NoTransistors

As some may recall, I have had an issue with intermittent rich idle in closed-loop mode.
Because the weather has been getting warm, I figured that it is time to pull the tamper-plugs, and adjust the carb, using the guidelines supplied in past postings. My plans were for this weekend.

I do need to go back to last fall, to present to you the reason for this post:
Last fall, I rebuilt the carb, but failed to fix the rich issue, because I did no re-adjustments. But, I did replace the T.P.S. This replacement got rid of an odd, intermittent engine clatter that had been irritating me for years, as no one was ever able to trace it.

Well, that noise returned tonight. I recall reading that some of you have had no luck with your TPS replacements lasting. I assume that my TPS is again busted. So, who sells a decent part? The present one is Standard Brand; is KEM better? Does the dealer have better parts? Please advise. I still plan to pull the carb, and it would be great to get a quality TPS 1st.

Seth

phess11

Dealer should have good parts.

naf

iTrader: (7)

Good to see you working on the car again...that didn't come out right. In a perfect world we'd never have to chase down gremlins, we'd just spend the weekend polishing our engine bays.

Anyway, can't really help on the TPS. I've read too many different opinions on what's best, what's not, this one's made by the same company...

Just wanted to say good luck, need anything just ask.

Mike

NoTransistors

Thanks, Mike.
Gone forever, are the days of simple repairs.

Seth

NoTransistors

So, are we still looking at the carburator mixture screws, or is the issue somewhere else? Read my observations, please.

I have yet to pull the mixture screw plugs.

I had nothing to do a few afternoons ago, so I tinkered with the air-bleed screw while the engine was hot. Carb leaned out; engine smoothed out. Exhaust stopped stinking. The next day, the 1st few blocks of driving seemed sort of lean [bogging slightly under lead foot].

Just now, I warmed the engine, then checked mixture solenoid dwell. Way too high at 38 degrees. Adjusting this screw has a huge affect on mixture [my nose and ears say so], but dwell stays at 38.
Nothing I did could change the dwell. Pulled O2 sensor. Nothing. Pulled computer temp sensor. Two degrees. Pulled TPS. Big change. Pushed down on steel dowel that resides over TPS. Nothing. Am I even going into Closed-Loop? Interestingly, the dash temp guage is way below 190. Let us say that everything is capable of working properly. Do we need 190 degrees for closed loop?????? Or, is it time to find a computer and chip?

Are the mixture screws still the obvious next step?
And is a new thermostat a good idea?

Thanks,

Seth

naf

iTrader: (7)

For closed loop you need to satisfy both the CTS (not sure if it's 190 or not) and have a signal from the O2 that the ECM recognizes. You'll know it's truly closed when the dwell ranges and changes with IAB adjustment. If the CTS is satisfied but the O2 signal is not close to what the ecm expects, then the dwell may change with TPS position but there will be no ranging (needle bouncing) and the IAB will have no effect.

Turning IAB out allows more air into mixture, leaning the engine, but it's purpose is not to set idle mixture but to provide a mid-point for the dwell so the ECM has the most flexibility in mixture control.

I would make sure you're getting it hot enough to satisfy CTS then open your mixture screws if you're still not getting a change to dwell with IAB adjustment.

NoTransistors

Last fall, I purchased a Bosch replacement O2 sensor. Installed it, got same results, and put old one back. Now, where did I put that new sensor? Like that would solve this problem. Engine presently has new TPS, new computer temp sensor, new vacuum sensor, carb rebuild, plugs, coil, h.t. wires, intake gaskets, and perhaps a few other odd things.



Edit: found lost sensor and replaced. No difference.

Seth

NoTransistors

I pulled those d**n near impossible mixture plugs, leaned the screws a little, piddled with the solenoid stops. The point is that nothing can make that dwell needle budge below 38 degrees on six-cylinder scale. The air bleed smooths out idle, but still the meter doesn't budge. Pull the O2 sensor, and nothing, etc................................................................

I bet the next time I use the car, cold running will be stumbly and lean, as we will be starting out sort of lean.

Computer or chip or perhaps gremlins? If the experts in this group lean towards electrical, rather than mechanical issues, someone out there in ThirdGen Land must have the appropriate spares to sell. Would be wonderful if it falls into place so simply.

HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Thank You,

Seth

trumps2000

iTrader: (2)

I think I may be having a similar problem. I tried tuning the Qjet with minimal results. At one point I thought I had set the dwell to ~30 degrees but sometime later it was still fouling plugs left and right, even though it hasn't left the driveway (not on the road yet). I just got done replacing most of my igntion and now it runs completely lean and no amount of moving the IAB or mixture screws did anything.

I too have a 180 degree thermostat and now I'm wondering if the computer is ok running the engine 20 degrees cooler. I've noticed a lot of the chip companies state that its designed for a cooler thermo:

"ThermoMasters contain special programming that allows the use of a 160-degree or 180-degree thermostat."

Hypertech, Inc.

Does this mean the stock chip won't quite work right? I'm thinking about wiring a resistor in series just to fool the computer. At some point it'd be nice to install this 8079 ECM with a modified ZZ4 bin.

NoTransistors

I put in a new 190 degree thermostat, late this afternoon.
Seems that with the Redline 'Water Wetter', mixed into the coolant, the car needs to be driven to achieve enough heat to open the thing, when the weather is in the low 70's.
Driving home tonight, I noticed that the idle 'hunts', when in neutral. NEVER happened before, not even after tinkering earlier in the day. Perhaps it is working again, after a year of opened-loop? Not a clue, as I am now going to sleep.

Nice car show tomorrow, right here in Brooklyn.

edit: I once tried a 180 degree thermostat. Engine still found closed-loop, without any issues. The chip is original G.M..

Seth

naf

iTrader: (7)

An LG4 that doesn't run a little hot? I think you're there with the higher t-stat. Let me know how it goes.

NoTransistors

New thermostat maintains a nearly-two-hundred degree temperature, but has done nothing to bring me closer to closed-loop nervana.
I will try to get the flex-wrench for the mixture screws, but at this point, it seems unlikely that this is the issue. More and more, the computer or chip seem to call out the words, 'replace me, replace me.'

Seth

naf

iTrader: (7)

Mixture screws are the next most likely and least expensive (time and money) item to check.

Have you re-verified 1/8" of travel for the MC solenoid with the carb on the engine? I had one once that was bench adjusted then the hat and one of the primary rods hung up once it was hooked up. Played heck trying to figure that one out until I noticed it wasn't clicking. It's easy enough to check by pulling the IAB screw out and measuring with a secondary rod. Kinda unlikely, but I'm throwing everything out there.

You can also take it to a tune up place and have it hooked up while running to see what the ecm sees. That will let you know if all your sensors are sending good data. Might also tell you if the ecm is bad or not.

I'd play with the mixture screws first though.

NoTransistors

The solenoid stops are way out of adjustment, because I did fool with them, without any regard for proper settings. Thanks for letting me know that travel can be checked through air bleed screw hole.

Think I know where to get the mixture wrench. It was not included with the carb wrench kit that I use for the TPS and solenoid stops.

Also, I need to replace the recently-replaced TPS, as the intermittent tapping noise is definitely back. It disappeared completely with the new TPS , last fall, after bothering me for years. This issue is not any carburator adjustment, though it may not be the TPS this time, but the computer or chip.

Thank You,

Seth

99Hawk120

The ECM will go into closed loop somewhere between 120 and 140... I can't remember the exact temperature offhand, but it's WAY lower than even a 160* thermostat.

naf

iTrader: (7)

I have had trouble with a 160 before. Lost lockup intermittently (probably as tstat opened). I never verified temps but replaced with original 190 and the car was fine. 120-140 sounds about right though.

NoTransistors

With the new thermostat, I still do not achieve closed loop. The carb is set lean enough; so lean that ice-cold running now includes some bogging. It is not the carb. Also, the mysterious, intermittent knock seems to be back for good. If I did not know that bad computer timing could logically cause an intermittent knock, I would blame the noise on a bearing.
So, who wants to trade a working computer and chip for some green? Part # available upon request.

Seth

NoTransistors

I hate to beg for tech answers, but obviously, an answer still needs to be given. Carb is certainly leaned to the max, so am I looking at the computer, or a chip? Anyone have a set in their spares drawer? I know, I know, "Go to the classified section of this web group".

Seth

trumps2000

iTrader: (2)

Have you tried Ebay? I've found a couple of them there.

NoTransistors

There is nothing on eBay at this moment. My plan is to get a computer, and a chip, even if they need to be sourced from different dealers.

If these parts get the engine back on track, then the next step is to secure a different carburator, of the same model number. Why, do you ask, does Seth need another carburator, even though he did a decent rebuild?
The answer is I still have an occasional issue involving a run-away carburator. No, the throttle cable does not get stuck. It is possibly as simple as a leaky choke pull-down, but I am very tired of this dangerous problem. If it wasn't for N.Y.C. emissions, I would go for a Holley, Mallory, and the few other parts required to get this crap out from under my hood.

Sad thing is that this lean-burn type system works well, when it works.

Seth

naf

iTrader: (7)

I've suspected that your run away issue could be related to worn throttle bores. You could sleeve them but would probably be more comfortable with all new stuff that you know is good. Sorry to hear about the ecm, I could get you a price on a JY item here if you wanted to go that route. There's a yard a few miles from the house that specializes in camaros/firebirds, fact I could forward their e-mail address if you want, they can ship as they do e-bay.

Mike

NoTransistors

People are so very nice here.

If I go the JY route, I can save on the price of an after-market chip.

A genuinely-new computer-controlled carb from that popular ebayer would be $305.
The JY computer with chip would still keep the price within affordable limits.

To fix the car with non-emission parts, I need to figure in a carb, a spread-bore spacer, a Mallory distributor, a B&M lock-up kit, a kit for connecting the pressure cable, and finally, double-price for each 'special' inspection. And, what if those guys are forced out of business? Proper emissions is indeed the cheapest route.


So, Mike, PLEASE send that E-Mail link to NoTransistors@aol.com, at your convenience. Once I get closed-loop, I can order the new carb.

Thank You Again,

Seth

trumps2000

iTrader: (2)

NoTransistors, I do have an '86 ECM I bought from Ebay if you want it. I bought it for troubleshooting too, but I don't think the ECM is my problem and I could use the $ for the frontend rebuild. $30 shipped (as-is of course). I live in north Jersey so I think you could expect on Saturday if I ship it tomorrow.

NoTransistors

Trumps2000

I appreciate the gesture tremendously.
As your chip is possibly different, I will still need to get one. So, I will get back to you on this generous offer.

Seth