Magnum '82

I gave up and took my '82 to the Chevy garage to have them try and solve the rough idle(warm) problem. Ignition checks out. Tech balanced the air flows- they were only off a very slight amount, so he doesn't think that solved anything. He feels that it is a fuel/air problem(the engine will shudder intermittently). He told me GM had updated the prom years ago because of an idle problem, BUT in doing a nation-wide search, they could not find any updated PROMs. Does anybody have any ideas for a cure or a replacement PROM. I'm about ready to run this thing off a cliff! :mad

WashingtonRacer

He couldn't plug into a diag port? I don't know the pins, but you should be able to use a multimeter to read the trouble codes, if there is any.. the needle would sway a certain number of times then stop. You count those numbers. Then it will sway again, you count those numbers, put them together and that would be your code. Have you tried disconnecting the battery for about 15min, this should effectivly reset the ecu. and it will begine to gather information over again. If the problem remains there right when you re start it, it may be a faulty ecu, hard to believe though. If it stays away for a little while then comes back, move onto the sensors. Have you inspected the O-2? Personally that would be the first place I woudl look. It sounds like perhaps it's finally kicked the dirt, and sending faulty readings back to the ecu. this would cause what your explaining. Another possibility would be the ATS "air temp sensor" or Air flow sensor. "what ever kind you have". It may be a good idea to post on the engine mods and even the C-4 side. You will run across, well practically everyone over there is injected in some way or another. They may be able to point you in a much better direction.

Jim Martley2

I can send you the original PROM from my 82 if you want to try it. I put in a Hypertech PROM in it right after I bought it to cure the early converter lock up problem that all 82s had. Let me know.

MN-Brent

Here is the GM service bulletin:
**************************************** *******
PROM UPDATE FROM GM FOR 1982
1982: Service Bulletin: Spark Plug Fouling/Driveability Improvements
Subject: SPARK PLUG FOULING/DRIVEABILITY IMPROVEMENTS - 1982 CORVETTE WITH FEDERAL EMISSIONS
Model and Year: 1982 Corvette with Federal Emissions
Source: Chevrolet Dealer Service Technical Bulletin
Bulletin Number: 82-T-101
Number: VIt
Section: Aug., 1982

TO: ALL CHEVROLET DEALERS

A new PROM has been released for the 1982 Corvette to reduce the possibility of spark plug fouling and to enhance driveability. This new PROM leans the fuel calibration during cold engine operation and unlocks the torque converter at a lower throttle opening.
NEW ECM 16029531
PROM Identification 391A36
Service Prom 1226096
In addition, check spark plugs for fuel fouling and replace if necessary. Use care when removing spark plug wire boots from spark plugs. Twist the boot one-half turn before removing, and pull on the boot only to remove the wire. Check to make sure plug wires are routed correctly and through the proper retainers.

Use applicable labor operations
**************************************** **************
Good luck finding the chip.

Brent.......

Magnum '82

WashingtonRacer- I am not getting a "check engine light", it just runs rough when idling. I just put in a new Bosch 02 sensor, new plugs, new plug wires, dist. cap, and MAP sensor. Tech says the dist. is right on the money. :cry Thanks for the tip on the C-4 site- I'll run it by them.


[Modified by Magnum '82, 7:59 PM 9/17/2003]


[Modified by Magnum '82, 7:59 PM 9/17/2003]

Magnum '82

Jim Martley2- Thanks for the PROM offer(no guys, he did not ask me to the Prom) I will see if mine has the updated one in it already. If it does not, I will take you up on your offer. Very much appreciated.

Magnum '82

MN-Brent- Thanks for the PROM info. Now I can check to see if mine was updated.

Skyhigh82

Will the O2 sensor cause that much trouble? I've been trying to tune my 82 for the last week without the exhaust on, straight OEM headers. I’ve got a similar rough idle problem in that I can’t keep it running to get a timing light on it.

Enad

Have you checked your EGR valve? The ECM opens it only after the car has warmed. Easy to check. Pull off the vauum line and plug it with a golf tee or other Bubba tool. See if idle improves.

Other than that almost all of my problems have been related to vacuum leaks.
I've heard a bad PVC valve can affect idle too.

Dane


[Modified by Enad, 8:04 PM 9/17/2003]

Desertdawg

If all its doing is a shudder during idle, then you have nothing to worry about, it fuel puddling in the intake mainfold. If it's more than just at idle, then your losing vacume somewhere.

Have you asled at the crossfire forum????
http://www.crossfire.homeip.net:81/

Magnum '82

Desertdawg, is there a cure for this puddling problem?
PS: I tried to get on the X-fire forum and it wouldn't work for me with my old password. I'll have to try again when I can find time.


[Modified by Magnum '82, 8:26 AM 9/19/2003]

Desertdawg

The puddling problem is just something we have to put up with, but it sounds like yours is a little worse than normal.

I am not an expert with the crossfire, I just have lots of useless information stuck in my head. That's why I suggested the crossfire forum.

Unless we can get Marck (Twin Turbo) to chime in here.

Twin_Turbo

Hey guys,

If you want a pass, email me and I willsend you a new one, no problem (I am the admin of that crossfire bunch :D )

As for your problem.

Have you checked the fuel pressure? If it's low you will get poor atomizing.

Also, the PROM should not matter, revision proms are only for curing the annoying TCC lockup in lower gears, nothing else.

Have you cheked the coolant temp sender? When it's bad it won't trip codes but the eninge will run very poorly. Replace w/ alter (85 up) style connector with weatherpack connector if the stock mushroom type thing is still on there.

Check all AIR checkvalves and switch valves, could be an exhaust leak too.

What is the MAP reading? Is it steady? Is the MAP hooked to manifold vacuum and not venturi vac (center port) What kind of hose does the MAP have on it? A thick plastic line (almost hard line) works best, some robber hoses pinch and will give an oscillating signal (hunting idle) from the hose collapsing and expanding.

There's a diagnostics connector under the ashtray, it's standard ODBI, any shop should have a scanner for it. If not, build your own: search for WINALDL by Jonas Bylund.

To check codes ground the test & ground leads on the connector. There are 2 rows of pins, one row is fully occupied, the other row isn't

It looks like this:

[07][08][09][10][11][12]
[01][02][03][04][05][06]

01=ground
02=diagnostics
03=air
04=check engine light
05=serial data
06=tcc lockup
07=n.u.
08=n.u.
09=n.u.
10=n.u.
11=n.u.
12=fuel pump relay

Is the EGR working properly?
Do you have vac leaks (also check vac booster, headlamps, cruise control transducer and vac. disconnect switch behind brake pedal), heater vac.


If you suspect the ecm and prom, you can try a 84 auto ecm and the corresponding prom, that one is plug and play and improves idle and response a bit



[Modified by Twin_Turbo, 5:19 AM 9/20/2003]

CWUin82

Jim,
Can you give more info on the Hpertech PROM?

Thanks,
Jim

Pete Z

I had that same problem when I bought my 82.
Turned out to be the coolant temp sender.
Marck replaced it for me with a C4 sender,and it runs smoothly for 18 months now... :cool:

Jim Martley2

The Hypertech ThermoMaster PROM allows you to run a 160degree thermostat, cranks in a little more agressive timing advance curve, richens the fuel a bit and gets rid of the damn "30mph locking Torque Converter Chuggle" that was driving me NUTS!!!! It was worth the $130 I paid for the chip just to get rid of THAT!!! :) :) I have since installed 2 in other 82s and Guy Wright (aka: 82-GUY on this and other forums) has installed them in BOTH of his 82s and he is happy with the differance in the cars performance & drivabuilty. DO NOT but it from Ecklers!!!! Call Summit Racing in Ohio. They give abiut the best prices I have found.

Jim


[Modified by Jim Martley2, 2:09 PM 9/20/2003]

Twin_Turbo

160 stats suck, the ECM will needa CTS signal for 172F to go into closed loop. If you have a low temp stat and the cooling capacity to have it actually run at 160 you will be in open loop, it will start to switch back & forth. Most of the cooling systems however are not adequate to cool it to 160F so the colder stat is plain useless.

Magnum '82

Glad you mentioned the thermostat. You guys are hitting on all sorts of stuff for me-thats why I like this site. I installed a 160 degree thermostat years ago when I installed the underdriven pulleys. Although it normally runs about 190-200 degrees all the time. UNLESS I get on it WOT for some distance and then pull in the driveway without some cool down time. Then it will warm up higher(like 210), due to the underdriven pulleys I suspect.


[Modified by Magnum '82, 11:27 PM 9/21/2003]

Magnum '82

WashingtonRacer- Are you by chance a member on the RSWARRIOR.COM site?