Dano84

I'm new to the Corvette world and defintly new to the crossfire injection. I have 84 Corvette my problem is when trying to accelerate the car stumbles for a moment and then clears itself. It idles a little rough but not to bad just a little. It's has new plugs, wires, cap, and rotor. I just bought this car and I don't know a lot about it. Any help would be great.

fredd1

Getting the factory service manual and checking the trouble codes off the obd1 connector would be a good start in diagnosing your problem. The connector is just under the dash above your right knee (it may have a small rectangular black cover). You can turn the ignition key to on and short pins A & B on the connector with a paperclip and read the the codes by counting the flashes on the check engine light. The first code is always a 12 (one flash followed by two flashes) repeated three times. This is the delimiter at the start and end of the actual codes. Do a search on diagnostic codes on this forum to find out the meaning of the various codes returned. You can also follow the troubleshooting guides in the FSM for various ignition/run conditions to narrow the problem down. Throwing new parts at the problem is probably the most expensive way of solving ignition/run/fuel issues.

ToniJ1960

You didnt mention fuel filter and air filter?

Hot Rod Roy

Vacuum leaks are a common problem with the Cross-Fire intake manifold. There are a bunch of small bolts around the top perimiter of the manifold that should be checked for tightness. The gasket surface in this area is pretty skinny, so that's a potential area for vacuum leaks. Snug down the bolts at the bases of the injectors, too. Do not remove the injectors from the manifold top plate, or you'll mess up the balance calibration of the injectors!

Are the adjusting screws for your injectors still welded into position, or have these already been tampered with by a previous owner? How many miles on the car & engine?

Tom400CFI

Check for vacuum leaks, and check fuel pressure, for starters.

Dano84

There are no codes. And after looking at it a little closer after work today there has been at least one idiot besides me working on it before. I'm going to have to correct quite a few previous repairs before I can start fine tuning it. I found vacuum lines, wires, and all kinds of little crap that has been messed with. I just hope the previous owner quits working on cars. I know why I got it so cheap.

Thanks everybody I'll let you know what I find.

bogus

the xfire does require a strong attention to detail...

When it is right, it runs pretty good... but when it's wrong... God help you.

As you progress through modification, keep this in mind... updating the to SEFI is not that crazy an idea....

TerryOlson

I'll be watching this thread closely - our '84 generally runs great, but I notice the same hesitation described here. The TBs were rebuilt by a specialist just before we bought the car so I don't think the problem lies there in our case. I'll be checking the manifold bolts next and watching for other advice as it comes in.

Tom400CFI

^Check your fuel pressure too, please.

DUB

THIS is BIG issue...and many do not because it takes a bit to do correctly due to the car does NOT have a fuel test port.

Usually low fuel pressure will show as a 'hunting' or an idle that goes up and down.

More SPECIFIC information needed from you.

Please ANSWER all questions...due to they are important.

I am assuming this engine is still factory. (yes or no)

Roughly...How many miles on it?

Automatic or 4+3 manual???

REALLY IMPORTANT!!! Is your Corvette stored in a garage or is it out in the elements???

I am NOT judging you...but what grade of fuel do you use??? and is it a name brand or off name stuff???

When you start it and get it running the FIRST time in that day. What is the RPM????

And at this RPM...how is it running??? 'hunting' or going up and down in RPM, steady rpm, rough idle. etc.

IF the RPM is high when you FIRST start it (1200-1350)...how long does it take to begin to idle down to 700 RPM...IF it does it at all.

I know you may not want to hear this...but it is what it is. And if specific 'things' are not in line and correct...and just turning screws with a purpose can cause other problems.

The engine should be idling at 500 IN GEAR( automatic)...when it is at operating temp....and roughly 700 RPM in PARK or Neutral (automatic)

Timing issues...EGR valve issues, vacuum leaks, throttle body shafts being worn out, coolant temp sensor issues, MAP sensor issues, Bad ECM (computer)...either grounds going to it or power going to it. Throttle position sensor not adjusted correctly (possible)...Oxygen sensor being bad or the wire has melted to the exhaust or is grounding out on something metal somewhere...and low fuel pressure. ANY exhaust leaks at the engine and OR in front of the Oxygen sensor, plugged or restricted Catalytic converter....but that usually will restrict the power the engine can produce....and can glow cherry red...(unlikely)

A voltmeter or scanner would help.

As mentioned by ToniJ1960...air and FUEL filter. A fuel filter does 2 things...aids as a moisture trap and filters the fuel. Should not be taken for granted.

Your repairs do require you to do the BEST possible in fixing the previous owners crap.

I repairs Corvettes like this quite often for a living. And ONE thing I can write....that most people do not know about....is that when dealing in a electrical issues....MOST PEOPLE use SOLDER-LESS butt-connectors....which I do not. It is a fast and easy method for wiring repairs. Which being stranded out in the desert....trying to get home....it is fine. But for me I can not tell you how many Corvettes I have to repair where someone used a solder-less butt connector...and when they crimped it...they squeezed it so much that they actually effected the integrity of the strands of wire...which in most cases...I find them BROKEN at the crimp. This is why I ALWAYS SOLDER and use shrink wrap.

To each is or her own...and do as you wish...but I am one who does NOT have the time to chase electrical 'demons'...only to find that taking the easy way out is what is coming back to haunt me. I LEARNED that a LONG time ago.

DUB

garryowen

dano

this might get me flamed but here is how i check my fuel pressure.

most say to tap in to cross over between throttle bodes.

when i rebuilt my throttle bodes, i found the line from the fuel filter goes to the first , rt hand, throttle body to the second T B via an open chamber that the steel fuel line is flared and attached to both T B.

my car has a hose clamp type fuel filter just under the ac-heater housing on the frame. goes from there to first T B with the steel fuel line.

by loosing the out put side of filter and inserting a tee, was able to use a fuel line hose to bring to top of engine and in stall a gauge. this was easily read from dr seat both running and driving.

simple matter to use rubber fuel line and hose clamps. not permanent but easy to hook up and un hook. more so than brazing a fitting in the cross over lines between the T B.

mine runs at 13.5 psi.

GQ-ROD

I did all the below items when i got mine, been driving beautifully for the last 2 years.

1- Do a compression test.

2- Do a proper tune up with all OEM parts,

do not use the acdelco #2 platinum plugs they are smooth and the wires will come off the plugs. Use the acdelco stock copper plugs they have ridges as do the oem wires which help keep them seated. Gap them properly !

3- Very important rebuild your distributor using acdelco or gm parts, the reluctor wheel could be cracked and you would never know it by looking at it since the cracks are hairline thin, it will fall apart in your hands when you remove it. Install a new ignition control module, acdelco brand. You are not throwing parts at it, this is simple logical basic maintenence for an unknown car.

3a- DO NOT overtighten the screw that holds the ignition coil to the grounding strap in the distributer cap or guess what?.....you guessed it you will get misfires, poor idle etc etc.

4- DO NOT use anti seize on the plugs, this will create misfires, rough idle, hard starting, poor running and no power.

4a- YOU MUST correctly find TDC and set your ignition timing properly do not go by the factory timing mark as the previous owner may have improperly set the timing.

5- Replace your fuel filter and hoses, once done, check your fuel pressure, as has been mentioned install a tee, and use the actron fuel pressure gauge, it has a valve that lets you dump fuel into the hose and recheck pressure without disconnecting it to dump fuel.

6- Upgrade your fuel pump to the 85 corvette one, or the walbro sold by racetronix.

7- Buy the factory service manual .......you will need it as all answers to questions here begin with " do you have the FSM " lol.

8- Replace your fuel pressure regulator with the borg warner or acdelco-again it's basic maintenance on a car this old.

9- Test and adjust your throttle position sensor. adjust if necessary, per you guessed it ..........the FSM.

10- Replace your air filter.

11- Test your MAP sensor ( not MAF sensor ) replace if necessary.

12- Replace the hose to the map sensor.

13- Replace your coolant temp sendor to the ecu at the front of the engine with the upgraded one, you will NOT find the original temp sendor socket.

14- Check for vaccuum leaks, replace all vac hoses even if they are not leaking with new thermoid vac hose, cheap insurance against future issues.

15- Don't forget to wave ! and enjoy your ride.

Tom400CFI

No one should flame you for that; that is the best/fastest/cheapest way to get it done.

Motoguy58

I'm new to the Corvette world also. I did a tune up recently and for the most part it runs much better smoother & increased power than before. I did pick up a just off idle hesitation that was not there before. I did put a small amount of anti seize on the plug threads. I see in a previous post this is a no-no. What's the reasoning behind this ? Loss of ground or what? Just trying to understand. Thanks

GQ-ROD

I also learned the hard way with a bad misfire related to a host of things when i initially did my tune up when i first got my car, the reason anti seize on spark plugs into IRON heads is a no no is because it prevents the spark from grounding through the plug to the heads from the spark threads, it also creates a bridge for the current to flow ON TOP of the ceramic portion of the plug and to the head RATHER than through the plug, across the gap then into head.

On aluminum heads it is still ok ALTHOUGH there are certain spark plug makers that stipulate that their plugs ALREADY have an anti seize coating on them to prevent seizure, so some do not recommend it anymore.

I had posted a long you tube video that goes into great detail about this in another thread ( can't remember which now ), i installed the correct copper plugs after having cleaned each spark thread hole of any anti seize and have not had any issues since going on a year now.