Weird starting problem and back-firing
Thread Starter
Intermediate
Joined: May 2013
Posts: 27
Likes: 0
From: Cincinnati Ohio
Weird starting problem and back-firing--Please HELP this is my DD.
Hello,
I have a 85 corvette with automatic transmission. The problem started last Friday, when my car would crank and then die. Sometimes it would start, go rough for a few seconds and then die. I checked the fuel pressure and found it low. I changed the fuel pump. That problem SEEMS to have gone. My second problem occurred after I changed the fuel pump. And this is what happens:
After putting in the key and cranking it, the car goes rough and keeps on going until I keep pressing the gas pedal. While I am pressing the gas pedal, the jumps sometimes and also backfires sometimes.
So, I checked the MAFS (it seems fine, all three platinum wires intact) and cleaned it with Brake Fluid Cleaner. The car still gave me the same problem. So, I unhooked the MAFS and still the same problem.
Please help as this is my DD.
I have a 85 corvette with automatic transmission. The problem started last Friday, when my car would crank and then die. Sometimes it would start, go rough for a few seconds and then die. I checked the fuel pressure and found it low. I changed the fuel pump. That problem SEEMS to have gone. My second problem occurred after I changed the fuel pump. And this is what happens:
After putting in the key and cranking it, the car goes rough and keeps on going until I keep pressing the gas pedal. While I am pressing the gas pedal, the jumps sometimes and also backfires sometimes.
So, I checked the MAFS (it seems fine, all three platinum wires intact) and cleaned it with Brake Fluid Cleaner. The car still gave me the same problem. So, I unhooked the MAFS and still the same problem.
Please help as this is my DD.
Last edited by aks8586; Jun 4, 2013 at 11:22 PM. Reason: Formatting.
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
There are a few more major parts in the fuel line to check. The filter, the Fuel pressure regulator, and the injectors. A bad FPR can cause these very symptoms, though I am not very well versed on the L98.
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
Not sure about the L98, but possibly just pull them and check for leaking? Also check voltage to see if they're firing.
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
Hello,
I have a 85 corvette with automatic transmission. The problem started last Friday, when my car would crank and then die. Sometimes it would start, go rough for a few seconds and then die. I checked the fuel pressure and found it low. I changed the fuel pump. That problem SEEMS to have gone. My second problem occurred after I changed the fuel pump. And this is what happens:
After putting in the key and cranking it, the car goes rough and keeps on going until I keep pressing the gas pedal. While I am pressing the gas pedal, the jumps sometimes and also backfires sometimes.
So, I checked the MAFS (it seems fine, all three platinum wires intact) and cleaned it with Brake Fluid Cleaner. The car still gave me the same problem. So, I unhooked the MAFS and still the same problem.
Please help as this is my DD.
I have a 85 corvette with automatic transmission. The problem started last Friday, when my car would crank and then die. Sometimes it would start, go rough for a few seconds and then die. I checked the fuel pressure and found it low. I changed the fuel pump. That problem SEEMS to have gone. My second problem occurred after I changed the fuel pump. And this is what happens:
After putting in the key and cranking it, the car goes rough and keeps on going until I keep pressing the gas pedal. While I am pressing the gas pedal, the jumps sometimes and also backfires sometimes.
So, I checked the MAFS (it seems fine, all three platinum wires intact) and cleaned it with Brake Fluid Cleaner. The car still gave me the same problem. So, I unhooked the MAFS and still the same problem.
Please help as this is my DD.
They do sell a "MAF Cleaner" spray...brake clean is a little too harsh + it eats plastic on contact if you didn't know already.
have you checked for stored trouble codes yet?
the '85 has a year specific MAF circuit/module that has proven to be a little more problematic and difficult to troubleshoot than the years that followed.
To me - from what you've described - your issue does sound like a MAF related issue....might check/clean the simple stuff like the MAF main connector's & wire pins/contact points.
Thread Starter
Intermediate
Joined: May 2013
Posts: 27
Likes: 0
From: Cincinnati Ohio
Thanks guys for all the help.
This is my first American and first muscle car. My knowledge about Corvette is zero. I can work on my fiance's camry and the celica I had, but Corvette seems kinda "mysterious" to me. So, I took it to a shop today and will know what is the issue with the car by tomorrow.
I planning to be there when they look at the car, so I can learn a thing or two.
@engle1147: I know about the MAF spray; does it really work though? I always thought that MAF spray was a marketing scam. Also, I checked the MAFS today, its good. Not really an eletrical person, so did not check the relays and the fuses.
@lt4obsesses: Thanks; however, I got frustrated and took it to the shop.
This is my first American and first muscle car. My knowledge about Corvette is zero. I can work on my fiance's camry and the celica I had, but Corvette seems kinda "mysterious" to me. So, I took it to a shop today and will know what is the issue with the car by tomorrow.
I planning to be there when they look at the car, so I can learn a thing or two.
@engle1147: I know about the MAF spray; does it really work though? I always thought that MAF spray was a marketing scam. Also, I checked the MAFS today, its good. Not really an eletrical person, so did not check the relays and the fuses.
@lt4obsesses: Thanks; however, I got frustrated and took it to the shop.
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
Thanks guys for all the help.
This is my first American and first muscle car. My knowledge about Corvette is zero. I can work on my fiance's camry and the celica I had, but Corvette seems kinda "mysterious" to me. So, I took it to a shop today and will know what is the issue with the car by tomorrow.
I planning to be there when they look at the car, so I can learn a thing or two.
@engle1147: I know about the MAF spray; does it really work though? I always thought that MAF spray was a marketing scam. Also, I checked the MAFS today, its good. Not really an eletrical person, so did not check the relays and the fuses.
@lt4obsesses: Thanks; however, I got frustrated and took it to the shop.
This is my first American and first muscle car. My knowledge about Corvette is zero. I can work on my fiance's camry and the celica I had, but Corvette seems kinda "mysterious" to me. So, I took it to a shop today and will know what is the issue with the car by tomorrow.
I planning to be there when they look at the car, so I can learn a thing or two.
@engle1147: I know about the MAF spray; does it really work though? I always thought that MAF spray was a marketing scam. Also, I checked the MAFS today, its good. Not really an eletrical person, so did not check the relays and the fuses.
@lt4obsesses: Thanks; however, I got frustrated and took it to the shop.
Taking it to a shop is nothing to be ashamed of. There is a learning curve here. Now if you can learn to work on a Camry, then you will be able to learn to work on this one too, all the basic principles apply. But going to a shop at this stage is alot smarter than throwing parts at it.
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Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Make sure to do a little easy and free steps before you start replacing parts. I would suggest cleaning your throttle body and IAC valve. And the other person that suggest a Fuel Pressure Regulator is also correct, it could be that or a filter. Also pull a few spark plugs and see the condition, maybe there's oil on them, or maybe they are burnt. When you say that it backfires some times, that could be an indication of a bent valve, which also MAY be your problem. I don't want to scare you with that, but that would be the last thing I would consider. It's also possible that you have a damaged or worn valve return spring. If you want to diagnose that you can do a compression and leak down test. Top end work isn't really too much to worry about, it's bottom end that gets pricey and tedious. So try cleaning everything first and let us know what happens. Good luck to you! 
Team Owner
Joined: Sep 2003
Posts: 20,179
Likes: 673
From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
What is your definition of backfire?
Lean- "back" thru the aircleaner. Rich - "back" out the tailpipe
Pull the vacuum hose on the FPR. If you find fuel replace it.
Suggestion to all, Before you consider cleaning the MAF, go to the parts store and price a replacement.
Lean- "back" thru the aircleaner. Rich - "back" out the tailpipe
Pull the vacuum hose on the FPR. If you find fuel replace it.
Suggestion to all, Before you consider cleaning the MAF, go to the parts store and price a replacement.
Thread Starter
Intermediate
Joined: May 2013
Posts: 27
Likes: 0
From: Cincinnati Ohio
Thanks, guys for all the help.
So, as I said, I gave the car at a shop and got it back yesterday. At the shop, it was a case TMI for me-Learned a bunch of stuff, forgot a bunch of stuff.
Anyways, the car runs fine now. The mechanic said it was the ECM. What are your thoughts on this?
BTW, I have bought the service manual--Awesome stuff.
So, as I said, I gave the car at a shop and got it back yesterday. At the shop, it was a case TMI for me-Learned a bunch of stuff, forgot a bunch of stuff.
Anyways, the car runs fine now. The mechanic said it was the ECM. What are your thoughts on this?
BTW, I have bought the service manual--Awesome stuff.
Intermediate
Joined: Mar 2010
Posts: 41
Likes: 0
From: South Dakota
That sounds exactly like what my 90 was doing. My car was acting up off and on for over a year. We tried replacing a few different things and finally got to the point where we said heck with it and just replaced the ECM. It immediately ran great and I have had no issues with it since. I think you may have your problem solved!