Car won't rev
Thread Starter
Racer
Joined: Sep 2002
Posts: 407
Likes: 0
From: Alma AR
Car won't rev
I need some help with my 1990 L98 coupe. I took the car out driving today and after about 30 minutes the car wouldn't accelerate at other than a very slow rate. I could just touch the gas pedal and slowly build up speed, I could maintain that speed once there, but every car on the highway can out accererate me. Also, if I did put my foot into it it would just sit ther doing nothing. If I slowly brought my foot back to a lower rate the car would pick up speed. Ther aren't any unusual noises that I can hear, just no performance. I thjink it's a fuel delivery problem, or a timing problem. If anyone can help me I'd appreciate it. 
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
it is bogging, then?
I mean, what you are describing sounds like a couple of things:
1) transmission problem, floor it all you want, and all it does is rev.
2) fuel pressure - the pump is failing, or, there is a leak.
3) throttle position sensor, but I would expect a code.
That begs the question, are there any codes? Did the SES light come on?
I mean, what you are describing sounds like a couple of things:
1) transmission problem, floor it all you want, and all it does is rev.
2) fuel pressure - the pump is failing, or, there is a leak.
3) throttle position sensor, but I would expect a code.
That begs the question, are there any codes? Did the SES light come on?
Thread Starter
Racer
Joined: Sep 2002
Posts: 407
Likes: 0
From: Alma AR
I don't think it's a transmission problem, but I'm really not sure. How could I tell? I know I can't get the car to kick down to a lower gear when I want to pass. In park it seems to rev all the way to red line. This is, by the way, the first time I used the car in about a month. When I first started the car I got a "SYS" display on the speedometer screen. But I haven't seen it since. I manually went shifted through the gears and the transmission seemed OK, but again this is the first time I did that. The engine though seemed to be a little hesitant.
Last edited by PBnf; Aug 1, 2004 at 07:30 PM.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
First, pull the code(s) and address it (them). If that doesn't solve the problem, do a fuel pressure test. It takes a lot less fuel to rev in neutral, than to pull the weight of the car. How long since you changed the fuel filter? A clogged filter shortens the pump life.
RACE ON!!!
RACE ON!!!
Safety Car
Joined: Apr 1999
Posts: 4,623
Likes: 2
From: Ohio
Originally Posted by PBnf
Other than getting the codes, is there a fast way to check tha MAP senser?
Don't be intimidated to check for codes. Nothing could be easier! It's certainly a lot more expedient than you trying to find out what the proper voltage is for the MAP, pulling the sensor, getting out the volt meter and testing it individually. $5 says it's either a fuel filter or a clogged cat. If you don't know when the filter was last changed, do it! Start with the most cost effective options first.
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Instructor
Joined: Jun 2003
Posts: 238
Likes: 0
From: Woodstock Ga
I have a 90 L98 as well and one afternoon coming home from work i had the same problem. I was getting an ocasional SYS flashing on the dash and the car just would not accelerate. It wouldnt bog but it would just not go... When i got home and pulled the codes i got code 55 ecm problem.... but the funny thing was i never got a Check Engine light just the SYS flashing occasionally. So off to autozone i went picked up an ECM and voila problem solved. So in my case i think i was experiencing what the GM engineers called "Limp Home Mode" which is hard coded into the memcal (chip)
Thread Starter
Racer
Joined: Sep 2002
Posts: 407
Likes: 0
From: Alma AR
It seems like pulling the codes is the thing to do. Now I don't have a volt meter or anything else that can access the terminal under the dash. How can I get those codes? What's the procedure? Thanks.
Le Mans Master
Joined: Jul 2002
Posts: 5,818
Likes: 2
From: Alive and well in Burlington NC
Here's a link to some good info and the procedue to pull your codes:
http://www.c4vettes.com/codes.htm
http://www.c4vettes.com/codes.htm
Drifting
Joined: Nov 2002
Posts: 1,593
Likes: 0
From: Mobile AL
St. Jude Donor '05
Yeah, I'd have bet on MAF exept it will almost always throw a code. If there's no code and runs like crap, it's probably ECM that does not have enough brains left to tell you it's sick. Thus the "limp home" mode.
Melting Slicks
Joined: Mar 2002
Posts: 3,252
Likes: 6
From: The Colony Tx
I had a similar problem in my 88 and it turned out to be the cat. If you don't get any codes, an easy way to check this is to drill a small hole just behind the converter and see if you are getting exhaust out of the hole. Or, just take it to a muffler shop. They symptoms I had were that the car would not rev over 3500 RPM and it sounded like the tranny was slipping at that RPM.
