im almost done with my first ever engine swap. i replaced the lg4 witha standard 350 in my 86 camaro. problmes keep coming up, forcing me to spend large amounts of money. the latest problem is that my computer wont throw any codes. the mechanic called me just now with the bad news. he says hes checked all the soliniods, he said the computer wont ground. and therefore the car wont go into closed loop(or open loop, i forget.) and therefore it runs rich. my questions are:

what is closed/open loop?
whats a new ecm cost?
whats a new prom cost?

he says the ecm and prom need to be replaced. i have a stage 2 jet in there right now, but he says ill need sometimg different. im confused, i thought a chip was supposed to make all the necceassary changes to make the ecm work properly. i need help bad. its gonna cost me 550 bucks to make this thing run correctly if i cant get some help. i trust this guy too, my family has been goin to him for like 10yrs. please help

thanks
daniel

 

"The computer wont ground" is a pretty dumb statement IMHO (if that's what he said). If it really doesnt, then all he would have to do is FIND the ground wire and ground it! Is there a ground strap that maybe you forgot to bolt up when the engine was dropped in ? Dunno about LG4s, but my engine has about 10 grounds. LOL Most of them are hooked to the back of the heads and one in front. I'd check that first. If not... go get an ECM from a junkyard. There's plenty of em outthere, especially for LG4 cars. Also get some smaller rods for the secondaries on the Q-Jet. That engine needs more air and gas.

 

I agree with Blade. Maybe you didn't understand him, but saying "the computer won't ground" would make me take the car elsewhere ASAP!

Just a casual glance at my 91 Camaro service manual shows four wires that ground the ECM, and I would imagine that if only one of those four are grounded, it'd still work, but for reliability/stability/etc., all should be connected. Regardless, if it "won't ground", simply ground the proper wire(s) and move on.

RE the prom, I'd guess $20-30 (non-GM). You can replace it yourself (or take the ECM to NAPA/GM/etc. and have them do it, it'll take < 5 minutes).

Oops, forgot. Open loop and closed loop. Hope I remember right. The computer is in closed loop when all of the sensors are operating correctly. If one or more of the sensor(s) is bad, then the computer will go into open loop, and run the engine based on a set of parameters encoded in the computer's memory. I can't remember if this in in the prom or not. This allows the engine to operate without some (all?) of the sensors working. Until the engine is warm enough, it'll be in open loop I believe.

If I got it wrong, please correct me//tks

[This message has been edited by Stuart Moss (edited September 13, 2000).]

 

if you do replace the ecm, go with gm controller part no. 1228079 and prom no. 24502456. also shouldn't use the knock sensor for the 305. go with gm part no. 10456288 for 350. another spark control module will help also. part no. 16128261.

 

He could be talking about the Quad driver circuit within the ECM itself. It is a series of grounds that control various components, which is solid state internal component.. The ECm can be technically "grounded" meaning it has grounds going to the ECM.. but the Quad driver is failing, not grounding the circuits internally.. Also i think from what he means by no codes, might mean he cannot even communicate with the ECM.. Just a hunch, but usually when a ECM takes a dump, you cant retreive any data...

Hope this helps.

 

I would be concerned with the following:

If the car ran fine and the ECM was good before the engine swap, why is it now bad?

Changing from a 305 to a 350 should have no bearing on making the ECM go bad, not that it did not take a dump on ya...but it should still be okay, and stil operate the 350 in closed loop.

Tell your mechanic that 3 things are needed for closed loop operation...

O2 sensor needs to be hot enough (about 600 degrees F) in order to send acceptable crosscount data to the ECM.

EDIT: The above staement is not entirely correct...it's not crosscount data the ECM is looking for from the O2 sensor, but an output (350-400mv IIRC), before it is ready for closed loop, crosscounts have nothing to do with it.

Coolant temp needs to be at least 105 Degrees F as read by the CTS for the ECM (do not confues this with the temp gauge reading..it's a different sensor)

A short amount of time (about 30 seconds maybe?) needs to elapse after start up.

I'd ask him to plug his scanner in and look at the O2 mv and crosscount readings, CTS as read via the scanner.

Now, if there is no communication at all..i/e the SE light does not come on with the key, and all grounds are verified (make sure the area where they bolt to the head is not painted), have him check the bulb in the SE light...I believe (not 100% certain) that if the bulb is bad, you cannot complete the diag circuit to the ECM through the ALDL.

[This message has been edited by 8Mike9 (edited September 14, 2000).]

 

wow, thanks for all the info. i think what he told me was that he couldnt even communicate with the ECM, i ran it once for codes when the enigne was first installed, it gave me a code 12, thats it. i assumed that was a good thing cuz the manual says 12 means the diagnostic works. but then i tried it with the motor running(cuz the manual said it would work an a carb'd engine) and it gave me nothing. i didnt think anything of it cuz the manual said if nothing is wrong, no codes will flash. he said that maybe a circuit was bad or sumthin, i forget. the 02 sensor was fine, he said it had it neccessary voltage. the SE light bulb is fine, cuz everytime i turn the ignition on it comes on. he said he looked for all possible grounds for it. i thought i did too when i intstalled it. i have no loose wires or anything.

thanks

daniel

 

oh ya,

the car still runs fine, it smells real bad, like a very rich mixture. it goes and everything, it just is burning way to much gas. i mean a full tank for 60 miles. but that could be something all together new too.

 

Even if you do buy a new ECM they are ~$100 (or less) You do not need a PROM, reuse whatever you have now. This guy is either really bad at explaining the problem or a moron. If he tells you the 350 is causing your problems and you need a custom chip he is definitely a moron and immediately take your car away from him.
It sounds like he is doing the right things though. I would go through and check all the sensors. If they checked out, then i'd make sure they were getting to the ECM. If it still doesn't work. Hell, first thing i'd check is the ECM fuse (hehe, fresh in my mind from another post) with that missing/bad, all sorts of fun problems will appear in the power for your ECM.
Ask him exactly why he thinks the ecm/prom are bad. Write it down and post here and we'll tell you if it makes sense. I can't stress this enough. There are still a lot of mechanics out there who are terrified of the voodoo magic of CCCS. Even if they are a fuel injection god, something about CCCS makes them go stupid.
...ed

 

ok, i called him and he explained it to. i think this time went a little better cuz i actually understood what he was talkin about. here goes: "the ecm is not grounding its actuators, IT is grounded, the connections and all. the fuse for the accesrories is blown, when I tried to put a new one in the horn went off, and would not shut off. so i just left it out."

then i asked if all the sensors were workin.

he said "the o2, all the coolant and temp sensors have voltage and they are workin, but the computer wont ground them. thats why the SE light turns on, but wont shut off."

so it looks as if he has checked all the connections, and the fuse's.

in regards to the prom, he didnt know i had the OEM one, cuz i never told him. also cuz inside the ecm was a jet chip. so im gonna re-use the old one. he said it would be best. (saves me 70 bucks. thanks guys)

i think thats about it. so whatta ya'll think???

 

re-read my above post. I think I nailed it the first time.

2 problems... ECM IS BAD
or
Wiring harness is screwed somewhere

[This message has been edited by Kevin G (edited September 14, 2000).]

 

Couldn't hurt to undo and redo your wiring harness ground connections. Sometimes they get buggered up w/corrosion over time.