wierd problem - NJFBOA - Home of New Jersey's Camaros and Firebirds

z28camaro94 · 08-21-2012, 08:57 AM

Towards the top of 2nd gear it made the most god awful bang. after which the check engine light came on and the rpms dropped to idle and when hitting the gas the rpms didnt change. pulled over, shut it off and when started back up i had no oil pressure. so at this point i start panicing. shut it back off imediatly. checked the oil on the stick, up to level and no shavins that i could see. let it sit for 5 mins, started it back up and ran fine. no check engine light, oil pressure fine. it was a lil down on power but nuthin crazy, and it was putting a lil when crusing. took it home and let it sit for the night. next day checked fuel pressure( thinking the bang was a serious predetonation) but fuel pressure checked out to spec at koeo and koer and didnt bleed down upon shut off. so i decided to drive it a short distance around town. somethings making a buzzing noise only when in drive and theres a load on the motor. in park or neutral and revving up a lil the buzzing is not there. i have not yet dropped the tranny pan to see if theres any metal in the tranny. the tranny was rebuilt 15 k ago, with hypo ****, beast sun shell, alto red band, 7 cluthes and steels per pack, upgraded servo, no shift kit, and 2500 stall. have taken it to the track and put many passes on it without problems. it still shifts through all gears when it should and how it should.

so im at a lose for what it could possibly be. anything i could do or check or any insite on this would be appreciated.

didnt mean to post twice, internet acting up

The_Bishop · 08-21-2012, 09:24 AM

Sounds like it may be tranny related.

SRGN · 08-21-2012, 10:26 AM

Might want to see what the history code is that is stored.

z28camaro94 · 08-21-2012, 11:06 AM

the problem with that is theres something wrong internally with the comp....i cant scan it. tryed....ohmed out the serial data line and its good so its internal...i have a nother comp but still need to get it flashed

SRGN · 08-21-2012, 11:23 AM

I'm inclined to believe transmission related as stated above. The code would probably be helpful in diagnosis if it was accessible. If the PCM is fried, it could also start firing shift solenoids at the wrong times and really cause some damage. I'd take care of that before moving any further or even driving the car.

z28camaro94 · 08-21-2012, 11:45 AM

the car has been driven for 12 yrs wit the comp problem....no drivability issues and the tranny still shifts when it should and how it should(firmness), it doesnt go in and out of gear and the converter locks up like it should. i no i need to fix that first just need to flash the new one i have. just weird that it would happen now after all the driving that has taken place...as i said it was rebuilt 15k ago but that also was like 8 yrs ago

SRGN · 08-21-2012, 12:52 PM

It could also be finally giving up the ghost, or may be what contributed to the initial transmission failure.... Have you checked for ripple/AC voltage in the system from a failed rectifier bridge in the alternator? Can cause some strange issues, especially under a high electrical load.

z28camaro94 · 08-21-2012, 05:15 PM

the initial trans failure was from racing it at cecil. lost 2nd and 4th. i have not checked for ripple. that is a good idea considering its the original.

thanks for the input, at least i have some ideas what it was. still dont know y it would lose oil pressure like that, then come back. or y when the rpms dropped to idle and stayed there even when given gas.

ima go check now if i can find my multimeter. ill keep it updated

z28camaro94 · 08-22-2012, 04:58 PM

so the alternator is putting out 30vac...im under the impression that its only to put out less than a volt. and thats at the battery and at the alternator...so ill replace that next

the tranny is still making that buzzing noise...but only in drive and reverse...im goin to assume that i hurt the tranny....great 1800 that i dont have

Featherburner · 08-22-2012, 05:19 PM

The alt doesn't put out ac!

z28camaro94 · 08-22-2012, 05:49 PM

Then y is my multimeter showing a voltage

And yes it was on ac voltage not dc

The_Bishop · 08-22-2012, 06:55 PM

You should have roughly 13-14 volts DC at the battery when the car is running. DC, not AC.

sweetbmxrider · 08-22-2012, 07:05 PM

http://www.pvv.org/~syljua/merc/TooSeptST07.pdf

z28camaro94 · 08-22-2012, 07:46 PM

Bishop..yes I understand that and I am getting 14vdc, I was wondering y it was producing ac as well.

Bmx..thanx that should help and I could have been possibly measruing it incorrectly. Ur link says that a dmm isnt the best thing to test with...unfortunatly I cant get ahold of a oscilicope.

Def explains alot...y everything happened as it did, y I possibly cant read my comp and such. Thanks alot for the help guys. Ill post more when I find out more

NastyEllEssWon · 08-25-2012, 01:36 AM

Quote:

Originally Posted by Featherburner

The alt doesn't put out ac!

sure it does.

z28camaro94 · 08-28-2012, 07:52 AM

i had my alt tested last week and rebuilt. it tested out ok when i took it to one of my shops. but had him rebuild it neway. best 10 bucks i spent. havent put it back in yet. still wana get my new comp flashed and drop the valve body to see if a check ball got forced up into the seperator plate. will update soon

z28camaro94 · 09-06-2012, 01:26 PM

put the rebuilt alt in and got the new comp flashed and put in. still cant read it. ive been told to look for a couple of things. first, someone told me there ming be a fuse or diode INLINE with the DLC and the pins on the comp. can anyone verify this? Also that newer scanners look for a 12v signal at the connector to start to diag. but the obd1 connector only puts out a 5v signal. can anyone verify that? i have already verified that 5v is coming to the connector. I have yet to drop the valve body, but ill come to that...if anyone can shed some light on my others probs i would appreciate it

z28camaro94 · 09-06-2012, 01:33 PM

Quote:

Originally Posted by z28camaro94

put the rebuilt alt in and got the new comp flashed and put in. still cant read it. ive been told to look for a couple of things. first, someone told me there ming be a fuse or diode INLINE with the DLC and the pins on the comp. can anyone verify this? Also that newer scanners look for a 12v signal at the connector to start to diag. but the obd1 connector only puts out a 5v signal. can anyone verify that? i have already verified that 5v is coming to the connector. I have yet to drop the valve body, but ill come to that...if anyone can shed some light on my others probs i would appreciate it

i had another thread on the problem with my comp b4. i have gone through every wire and ground. verified continuity, power and ground at the connector. which is y i put in a new comp, thinking it was something internal in the comp. just so no one repeats themselves from b4

SRGN · 09-06-2012, 08:05 PM

Should be 12V on pin 16 of the DLC.

grazi · 09-06-2012, 08:20 PM

This thread has been jumping all over the place and I'm not sure whats going on here but are you trying to read the codes on your 94 with an OBD2 scanner? Prettty sure You would need a special reader to do that if so.

z28camaro94 · 09-07-2012, 08:23 AM

sorry bout being all over the place.

to make things clear, it started out i couldnt read the comp. tried many specific OBD1 scanners, without luck. Checked wires and everything. I let that prob go for a couple months cuz i have no drivability issues. then as posted in the original post the car did something wierd. so i took the steps mentioned above to try and go through everything i think it could be. did the alt first so i didnt fry my new comp. did the comp. tried scanning it, still without luck. still wanna check the tranny, but im not driving it so it can wait.

I just really want to be able to read the damn comp. SRGN- i have the a,b,m and g terminals in my connector. its the 12 pin OBD1. G being the keyless entry. am i still supposted to have 12v coming to the B terminal for the OBD1?

LTb1ow · 09-07-2012, 08:41 AM

You read from the M pin and use the ground pin. Any OBD1 12pin scanner should work, but the chances of finding one are slim, you need a professional version.

So, either buy a cable and hope it works, or accept that you may have a bad connection in your serial data line.

z28camaro94 · 09-09-2012, 09:20 AM

How can I have a bad connection at the serial data line when its continuity checks out perfect? Im not gonna just accept it, thats idiotic. I thought the scanner look for a voltage at the B terminal to start reading through the M terminal

LTb1ow · 09-09-2012, 09:35 AM

I am kinda speaking from a 95 OBD1.5 area, not 100% on the early stuff, but I know for mine, the data port serial line ties into the brake system for some weird ass reason. So what I mean was you could have continuity to from PCM to ADL port, but if the line that ties into it is fubar'd, could be throwing weird stuff into the mix.

You checked continuity from pin to pin right? Maybe theres an issue with the pin to PCM connection?

Edit: and yes, sorry B is a mode select for the scanner. A is your primary ground.

The PCM has the serial data on Blue 30 (D30). This needs to go to "M", "E", or 09, depending on your connector above. It's a tan wire on a 1994 PCM.

Mode select needs to go to Blue 20 (D20). It's a White/Black wire a my 1994.

ALDL Ground needs to be tied in to Blue 1 (D1). This ground wire actually winds its way through the chassis to get to the PCM, but it wouldn't hurt to run a jumper wire directly to it. The better your ground, the better your ALDL communications reliability.

Mode select typically isn't used on our cars for the laptop based scan tools or the LT1_Edit program. It's for diagnostic modes that only the Tech2 will allow. So, it's good to wire up if you think one day you'll hit it with a Tech2, but you don't have to have it wired up.

Last part paraphrased from AKM.

z28camaro94 · 09-11-2012, 07:21 AM

ok. thats helps.

Im gonna have to look at a wiring diagram for that serial data, see where it branches off and go from there. Im pretty sure the PIN to COMP connection is good. I dont see any visible corrosion or anything. all the tabs are locked and have the red locking clips still on them. Ill make a jumper just to see if that helps. I hate tracing wires, but I dont fix this, I wont be able to tune and whatnot.

Case of beer and tunes to anyone who wants to help for a day....haha not that anyone would