So I bought my 1985 4+3 Corvette about 2500 miles ago. I was in the midst of a tune up because it seemed like the car would struggle to go passed 36800-3800 rpm. I figured, no problem...just some tuning up, TPS, etc and it'll be all good. Well, it kind of was until it started missing at the 3600-3800 range again.

Now, I get a bucking/surging through the gears regardless of temp. Idle is fine, off idle is fine...as soon as you start delivering engine load the car starts to cut in and out. It's losing power to the point of not being able to scale hills after it's been driven for a while. The idle begins to go lower, and the engine will run in a higher temperature range than normal...but that is to be expected with missing.

I'm suspecting fuel problem or catalytic converter problem. Anything else it could be? The problem was progressive. It does it hot or cold, but get worse after a 45min + drive.

 

Fuel problem is correct.


replace your Fuel pump and filter and report back to us

 

check the resistance at the injectors if you dont see results with the fuel pump. What is the mileage. what else have you checked/replaced so far?

 

Fuel pump, filter & strainer.

Test the theory with fuel pressure test. 40 psi at idle. ANY fluxuation on the gauge indicates plugged filter or bad pump. Always replace ALL when you go IN the tank. Always use a new tank gasket.

When your engine struggles and burps at low rpm, backfires and chokes...thats a MAF. At midrange and up, thats poor fuel flow. Your engine needs at least 30 psi to run close to right. Less than that and it burps, stumbles, coughs and embarrasses you.

Spend $75 tomorrow on a FSM so you can accurately diagnose a computer controlled engine. The money on the tune-up was a partial waste unfortunately. The FSM would have sent you to the fuel pressure right away.. These cars will eat your wallet alive if you attempt to apply old school thinking and mechanics to the C4. They are the 1st generation of complicated engine management and the old rules do not apply anymore. Takes some getting used to, but the book helps by saving you from throwing parts at problems. Expensive parts...

Get the FSM, a fuel pressure test gauge, a noid light, a cheap DVM, spark tester, a can of PB blaster, a tube of anti-seize, some silicone grease and you;re set.

And remember, these cars LIKE Delco electonics...in modules and ignition parts. The generic store brands cause as much trouble as they save money because they are not calibrated for the C4. Much of the Vette as far as parts is Noted as "Corvette Only" because the part does not fit anything else. This drives the cost UP and the best reason to have a FSM to guide you thru repairs and diagnosis. Not talking about haynes or chitlin manual either. 2 useless books if there ever were.

As the others have stated, move from filter and pump to injectors. Ohms testing is only part of that. The book will describe the rest. Typically a clogged CAT will bog and just perform sluggish...like you were driving up a steep hill until it cannot climb it anymore. That gets worse until it'll struggle to get up to 20 mph. Not so much misfiring or burping...just gutless.
If fuel system checks Ok and this gets worse with time, heat then take the dist apart and get the IGN module tested. That NEEDS to be Delco for sure. These fail from excessive heat and MUST be installed in a puddle of silicone grease. Otherwise they overheat and cause misfire.

 

So far I've replaced the fuel filter...and it was PRETTY bad. An old guy owned it and kept it sitting in a garage. It's got 92,500 on it now. It's slowly been dieing for the last couple hundred and the rev issue was when I got the car. I seriously doubt it would be an injector problem, as it had intermittent problems going higher revs and now it's just dumped all together. I'm pretty sure it's the fuel pump after looking at the filter, but the fuel pump is a cheap/good/fast fix, so I'll do it anyway.

The low range is fine, mid/high is just bad news.

I'm a younger guy, with my last car being an LT1 Trans am, the computer doesn't scare me As for a waste on a tune up, it's SOP when buying a new car for me
I figured ignition/fuel overhaul was going to be incoming anyway.

1. Min idle adjust (now it will be off, lol =P )
2. tps adjust
3. tune up
4. fuel filter
5. egr valve

I'm going to buy a Delphi pumps tomorrow and go nuts Thanks!

 

Replaced cap/rotor/coil
Replaced fuel pump/fuel filter

No good.

 

Did you install a fuel pressure gauge?

 

No, I'm running out of money and I don't see it necessary with a brand new filter and pump. But, it's still running the same, and a little jumpy at idle.. Unhooking the FPR makes it run even worse, so I'm further convinced it's loading up on fuel and it's quite possibly a MAF or other fuel metering system. I figured it wasn't the fuel pump from the start.

The car, and the wiring is too clean and in too good of shape for this craziness to be happening. I've seen and worked on too many LT1s and LS1s beat to **** and sitting outside not running for years and not suffer any problems for this to be happening to a TPI system.

Also replaced coolant temp sensor.

 

^^If you have a FPG installed and you see it drop below the minimum pressure, you know it is fuel.....

Even if you replaced those components and in your mind call it good.....there are a 1000 other things it might be concerning fuel....

The lines run right by the rear jack point, has someone in the past 27 years crimped one of your delivery lines?? You don't know....and without monitoring the fuel pressure (symptoms that are most logical for your issue) you'll never think to go beyond looking at FP Filter etc...

 

You might want to buy a cheap ohm meter and check the injectors. Harbor Freight sells one for a couple of bucks. Its not a professional model by any means but will tell you if you have a bad injector or two (or more). They should all read the same (around 16 or 17 ohms as I remember). Check them hot and cold.

 

We don't have a low fuel issue, it actually seems to be a HIGH/intermittent fuel issue. It's an intermittent jerk/power/no power/good idle/high idle/low idle.


16.9->17.1

 

check the wires coming out the back of the dist, for the insulation rubbed off, then check the icm and make sure the plugs arent loose , take a good look at your grounds, btw if it hasnt been mentioned, pull codes

 

Everything is clean, good. No codes.

 

With a new, used car, I always start with plugs, wires, cap, rotor, all filters, etc.

 

Yeah, I did all that too.

 

Seems?

I'm not trying to be jerk to you by any means, but "Seems"???

How do you "know" what your fuel situation is?

The simple answer is that you "don't"

You've done everything else and still you have a problem......maybe buying a "T" and placing a cheap fuel gauge in there and taping the cheap gauge to your window while you drive around and monitor the pressures would take you from "seem" to "Know" and you'll stop guessing at that point.

Sunpro FPG is $34.95 at Sears. Has a 6' hose.....100psi .....

 

Welcome to Corvette world. Spending the money on the proper tools will save you tons of money on throwing parts at it.

Spending the money on the gauge may have told you that you didn't need to spend the money on the pump. Even with a new pump and a new filter, there could be an obstruction. Could be injectors, could still be a clogged cat.

These cars really aren't that complicated, but they'll run you into the poor house in a hurry if you're just guessing about a problem and tossing parts at it.

By this point you're no doubt getting very frustrated. Take some time to step back and relax and have a beer. Make a list of things that could possibly cause your issue, then figure out ways to test those without buying parts, there is almost always a way. A calm head and a logical process will prevail.

 

Chevy techs looked at it. They ran it for a long time and said basically the issue was **** gas, combined with factory throttle body settings being out of wack, and it being dirty.

Then he said I should get the Bosch Gen 3 injectors asap, as it'll improve power and driveability even more.

You know what's bad about the chain store I was at? It's an American based fuel company that delivers, and this isn't the first time someone complained.

She purrs now, thanks guys.