I recently purchased a 1984 Corvette 350/auto with the Z51 suspension. I'm having trouble with the cross fire injection. When I first start the car it runs rough and idles poor after about ten minutes its ok to drive. If you don't wait for the idle to straighten out the car will just stall out every time you touch the gas or give a rev almost like it's trying to catch up to itself. Sometimes the car runs perfect not a problem plenty of power then other times it bogs and just doesn't have any power. I changed the fuel filter, plugs wires, cap and rotor, spark module in the dist has also been replaced. Two more things will the saw blade wheels bolt right onto this car? And would it be worth changing to TPI. The car has 92,000 original miles. I also own a 1977 Corvette 350/4 speed 65,000 original miles the 77 feels much faster then the 84 shouldn't that be the other way around? Thanks for help, Bill[IMG]http://[/IMG]

 

I own a 76 and a 84, and yes, the 84 is much faster. Have you checked for any vacuum leaks. Sometimes, when the motor warms up, the hoses expand just enough to lessen the leak. Other than that, CFE would be the one to help ya there. Of course, you should know that you need to buy the Helms manual first.

 

Check for vacuum leaks. The manifold lid is notorious for leaking. It may have a small leak that seals once the motor heats up. Synchronizing the TBIs is another item. Take the IACs out and make sure the pintles are clean. Hook up a timing light and shine it on the injectors as they spray. The pattern should be cone-shaped. If taken care of, the Xfire is a very reliable motor and induction system. With small DIY mods, it is more powerful than a TPI motor. Go to www.crossfire.webhop.net for a community of Xfire Vette owners. www.thirdgen.org is also a great site for dealing with TBI motors.

 

Manifold lid?

 

Sorry about that, anyway I changed all the vaccum lines (that was my first thought) I also checked the EGR working fine and I reolaced the map sensor on the firewall.

 

replaced the map sensor

 

You do know that the manifold is a 2 piece on the Xfire? The TBIs are mounted on a flat lid that bolts onto the manifold base. The gasket sealing the lid to the base deteriorates and leaks.

 

no, I had no idea ....is it a difficult repair? I've already replaced the electronic cluster and some other odds and ends

 

http://www.crossfire.homeip.net/cftest/faq.asp. Also get a shop manual. Replacing the lid gasket isn't difficult. Might take 1-2hours and then let sealant cure.

 

Thank You. I hope it works.

 

Please mind that the CFI will wet the plugs a lot of times when started cold. Than the engine runs like crap, misses a few cylinders and really has to become hot in order to clean the plugs. I have it a lot of times when I start cold an hit the pedal too much.

 

Interesting.... I've never had a problem with fowling plugs when cold..

As Dom said, check the TB lid and also the TB gaskets and make sure the TBs are balanced. You will need a manomenter to balance the TBs which you can make with a yard stick and some 1/4 inch clear tubing. Here is a link to the procedure at the Crossfire Forum. You can also do a search there on what the manometer looks like. Just follow the procedure.

 

What mods were needed to get your 84 into the 13's? I just purchased this car and really like it. It handles great and really has a nice feel. The car was just painted 3 months ago by Kerbeck Chevrolet Firemist Black..Car still has all the original exhaust nothing has been molested.

 

I have a mild 383 with TFS heads and a XRam on top with bored TBs @ 2.13 inches. I have just recently put in a Vette 89 700r4 with some goodies and a 2600 stall converter from Edge Racing Converters. I hope to have it back on the road the weekend. I just need to hook up the exhaust and a couple of odds and ends. She has had one run at 12.95 @ 106mph recently. But that only happened once because of a tired 700r4. Hence the trans swap. Needless to say 12's are in my future. I use a 1227747 ECM from a 88-93 TBI truck for tuning.

I highly recommend the Crossfire forum for info. Great bunch of people (as with this forum) and lots of good info. And as you can imagine a few opinions.

Here are the motor specs.

Block - 95 4 bolt roller
0 Decked
Quench Distance - 0.039"
Rotating Assy - Eagle stroker kit (Crank, Rods etc)
Speed Pro Pistons with -12.5 cc D Dished
Moly Rings
Internally balanced
6 3/4 Inch harmonic balancer from Summit
Scat flexplate for late model block
Heads are TrickFlow 195cc intake runners with 64cc chambers
Compression ratio 10.4:1
Cam - Compcams CS XR269HR-12 (pn 08-502-8)
Duration @ 0.05 218/228
LSA 112
Lift with 1.5 Rockers - .495/.503
Lift with 1.6 Rockers - .528/.536 (I did this)
Summit Roller Lifters
Aluminum Roller Rockers 1.6 ratio (from ProComp in Australia)
XRam with 2.13" TBs and 90 lb Injectors (454 Truck)
Headers - 1 3/4" Tubes, Exotic Muscle (www.exoticmuscle.com)

I like my 84 alot as well. The best part is keeping up with the folks who snub their nose at the 84 (please no debates) and beating them from time to time at the track.

 

HT',
check out the Crossfire and Thirdgen websites.

Some of what you describe are 'computer design
issues', such as, decel fuel cutoff, decel fuel enleanment,
desired idle speed, idle stall catcher,
desired open loop a/f ratio, etc....
assuming you don't want to mess with
the computer...

check for vacuum leaks,
try disconnecting EGR / for a test,
check for leaking or imbalanced fuel injectors,
ensure that the spark plugs are perfect,
try lower octane gasoline

IMO, the General, probably for reasons
of emissions and fuel economy,
made some 'driveability' tradeoffs
that push the car to a tendency
to stall, that is just the way it is,
anything that will help driveability,
will reduce stalling.

 

Silver 84,

The Xfire certainly had its share of compromises. Like the size of the ports on the intake side of the cylinder heads, not to mention the heads themselves. The quirky staggered injector setup to make up for the drop in FP between the 2 TB's. But for the most part, the car runs pretty well and if it isn't, then the problems are pretty much like any other SBC. Its a vacuum leak, or plugged fuel filter or something like that. The injectors or IACs may need to be cleaned. Put a timing light on the car and shine it on the injector spray. Try putting the induction lead for the timing light on #3 CYL, I think it works better for the injectors. See if the spray pattern is conical or is it sputtering out. The Xfire manifold uses heat to help vaporize the fuel. Unlike the TPI, the Xfire is a wet manifold. So the hotter the motor the better the atomization which is why it drives better when its warmed up.

 

You need to test the coolant temp sensor in the front of the manifold, and also the TPS, these are 2 likely causes of your probs.
84's are cool, hope you have fun with it.

 

Ben brings up a very good point. Swapping out all the old sensors really helps. After a while, they're not as accurate. Although they may not throw a code, they could be inaccurate enough to make it difficult for the ECM to optimize operating params.

 

I would check for codes first. Changing the sensors is a good idea too. Fuel will puddle at first on cold start, especially when cold outside. Let us know what you find.

 

Ok, I pulled both idle speed motors and cleaned them they were very dirt. I cleaned both throttle bodys and checked for vaccuum leaks..nothing found. I did find a bad vaccuum line to the mass air sensor on the firewall. I replaced all vaccuum lines. I started the car and let it warm up seemed ok but after sitting still had a poor cold start. I went ahead and removed the dig cluster to send it out for rebuild..I disconnected the battery prior to removing. Now, when I reconnected the battery I started the car cold and the idle worked perfect..after about two minutes the car stalled out. I restarted and was back to the poor idle condition. Once the car is warm and is driven and parked on the restart it searches for an idle up and down until you hit the gas pedal and then its fine. Also under full throttle at highway speed it seems as though you hit a wall..when you take your foot slightly off the pedal the car starts to pick up again almost as if its holding passing gear to long...Thanks for any help you can give me. I would like to keep this car original if possible I think it might be better to just go with Tuned Port..