I have a 1984 Trans Am. It had a carbed 305 H.O. originally. I bought the car a year or so ago, from a guy who had swapped in a 350 T.P.I.. 1988 I was told. He replaced the computer, and fuel pump, those are the only things I'm sure of. Since I've had the car it has been a real fight to get it running right. Things I've replaced: Fuel pump relay, MAF, CTS, Oil pressure guage, TPS, Coil, Distributor, Cap, Rotor, Plugs, Wires, Thermostat. The problem I'm currently trying to fix is no timing advance. I set it to 8 degrees btdc with the est wire unplugged (the timing mark jumps around by 2-3 degrees, only holds steady when car is in high idle) plug est wire back in and no change. No advance, no retard. The only thing left to replace would be the ESC module. My question is - Does anyone know how to tell the difference between a 305 and 350 module? The number on the module I have is HKM 882401 (Niehoff). The cheapest one I can find here in Missoula Montana is $85.00. I would hate to throw that money away if it is not the problem. Any advice/knowledge would be appreciated. Thank you, Sonny.

I don't think there is a difference. The ECM controls how much advance the engine gets, the ESC simply makes it happen.

When I look the parts up at parts america they give different numbers between the 84 carbed and the 88 TPI. But the pictures are exactly the same. Not to mention the 30 dollars difference in cost. I read somewhere else that the 305 and 350 ESC will not interchange, but nothing on how to tell the difference. The niehoff model number on my current ESC does not come up anywhere.

The ESC module is used to retard timing when knock is detected. If you are not getting knock retard then the ESC module/knock sensor is not the culprit. You'll need to datalog to see if there is retard, or, you could disconnect the module, ignore the code, and see if your timing is still jumping around by using a timing light. If no longer jumping around, reconnect the module and disconnect the knock sensor. If not jumping around then it's the knock sensor that's bad, else the module.

If you want to insure proper knock retard you should buy the proper module for your engine.

Well the carb ESC will be different, the distributor is different. 84 will have the cap-in-coil HEI setup, 88 will have the remote coil. However the ESC between a 305/350 TPI should be identical.

Theres a difference in the 305 and 350 TPI ESC module, different numbers on them, and as same with the Knock Sensor, 305/350 TPI KS is different too, because they are tuned to the block size...

So if you got an 305 buy an 305 module and if you got an 350 buy an 350 ESC module, tpiparts sell them both..

I think you are confusing EST and ESC modules. ESC modules are either mounted on the firewall or inside the MEMCAL but never in the distributor, that's where the EST module is found.

EST - Electronic Spark Timing - controls timing
ESC - Electronic Spark Control - for knock control

I should have mentioned earlier that the EST module is likely the culprit but by eliminating the ESC/knock sensor as the problem (which is easy to do) pretty much narrows it down to the EST module (or ECM).

Maybe I'm confusing you guys. I have no spark advance. I set the base timing, with the black/tan two wire connector unplugged. When I plug the wire back in the timing should advance right? Well it doesn't, it stays at base timing. I just replaced the distributor this morning and while the car doesn't seem to miss as much, the timing still does not advance as it should. Or at all for that matter. Hope that helps you to help me. Ask any questions, I will answer. Thank You, this site has been such a huge help to me with this car so far!

First of all i think you need to find the correct connector. The set timing connector should only have one wire,a black and tan wire. Have you verified the check engine light is functional and no codes are saved in memory?

Yeah, you're right. I was thinking the ESC was the module on the distributor base.. Dang confusing acronyms!

Easy to do, especially when there is only one letter difference and they both have to do with timing.

The check engine light is operational. I get code 12 three times followed by whatever codes are stored in memory. Now....if there are codes stored in memory will that effect normal operation? If that is the case maybe that's my problem. But I thought that when the problem was corrected and the light turned off, everything would operate normally. As far as the set timing connector, in addition to disconnecting the two wire connector(which made no difference at all) I jumped terminals a and b of the aldl while the engine was running and It caused the timing to jump up about 5-6 degrees. Is that normal? Also when I rev the motor slightly the timing retards 6-8 degrees before coming back up to base. The motor that is in there now is the 88 5.7l TPI. And I think it indeed uses a two wire set timing connector.

Is the EST the same as the ignition module mounted on the Distributor that has one two pin connector and one four pin connector? Because that was just installed this morning with the new distributor.

Okay, I feel like an idiot, but hopefully learned something valuable here. I do have timing advance. I was disconnecting the wrong wires to set the timing. It is indeed a one wire connector black/tan. Thank you all so much for pounding your brains along with me here. If I run into any more problems I am thankful I have your knowledge and experience to rely on. Many many thanks! Sonny

End Thread.

Missoula Montana,

My home town, boy I'll bet its changed over all
these years

Still have the pulp mill odor?

Later

Hey, did you find if the HRK 882401 esc module is for a 350? They are different from 305 to 350's I need one because I changed my 305 for a 350 and found one with hrk 882401 on it and want to know if that is for a 350. Do you know???

The correct ESC's are:

5.0L: HKM -2391
5.7L: HKR -2401

The HKR was also used on the 4.3L V6's.

RBob.