I have an 84 350 CID Crossfire which has developed an idle and power issue that I can't seem to rectify. Bear in mind, I am NOT a mechanic and have limited mechanical skills sadly.

The car is stored for 6 months of the year (New York) and has 68000 miles on it. It is a stock vehicle with no engine mods what so ever.

About three weeks ago it began Surging at idle, regardless of whether it was cold or hot, and does this for up to a minute or so before settling down. It will start to idle around 550 RPM then surge between 400 RPM and around 1200 RPM. It is so bad that someone asked if I had a performance cam in it as the whole car rocks.

While I know the Crossfire has a hesitation associated with it from a standing start, mine hesitates severely under acceleration, whether it is from a standing start OR accelerating to overtake another vehicle, almost to the point of stalling or so that is what it feels and sounds like. If I accelerate slowly, there seems to be less of a hesitation.

Things I have done to try to fix these problems (which I am assuming are associated with each other):

Used 93 fuel with fuel additive/cleaner
Replaced spark plugs and wires

And that is the limit of my mechanical skills.

Can someone please give me some suggestions as to what the problem could be. I should mention that these problems seemed to occur over night almost, as if something simply failed.

Any help will be appreciated as the car is terrible to drive at the moment and just sits in my driveway until I can get the issues rectified.

If I have omitted any information please let me know.

Cheers,

Wombat457

 

Sounds like a classic case of vacuum leaks, a common problem with the Crossfire injection system, lots of places to leak. I would start by checking the tightness of the manifold bolts. Don't go crazy and overtighten, just make sure they are snug.

Do this and get back to us with the results.

BTW, is your check engine light on? Any codes stored?

Dave

 

I had a similar issue recently with my new '84. Someone suggested there needs to be more than 1/4 tank of fuel. My experience shows I need to half 1/2 tank of fuel or more to experience no hesitation under heavy acceleration. It has to do with the location of the fuel pump pickup location within the tank and fuel slosh under acceleration.

 

Check for vacuum leaks

Check your fuel pressure.

Do those things FIRST. I bet you find your problem in one or both of those places. I bet it's your fuel pressure as a result of the pump...but buy/borrow a gauge and check it.

Misnomer time:
*there needs to be more than 1/4 tank of fuel
-The fuel tank doesn't need to be over 1/4 full. If it does, something is wrong w/your fuel pick-up.
*The Crossfire has a hesitation associated with it from a standing start
-That should NOT be the case at all. In fact, a properly running CFI car should have some of the best throttle response and low end punch you have felt. Running right, they are extremely responsive and have fantastic off the line grunt.

 

You need to pull your codes. Just because the check engine light isn't on doesn't mean there wont be some. Sounds like a faulty tps to me

 

Not a TPS. He said the symtopm is worse with fast throttle application, and nonexistant w/slow application. Not symptomatic of a TPS. Check the fuel pressure and vacuum leaks, first.

 

May be fuel delivery... maybe fuel pump.

http://forums.corvetteforum.com/c4-t...-pressure.html

 

Thanks everyone, I'll check for vacuum leaks and fuel pressure and let you know what comes up. Appreciate the advice.

One point, my car has always been hesitant from a standing start. I bought it with 36000 on the clock (original as I know the previous owner who is a Corvette collector). Perhaps this problem has always been present and I have just accepted it as the norm.

Cheers,

Wombat457

 

Hi Again,

It seems as though the problem MAY be my fuel pump. I have looked through the Forums and many people with the 84 Crossfire engine have changed theirs out for a 1985 model Fuel Pump. This they say has rectified the hesitation issue, smoother idling, easier to start and increased performance.

As such, I looked the specs for both the 84 and 85 Fuel Pumps for the small block Chev motor (specifically the 350CID 5.7ltr). The following is what I discovered:

84 Model Fuel Pump:

has a 17 - 23lb pressure fuel flow

85 Model Fuel Pump:

45 - 60lb fuel flow

This is a considerable difference and causes me some concerns. My question therefore is this - Will such a high fuel flow have a detrimental impact on the car? In other words, will using an 85 model fuel pump hurt the car in anyway? Would I need to change other components to ensure compatibility with the Crossfire engine? OR will having a much higher fuel flow pump on the car do nothing at all, in terms of causing other problems?

Cheers and look forward to your thoughts - bear in mind though my car is totally STOCK - NO engine mods have been done to it at all,

Wombat457

 

Replace the fuel filter

 

FIRST TEST. Don't throw parts at it. Don't replace parts based on others' posts...YOUR problem may be diffenent.

You need to get a fuel pressure gauge. Rent one, borrow one, or buy one. Hook it up to your car, in line, between the fuel filter and the fuel line (Passengers side down low front of engine). Read the gauge from idle to WOT read line. If it reads less than 9 lbs at all...pump is faulty (worn out). Report back.




The pump does not manage the fuel pressure. All it does is pump fuel. The fuel pressure regulator is what determines the fuel pressure, (assuming your pump can meet the engine's demand). You can put a pump that has a higher capacity (the "85 pump", or any later model, higher volume, positive displacement pump -doesn't HAVE to be an "85 Corvette fuel pump) and your regulator will still maintain the set opreating fuel pressure. KNOW THIS: if your fuel pump is not the problem, NO fuel pump can help your situation. IOW, if your stock original fuel pump is meeting the criteria (9-13 PSI under ALL conditions) then there is no possible gain to be had by swapping it. Those who worship the " '85 pump" do so b/c they had a faulty/worn stock pump, had issues as a result, replaced the pump and saw fantastic results. There was no magic in the '85 pump, rather, the replacing of the pump, cured an actual problem. I've seen an '84 CFI 'vette run into the 13's on the stock, original fuel pump, so when operating properly, they can perform very well. So test first, then replace what's necessary.

If after diagnosing, you determine that you do in fact need a fuel pump, then buying a later model/higher volume fuel pump is wise; it will likely last longer, and provide a higher ceilling for future "mods". No it won't hurt the car, no it won't require any other mods to work...simply install it and run.

-Tom

 

Tom 400CFI,

Darn, thank you for your response - everything you have said I discovered from a Corvette Specialist in California, none the less your confirmation of that advise is much appreciated.

Okay so an update. As always we tend to look at the worse in most things (as I did with this issue). I had a Vacuum Test done and it came up with NOTHING wrong. I had the Codes checked and again NOTHING showed as being faulty - No Codes to Report. In short, there was nothing wrong with the car at all according to these tests.

To the point - I can report that the HESITATION that I have had for the past three years is now GONE! The problem? A crimped Vacuum hose. New hose put on and bingo - NO more hesitation either from a standing start or at any other speed.

I am going to replace the plugs, wires and fuel filter out of normal maintenance.

A couple of other vacuum lines were plugged up and not connected as well, an ERG Line ??? was one and will be fixed next week.

End result ... a $2:00 length of rubber hose fixed the hesitation and (so far) stalling of the car - my main issue.

Thanks everyone for your advice, especially those who recommended the Vacuum Test - had it not been for that, I would never have found the crimped hose.

I now have an 84 that runs like it is suppose to, and better - much better in fact.

Cheers to all

Wombat457

 

Well that is a great story! I'm so happy that you saw a diagnosis through and didn't arbitrarily spend money on pumps, TPS's etc. Good job.

Can you tell us which vacuum line it was? I'm having a hard time thinging what vacuum line could have cause the symptoms that you were describing...

Thanks for the update!

 

Tom,

I don't know the name of the vacuum line that was crimped but it ran from the MAP Sensor to the injection system. I think the mech said it was the line that told the car when the accelerator had been pushed.

The sensor it ran to was mounted on the firewall drivers side and the line was only about 8 - 10" long.

Not sure if that helps any, hopefully it does.

The other thing that needed adjustment was the TPS. It was set to 0.42 ??? when it should have been set to 0.50 + or - .05.

I have also changed the fuel filter this morning and that seems to have helped as well - the car does idle a bit smoother. I spoke to the last owner who told me that when the car was originally built it was specially built as a ZR1 (I think) without the ZR1 motor. I gather that means it has all of the ZR1 performance handling equipment it with a standard 350. Anyway, that was just a tid bit for the hell of it.

Cheers and thanks again, next week I am putting in NGK Radium plugs (or top the line AC Delco plugs) with appropriate wires as it does have a small mis according to my mech.

Wombat457

 

If you'd like to know which options the car was built with, the build sheet with all the codes are in the glove or console box lid. Write them all down and google for the build codes. When he says ZR1 without the motor he might have meant Z51 or Z52 package, which includes diff wheels, better shocks, oil cooler, bigger brakes (J55), etc.

 

Thanks Tony,

Now you mention it, I do have the build sheet with the manual. I'll take a look.

Cheers,

Wombat457

 

Of course. I should thought of that! Thanks for the feed back...and enjoy your CFI the way its supposed to be!