it didnt fail inspection.

ANY help is greatly appreciated!!!

-Dave

Supervisor42

You did say any help right?
Either one of the new plugs/wires is bad or:
It sounds to me like an injector is not closing off completely. That would explain the high HC reading at idle and the miss vanishing at WOT. The injector would be over-fueling it at idle and low engine speeds.
I know pulling the plugs is a PITA, but I would let it idle for about an hour, let it cool and pull the plugs. If an injector is "dribbling" the plug under it will be much darker than the rest.
If they are all the same, you can cuss me and save the cost of a set of injectors.
The only other thing that does as you describe is a bad valve seat. It will make compression cranking but no power at low rpms. Only way to find it is a non-contact thermometer measuring exhaust temps where the exhaust comes out of the head. (a good tool to have and great for grilling out)

PV9685

Leakdown test would pickup the valve seat, eh? I dont want to buy a leakdown tester... but I'm sure I can rig something up with home depot parts and my compression tester I grew up watching MacGuyver.

I just tested the EGR, no faults... I'm going to swap the O2 sensor for an old one, though I don't know how bad my spares are, I've never gotten around to testing them.

I'll see about the idling, but I gotta clean the plugs first. I had a little area on each one that was dark colored doing the compression test the other day. I have a picture of one but it's horribly blurry. Medium coloration around the tip mainly on one side of each plug. Metal ring part of plug (end of threads) is black. These plugs have seen much idling though for diagnostics.. and only like 50 actual miles.

The car gets like 8-10 MPG... Not sure how big the tank is, but I believe it only got me 100 miles. lol

And YES, ANY Help is very much appreciated, thank you.

-Dave

PV9685

BTW, last year I was leaning towards the injectors aswell, it was just a hunch. Very rich and the car had sat for about a year before I bought it. While the electrical side of the injectors passed testing, their valving may very well be in question... Though, I don't want to replace them unless I know there is an issue. I ran a bottle of Berryman's through the system last year, no help.

I'm wondering what the LBS/h rate is on 305TPI injectors? To See if I can find some replacments cheap in the event I need them.

Though the ECM doesn't pick up the richness through the new O2 sensor.. VERY weird.

-Dave

Supervisor42

You read the coolant temp sensor and intake air temp sensor with the "OTC Monitor 2000"?
They were both normal? If it's that rich then it shouldn't be a steady missfire.

Supervisor42

...And the SES light is not on??!! It does work right?

PV9685

SES light functions, car does not throw any codes.. unless I make it.

I'll read those sensor values again today and take a deeper look into them.

But, I think I am gaining some ground, what you said made me think.

I was confused at how the O2 readings were excellent yet the car runs quite rich. Well, I buy more stock in engineering/technology than common sense..

One O2 sensor, and the Y-Pipe is behind the dual Cats.. I will further inspect the 2-4-6-8 Cylinders, as they have no O2 sensor (horrible design).

Perhaps mix around the injectors, Or get one or two suitable replacements... All I have for Multec spares are I believe 14#'s (Gen II 2.8L, lol), I think this thing would be a little lean, lol.

The misfire isn't "steady" per se. It is very constant, could be two cylinders, but not every cycle. Hard to tell, but it's defenitely not one cylinder missing every cycle. Which is why I questioned the whole engine and not just a few cylinders.

I will report my findings later...

Thanks,
-Dave

Supervisor42

Diving into the injectors is a lot of work. If the plugs are uniform but all too rich, it ain't the injectors fault. Check the IAT and the CTS. If either one is reading out of the park the engine will run pig-rich.
Get a decent camera, $8 worth of Walmart plugs and do some testing.
It sounds like it's just running tooooo rich.

PV9685

BLM around 128, Integrator around 130. O2 goes super lean when pedal is pushed hard (ie: it acutally goes to .000 and in the .100's then goes to normal) When idling and brought to abotu 1500 it bounces between Rich/Lean. It reaches closed loop very easily/quickly.

Coolant after idling/ giving it a few revs and letting it even out was around 210-220 degF. MAT (I'm guessing that's the Air temp) was between 145-150 degF, ambient air here is around 77 degF.

The plugs are "new" (50-100miles, maybe 3-4 hours of idle also). But, the worst set of regular Autolite's Ive noticed. The electrodes werent very well centered over, the center pole piece. When gapping them i tried to give them a little "push" in the right direction but, I left little mars on side of the electrodes, but I dont see that causing any issues like this. I am gonna get a fresh set for diagnostics tommorrow though, why not right. I was thinkin maybe some iridium's or double platinums would help burn the mixture but, probably not.

I'll test the IAT/CTS again at ambient temperature tommorrow, once it cools. I did last year and believe they were close to spec.

Fun stuff.. lol

Thanks,
Dave

rgarcia63

if you disconnect the timing bypass, put the timing light on it, and rev and hold to 2k rpm and it jumps around rather than holding steady I'd suspect the distributor. You know without a doubt that it should hold steady, this is definitely a problem that needs to be fixed first, and may solve the other.

Regards, Raul.

PV9685

Tested timing as you mentioned. Last year I did that at arlound 1000-1200, perhaps the roughness of the engine was cuasing it to fluctuate more. But, tonight I held it at 2050 (Per OTC readout) and got 8 deg +/- 1/2 a degree in "jumpiness".

I also should mention two things I noticed. For about a minute after stratup the PCV valve (new) slaps back and forth very quickly and not totally uniformly. (Weird) Also, the engine has "no" blowby. (Good)

So, currently, I will be doing the following:

Replace all sparkplugs and idle for a length of time, checking them afterwards for buildup.

Retesting Hot and Cold resistance of Injectors.

Leakdown test all cylinders.

If it comes down to it I may remove the intake manifold and self test the injectors and see for any visibly leaks and try to get a half-assed spray pattern out of them.

Techincally, the engine should run great. LOL!

It really must be injectors/ecm, something in the ignition system, or a bad valve/seat.

I wish I had a spare computer to swap in, that would be nice.

Thanks,
-Dave