Help! Fuel issue: At least I think it may be but I dont know what else to do?

[HuskerNation]

Hello,

I have an 89 Coupe 6 spd, I drive about 6-12 times a year and while this year I have driven it quite a bit more. The vette is all stock with 71k miles & have owned my vette for over 10 years. Recently had an issue where it is dying, cutting out, rpm dropping, rough idle and when racing up engine too, at start up idle fluxuates between 300-1200rpm without touching the gas pedel. Once in a while it seems to be running fine but is way down on power. I also tried the a-b jump wire and only got the 12-12 handshake code. Also never have I gotten a check engine light to come on, at any time.

Actions I took: replaced the fuel filter, fuel pump and ignition coil. no effect by doing these.

One odd factor: when I initially had this problem I was on a drive and managed to get it home. Once in the driveway I was racing the engine up thinking something had to just get "blown out". I immediately pulled the vette in the garage & turned it off. When I opened the hood it looked like I was getting a little bit of smoke, almost steam like coming from somewhere around the distributor. I cannot find anything burnt, melted or the like, nor could I pinpoint a source then or now. I dont know if this has anything to do with the problem but I wanted to mention it anyway.

Finally, as much as I would like to be, i am not a mechanic. I try and often succeed, but electrical and fuel truely baffle me. Where to go from here, how to do things......I really need guideance and help.
Thank you, Brian

 

[gmjunkie]

Hello,

I have an 89 Coupe 6 spd, I drive about 6-12 times a year and while this year I have driven it quite a bit more. The vette is all stock with 71k miles & have owned my vette for over 10 years. Recently had an issue where it is dying, cutting out, rpm dropping, rough idle and when racing up engine too, at start up idle fluxuates between 300-1200rpm without touching the gas pedel. Once in a while it seems to be running fine but is way down on power. I also tried the a-b jump wire and only got the 12-12 handshake code. Also never have I gotten a check engine light to come on, at any time.

Actions I took: replaced the fuel filter, fuel pump and ignition coil. no effect by doing these.

One odd factor: when I initially had this problem I was on a drive and managed to get it home. Once in the driveway I was racing the engine up thinking something had to just get "blown out". I immediately pulled the vette in the garage & turned it off. When I opened the hood it looked like I was getting a little bit of smoke, almost steam like coming from somewhere around the distributor. I cannot find anything burnt, melted or the like, nor could I pinpoint a source then or now. I dont know if this has anything to do with the problem but I wanted to mention it anyway.

Finally, as much as I would like to be, i am not a mechanic. I try and often succeed, but electrical and fuel truely baffle me. Where to go from here, how to do things......I really need guideance and help.
Thank you, Brian

A bad ignition module will act that way!

 

[HuskerNation]

That sounds like a good place to start. What suggestions do you or others have as to performance upgrades to the ignition on the currently stock vette engine? I was using an MSD coil but had problems with the tach reading correctly. Should I use the MSD again and if so what does one have to do to get the tach to read right?

 

[John Robinson]

Why not use what GM designed for the car. They made millions of engines with distributors and they worked for day to to day driving. Maybe if you were going to convert the car to a pure race car you would look for something else. Despite what the adds say nobody has more knowledge than GM. A speciality after market manufacturer can probable make something that will work but remember it is focused to improve some aspect of the cars performance. That usally comes as a trade off for not doing something else as well. Lately I have been reading that the MSD replacement for the opti LT1 engine is causing issues with not running well. If you have the original distributor try to put it back in and see how it runs. Many years ago I learned not to trust the replacement parts as being good. I had a car that I changed the wires the coil, the plugs, the points etc. The car would not run over 50 MPH after that. After 8 hours using a sun machine and everything else I could think of I put the old coil back on the car and it ran fine. So much for the old saying that a coil either works or it does'nt. That was a case were the coil worked just good enough to make me know it could not be bad.

 

[HuskerNation]

Point well taken John. Yes, for now I plan on using standard replacement parts since I am having a driveability issue. That way I can at least figure it out & get it back going down the road again.

It is frustrating sometimes how you think your improving things with an aftermarket item and then it adversely affect the vehicle. It truely makes one understand how things need to "work together"!

 

[steveb01z06]

Checking for a vacuum leak wouldn't require any investment in expensive parts. If that checks out, spark plug wires are known to go bad with less mileage than you have.

 

[HuskerNation]

Just installed a new ignition module, no difference she is still dying on me & running bad. I did the jump a-b wire and still no codes thrown.

Any suggestions as to the next area or how to diagnose from here?

 

[HuskerNation]

I hate to admit it again, but being a backyard mechanic I have no idea how to check for a vacuum leak. However the vette was given a complete tune up in the last 4-5k miles which included plugs, wires, cap, rotor.

I am starting to wonder if its a fuel pressure issue? If so where do I start checking & how?

 

[boomdriver]

yeah....

you;re wasting your time trying to diagnose an EFI engine without the very basics...

Fuel, pressure and injection

spark, base timing, knock sensor, ESC and dist module


FSM. The Bible for a Corvette. $100 investment will save a thousand in the 1st year.

Fuel pressure test gauge.
Spark tester.
Noid lite.
DVM
FSM

Get those and you'll know whats wrong with it in 10 minutes.

From what you describe, its low fuel pressure. Burping, backfiring and stumble IS fuel pressure. Takes 40 psi to run right.
<30 and it dies.
Takes a pump that can keep up the demand.
Injectors also go south and cause these problems. Use the DVM to ohms test each inj. 16ohms is good,
less than 12 is suspect. That only confirms the inj ability to cycle, not how well it sprays. Thats a given...poorly. But, as long as the pressure is up they should run the engine ok. Get some 20th century injectors eventually from FIC...the stock inj are crap to start with.

Your options...low fuel pressure. You said you changed the filter? which filter?
Low voltage. But that has to be real low...like 11V and dropping to act like this.
Go with fuel pressure and/or regulator. Bad regulators act like shorted injectors. Pull the vac line off the reg to see if its got gas inside,. if so replace the reg. Check the oil for gas..if so, replace the reg and the inj.

The smoke from behind the dist is the intake gasket oil leak OR the oil sender leaking down onto the exhaust. Look into that soon...

 

[HuskerNation]

Thank you for your insight & direction. I went & picked up a fuel Pressure gauge , DVM, found my old hayes manual too.

I was also looking at an Actron cp9185 elite scanner, its said to do both obd 1&2. Is it a good scanner to buy?

Also, I had no fuel pressure on the guage when I tested the vette?? I will just have to try again tomorrow.

Btw, fuel filter replaced with fuel pump.

 

[Schrade]

It is frustrating sometimes how you think your improving things with an aftermarket item and then it adversely affect the ???.

That's what they do in Washington DC. If it ain't broken, fix it til it is.

And if it IS broken, don't fix the problem, but give money to Advance / Zone, and let them roll the dice with your wallet..




Stay basic; if no DTC, then check air, fuel, fire.

Air filter clear? Vacuum leaks (DWELL ON THAT LATER).
Fuel; Static and dynamic fuel pressure ok? Just getting gas in the hole don't get it any more...
Fire. Plugs good? Wires good? WIRES ROUTED PROPERLY??? Hi-energy discharge from mis-routed wires lights up EMI same as a nuke = false codes, etc.

 

[HuskerNation]

Played around with a fuel pressure guage. the first couple times I tested it I got no pressure at all. Either at key on, or after at as I ran the engine. (She still ran the same, hard to start but would then die shortly after.) Since it was a loaner I bought my own and tonight only hooked up the line of my fuel pressure guage to my shrader valve. The other end went into a empty container to catch gas at key up.

The first time I turned on the key I could hear the pump working and my assistant (wife) said gas was going into the container. So, I turned key off, & tried again, but only clicking at pump not the 2 second run it should have. I tried it a few more times, and even pulled the key from the ignition out as well, but at no time did I hear the pump run. In addition no gas was coming out into the container either!

As you may recall, I had replaced the fuel filter and fuel pump with a new sock on the pump as well once this issue started. My old fuel filter was not plugged and at this point I dont think the lines are either. I am thinking its a bad new pump or could it be something else? A fuel pressure regulator, a sensor, or something else????

Also, no leaks of fuel anywhere, no loose fittings either. The fuel pump was a stock replacement from Autozone, an Airtech, I believe.

 

[John Robinson]

I don't see any were that you have checked the fuses. I don't know on your 89 but on my 93 I have two fuses labeled eng 1 and eng 2.

 

[LT4man]

I have used Actron scanners. They have performed well. The one you are looking at would be fine for your vehicle & also any OBDII vehicles. Be sure to get the optional OBDI cable.

When you hook up the fuel pressure gauge, I would not direct any fuel into a container. Just hook up the pressure hose to your schrader valve. Cap off any other hoses on the gauge.

I am always wary of having any gasoline exposed to the engine compartment.

 

[Schrade]

Played around with a fuel pressure guage. the first couple times I tested it I got no pressure at all. Either at key on, or after at as I ran the engine. (She still ran the same, hard to start but would then die shortly after.) Since it was a loaner I bought my own and tonight only hooked up the line of my fuel pressure guage to my shrader valve. The other end went into a empty container to catch gas at key up. .

Catch gas? The FP guage usually doesn't have an outlet. It's like a tire guage. (unless there's a pressure let-off that has to be closed... .

The first time I turned on the key I could hear the pump working and my assistant (wife) said gas was going into the container. So, I turned key off, & tried again, but only clicking at pump not the 2 second run it should have. I tried it a few more times, and even pulled the key from the ignition out as well, but at no time did I hear the pump run. In addition no gas was coming out into the container either!.

I think ECM waits for 8 minutes to reset. Remember VATS failures? It reset after 8 minutes (or so)...

As you may recall, I had replaced the fuel filter and fuel pump with a new sock on the pump as well once this issue started. My old fuel filter was not plugged and at this point I dont think the lines are either. I am thinking its a bad new pump or could it be something else? A fuel pressure regulator, a sensor, or something else????.

You have to get a reading FIRST, along with pressure bleed-down time. PERIOD. .

Also, no leaks of fuel anywhere, no loose fittings either. The fuel pump was a stock replacement from Autozone, an Airtech, I believe.

Leaks, if present, are at the weak link - injectors, fuel pressure regulator. STATIC FP TEST FIRST.

 

[John Robinson]

The question is can the new fuel pump be bad. The answear is yes. Take a look at the new fuel pump I put in and then had to replace within a week. Notice the pin hole in the pump.

 

[Schrade]

I don't see any were that you have checked the fuses. I don't know on your 89 but on my 93 I have two fuses labeled eng 1 and eng 2.

I think if he had fuel flowing once, when he had the guage on, didn't that confirm fuse good?

I think fuse slot #2 is reserved for LT5, with secondary fuel pump...

 

[John Robinson]

Another question for the OP. How old is the gas? When not being driven do you just pull it into the garage or does it sit outside? Bad gas will make the car run really bad. Two things happen when cars are stored for long periods. One the gas evaporates and what is left does not have the flash point for good combustion. Second the inside of the tank becomes a small invironment of it's own. Over time it will make water from the humidity in the air.

 

[John Robinson]

I think if he had fuel flowing once, when he had the guage on, didn't that confirm fuse good?

I think fuse slot #2 is reserved for LT5, with secondary fuel pump...

That only proves the fuse was good that time. The purpose of the fuse is to protect the wiring and the thing it is attached to . If there was a short or a crossed wire the next time he turned the key the fuse would blow. Which takes us back to determining if the pump is defective. And if the fuse were blown it certainly would then give a direction to start looking for what caused it to blow.

You are correct about fuse slot two. I believe there is a 30 amp fuel pump fuse in the fuse block by the battery. Or it may be a fusesible link.

 

[HuskerNation]

Ok, So I finally got a chance to mess with the vette today and here is what I have found out. Fuel pressure relay looks to be good as a new one made no effect. All fuses are fine, gas is less than 2 weeks old.

While I was checking and trying things I noticed that when I turned on the ignition key and listened to the pump activating, my fuel pressure would show 3 lbs. After it started it was showing around 60 lbs at an idle or rough idle. Therefore I pulled the connection off the oil pressure switch behind the distributor on the drivers side and started it. Oil pressure read 80 lbs but she seemed to run completely normal!

I am going to try this again and if it truely is running fine then go and replace the oil pressure switch and drive it a little bit. I will let you all know the final outcome soon.