white/blackss

ok so i have a 1994 z28 auto and since i got this thing the ses light has been on and the car runs in limp home mode.

i receantly put the 1997 dash and interior wiring harness in the car but the light is still on. i tried to pull codes but it says, no communication with computer.

i just bought a used but good ecm from a 1994 firebird auto that didnt have the ses light on and put it in my car and that dang light is still on.

i`ve also replaced the following,

m.a.f.

m.a.p.

e.c.m.

wires

plugs

cleaned and replaced all ground wires everywhere, the car is hard to start when warm and smokes black for a second upon start up when warm.

also it kinda surges and i notice that i have to push the accelerator pedal down farther to get moving when its warm.

does this sound crazy or what?

please help if you can im going crazy over here with this thing.

Dave '97 Z28 M6

If you've got a '94 car & computer (OBD1), and a '97 dash and wiring harness (OBD2), could that cause the problem of no communication with the computer? Maybe someone with more knowledge than me will chime in.

shoebox

You are going all about this the wrong way. You need to resolve your communication problem and see what the SES is about. Throwing parts at it is a big waste of money and time. Any time you do rewiring or transplanting, you need to know exactly what you are getting into.

95z28pwr

Same thing with mine. SES light, usually after engine warmed and fan came on. Hard starting as well. Had fuel system diagnosed for starting problem, needed to replace pump and regulator and SES light gone.

white/blackss

Can I Just Match Up The Wire Colors On My 12 Pin Aldl To The Wiring Harness From The 16 Pin?

All The Wires Are The Same Accept The Purple, Orange, And The 1997 Harness Has 2 Black With White Trace.

Im Gonna Try That And See If I Can Scan It That Way.

Also, Does Someone Here Have The Actual Wiring Colors At The Aldl So I Can Match Them Up, And So I Can Trace Them To The Pcm And See If Maybee I Can Scan It At The Pcm And See If I Get Communication That Way?

Shoebox, Any Ideas?

This Is Starting To Become A Real Big Pain In The ***.

Well Thanks In Advanced For Any Help.

Injuneer

What are you using to try and pull the codes? If I read this correctly, you installed the 97 dash INCLUDING the 16-pin connector? Correct? If so, what are you pluggin into it, since you need an OBD-I scanner, and they will only attach to a 12-pin connector (unless you have the adapter cable/plug for a 95).

How do you know its in "limp home" mode? That only happens when the PCM has lost almost everything it needs to keep the engine running. Some faults that turn on the SES light do not invoke any changes to the control system, and many make simple substitutions using data from other sensors, or preprogrammed tables. "Limp mode" is a defined operating modes that few PCM's ever experience.

Appears you didn't try to scan it at all before you changed the dash.... 1st mistake. Then you swapped the dash without knowing the impact on the ALDL connector. Another mistake. Then you started spending a small fortune on new parts, without knowing the old ones were bad....... what's wrong with this picture?

Shoebox has the ALDL connector pinouts on his Tech Pages. He also has the wiring diagrams for the 1995 PCM, and it will be identical to your 1994 as far as the wire colors. The pinouts will be different, since he has the oddball 16-pin connector with the

white/blackss

its in limp mode, the fans run all the time and the car only gets 6mpg.

as far as the parts i bought them from auto zone and returned them when they didnt solve the problem.

also i did scan the car before i swapped the dash out and i got the same thing, " unable to communicate with computer "

and as far as the aldl i removed the 16 pin and matched up the 12 pin to the wiring colors. i still have to try and scan it today and see if i can get some codes.

im using a 2005 model snap on solus scanner, this should be able to scan this car as it scans my co employee`s 1996 lt1 with no problems and we used it with a 1994 caprice police car with the same lt1 as mine and it scanned that fine too.

i`ll post back in a few minutes to let you all know if i can read the codes or not.

white/blackss

well finally got the codes and they were for the ect, maf , and air temp sensor, i changed them and the lightwent off.

the reason i couldnt scan the car was because the data serial wire has a break from the pcm to the aldl, i ran a wire from the pcm to the aldl and sure enough it pulled up all the codes, thanks for all your help on this, i needed it.

b.t.w. what temp should this car be running at? the fans come on around 215,
is that right?

Dave '97 Z28 M6

That's normal. Many guys get their PCM's re-programmed to turn them on sooner. Others (like me) run a manual switch. Most of us just don't like seeing the engine get that warm.

Injuneer

No... 1st fan (or low speed in later models) comes on at 226degF, the 2nd fan (or high speed) at 235degF. - stock programming.

You need to read the temp off the PCM, since it uses a different sensor than the dash gauge.

RICEFEDZ28

What Scanner Are You Using To Pull Codes? I'm A Mechanic In Sterling Heights With Access To A Good Scanner.

Dave '97 Z28 M6

Sorry I don't know why I thought 215 was the turn-on temp. Must've had a brain-fart or messed up the *C -> *F conversion.

Good to know about the different sensors, too.