94 Firebird - Loss of power in D


Old 04-19-07, 10:37 PM
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94 Firebird - Loss of power in D

I have a 94 Firebird that at first I was thinking it was the EGR Valve, I replaced it and the check engine light now does not show. (I was getting Error code 75, 76, 77).

I thought that would be the fix all to my problem, although I still have this situation.

In Reverse the car is fine. When I place the car in (D) it acts like it is in 4th gear, I have to manually place the car is (1) or (2) and then shift up into (3) or (D).

I was thinking that it was the linkage cable. I am not sure... Is there possibly a different problem?

If it is the linkage cable what is the best way to adjust this, or should I have a professional do it?

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Old 04-20-07, 05:50 AM
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Sounds Like Your Tranny Isn't Downshifting
Old 04-20-07, 07:25 AM
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I thought 75 on OBD-1 GM's was low voltage, but I surfed and found a chart that does refer to EGR.

75 Digital EGR #1 Solenoid Error
76 Digital EGR #2 Solenoid Error
77 Digital EGR #3 Solenoid Error

Just for grins, I think I would check alternator output for proper voltage regardless of the codes. Often tranny problems are misdiagnosed because of low voltages that the computers don't like.

You can also reset your codes by disconnecting the battery; then you can see if they, or any new ones, reappear.
Old 04-20-07, 11:49 AM
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The tranny is downshifting while I am driving on the highway with no problem. It is just on take off.

Thank you
Old 04-20-07, 05:06 PM
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I can tell you from experience that a low voltage on some GM's (like the 4L80E in my wrecker) will cause the computer to default to a mode where you don't have all the gears.
Old 04-20-07, 06:20 PM
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I did a simple test on the Alternator, there is a little concern there, although I have been driving short distances for 2 days now. The battery is still fully charged. I am starting to think along these lines:

Wheel Sensor
Speed Sensor
MAP Sensor
Oxygen Sensor

There are so many sensors that would cause this. I have determined that I have missed a symptom.

Driving Tests
Start Up: Car starts and idles great approx. 900 rpms, engine slightly rough
Reverse: Squeel Tires with full accelerator, full power
From 0 - 10mph (D): No power, full accelerator, 25 - 30 seconds
From 0 - 10mph (3): More power, full accelerator, 5 - 10 seconds
From 0 - 10mph (2): More power, accelerator, 2 - 3 seconds
From 20 - 30mph (D): Normal shifting, driving, car is engine shaking
From 40 - 60mph (D): Normal shifting, driving, car is engine shaking
From 60 - 80mph (D): Normal shifting, driving, car is smooth no shaking
At idle after driving (1), (2), (3), (D): Car is engine shaking rough
At idle after driving (N): Very smooth - No shaking

Alternator test:
idle @ 900rpm with lights on 13.6V
idle @ 900rpm with lights and AC 13.5V
idle @ 900rpm 13.7V
1500rpm with lights on 13.8V
1500rpm with lights and AC 13.7V
1500rpm 13.9V
Old 04-21-07, 03:48 PM
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Ok here is the latest:

Well at this point, I did find a hose off of the MAP Sensor, by replacing the hose, the car is extremely smooth on idle, it sounds like it is ready for the mile. I thought that would do it, the car is sounding great. I jump in, throw it in reverse and squeeled the tires out of the drive way (before I had to almost floor it to get it out of the garage). The smile came across my face, I throw it into Drive clinch the steering wheel, brace my self into the seat, and slammed the accelerator to the floor, a kid on a big wheel passed me in the first 200 feet.

I gave up, to the shop I go. After about 3 hours at our local Pepboys (The only thing that was open on Saturday) He came back with this:

3, 5 and 6 cyl. no compression

1 = 110psi
2 = 115psi
3 = 80psi
4 = 122psi
5 = 55psi
6 = 70psi

He basically told me to go buy a LS2 and install it in the car. I paid the 92.00 for the diag fee and was thinking to myself as I was leaving. Why can I squeel my tires in reverse, get up to about 120MPH on the highway and this car when at idle now is running smooth.

Can anyone enlighten me on this subject. Could it be the computer? I am at a total yaw at this. I am going to a transmission shop on Monday to see what they say. I would love to have the LS2 with 6 speed Man Trans. but the $5599.99 price tag plus the labor to install it, is just a little out of my budget. (about 5599.99 + labor out of my budget )

I can not believe I need to scrap this engine.

Any thoughts would be great.
Old 04-21-07, 04:50 PM
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Assuming they were adept at doing the compression test, you've got some serious compression problems. I'm a little skeptical, too, that with those readings you otherwise are running pretty well except for the bad acceleration. I think the tranny shop visit is a good idea; I'm thinking maybe something like bad shift solenoid(s) or other electronic problem related to tranny operation. You have a good, solid tranny shop to go to, I hope?
Old 04-22-07, 04:53 AM
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Cool low compression

First of all, I notice low compression on cylinders 3,5 and 6, not no compression. Plus, the mechanic should had done a wet compression test as well, where you shoot in a few drops or motor oil to seal any worn piston rings and see whether the pressure rises indicating worn piston rings. On the other hand I would not consider it a head gasket since from what I found is the cylinders are on opposite sides of the engine. As shown here, http://www.edelbrock.com/automotive_new/misc/tech_center/install/2000/2114.pdf or here http://img.photobucket.com/albums/v729/matthewmetallo/V6001.jpg and here http://img.photobucket.com/albums/v729/matthewmetallo/V6002.jpg
Now, loose spark plugs could be to blame or valves that are not seating due to crub buildup. I dont recall what if the camshaft lobes were wiped out on those cylinders would effect compression, maybe someone could help with that question. I couldn't find a V6 pontiac diagram so I just used a Chevy V6, to get an idea of where the cylinders were located.
Although, you could have a blown head-gasket between 3 and 5 and something different on 6, such as a leaking valve. I would redo the compression test with a few drops of motor oil, first!

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