I am getting a code 34 in my 85 T/A, 305 TPI. I read in my other post that these proms had problems with a false 34. The only problem I am having is a very little rough. But I think is my worn out TPS. Could I be getting the false 34 and need to replace my chip?

 

I have a 85' with the 870'Ecm and I also have the false code 34
only happens if I let it idle to long. To find out if you need to replace chip open up the cover on your Ecm and see if the the code on the prom Ends in (HLK) If so you have options.

Either replace the prom with a updated one (HLM) or

Change to a 165' Ecm Or SD system.

You can get the updated prom form the GM Dealer Ship or if they are over $50.00 go to rockauto.com

Just my .02

 

Ok, thanks I will open it up tommorow and post results. Also how common is this problem and why did it happen now? Could it actually be a bad MAF?

 

According to the TSB on the false code 34, you must first verify that it is indeed a false code, in other words, follow the dignostic procedure to verify if the MAF is bad. It actually starts by saying to make sure that you minumum idle is set at 500 RPM's. If all checks out, then the updated PROM is the solution.

So, yes it could still be a bad MAF.

 

Yes I forgot to mention to test the MAF Thanks for the reminder JP84Z430HP, anyways the false code Has something to do with the fact that somany Chips in 85 Were programed with out covering the Erase Window on the chip and over time it corrupts the Programming.

 

Thanks guys how do I tell if the MAF is bad?

 

Someone told me two ways:

1. With car running tap of maf with a screw driver and if car stumbles it is bad. (was kinda weary of this one but it stumble)

2. I can't remember the Specs but test with a DVM Ask around and someone will know, Probally Grumpy would know the answer to this one. I did it like 4 months ago and didn't write it down.

just my .02

 

ok guys I got me ECM down today and here is a pic that drew with all the numbers and letter.

It says HLL not HLK

 

Hi,
I have also -85 tpi and hlk prom.I'd like to know what are fixed things HLK versus HLM prom?

Jari

 

Normally, if it corrupted the programming, the checksum would change, and turn on the SES light.

 

Well in my case if I start the car a let it Idle a really long timewith out actually Driving the car The SES light comes on and the Idle will start surging, Clear codes and then I start car with out letting it Idle but a short time I can drive for hours and no SES light, nut get caught by a Long Winded light and theres the SES light.

 

What code did it set?.
Or was it a soft fail?.

Prolonged idles will often set a 13, or lean code soft fail (ie light no code). As it first warms up you have enough richness, that the O2 wakes ups, but just at a steady idle things can do steadily lean, and then the ecm thinks the O2s died.

And if you have headers or low restriction exhuast, it can make matters even worse.

 

Well the code it sets is a code 34, I have tried a ecm from a friend that has the (HLM) and the problem dissapears also put his prom in my ecm and mine in his and He gets the same thing. so In my case I am pretty sure it is a buggy prom.

For price of the updated prom I can get a used 165' then according to Mike Davis site http://www.eecis.udel.edu/~davis/z28/ecm_swap/ I can do 10 Repinnings 1 removal, 1 addition and 2 splices and I can plug a 165' into my car. I want the faster ALDL anyways so this is the direction I am going.

 

Does anybody knows differenses between those HLK and HLM proms?

Jari

 

Here are the differences

 

WOO HOO! I got a new chip and it fixed my code 34. Still need to a little with my idle.

Thanks guys. With out this website I would have bought a new MAF and would have been SOL when that did not fix it. WOW! Somebody should inform the parts stores.

 

Glad to see the problem is solved, Where did you order the prom and How much was it. Just wondering

 

I ordered it from the local GM dealer for $71.00

 

Man, for that price you could have upgraded to the faster '165 ECM.

 

my prom says:

Delco
FTN
9550

980
1603 2500
M8451 00106

Iv got an 85 Trans Am w/ 305 TPI and swapped a 350 keeping the TPI but it wont start..it turns over, has fuel pressure

What Prom do i need or what ECM's can i swap in with no modifications that will run my 350

 

Ok when You Kept the TPI did you Buy Larger Injectors or are you still running the 19lbs 305 Injectors.

1985 There wasn't a 350 Tpi available only a 305Tpi For a Trans am And for a 350 with the 1985 870' Ecm Your gonna need a Prom from a Corvette.

Your options are:
Ac Delco # 16052307 4-SPD M/Trans (MH5) 2308HLS www.rockauto.com Price $43.99
Ac Delco # 1227805 4-SPD A/Trans (MD8) 3200HLH www.rockauto.com Price $50.79

Not Sure But You might also need the calPak. At the botton of this picture Link Provided By Rbob are what the prom and Calpak look like for a 870' or similar ECM


If ya need the calpak the Ac Delco # 16042430 for $18.57

If you are serious about tuning your car and want to learn I would recommend looking in to the Swap form the 870' to a 165'

Check out the details on the swap at Mike Davis Site here Mike Davis 870' to 165' Swap

 

Yes i put 24lb. injectors in

well for now i just want to get this thing runnin so im not planning on going to the newer computer until later


So for now which one of those proms do i need and also what is the part number for the calpak

I have an 85 t/a TPI 700r4 auto trans

 

No calpac in the 870 ECM, that part is actually built into the computer.

If your 350 won't start on the stock prom you may have other issues. I ran my 350 on the stock 870 & 305 prom for break in of the cam and for the first 500 miles. It would start cold just fine and needed "help" to start when warm.
You need to hit the basics, are the injectors firing? Is there a nice hot spark? If it won't start you are missing one of those two.