Help with tune up

[Timbalero]

Just bought a 95 with 143000 miles on it. Runs real rough. Lot of backfiring and misses. I am not getting any codes in the dash. I replaced the plugs, still running rough. I am replacing the wires today. What is the easiest way to find out is the firing order is the right one? What else should I replace?

 

[Aurora40]

I believe the OEM coil packs have the cylinders numbered on them. So that or checking the factory service manual would be the way to check the firing order.

While you have the plenum off, you may want to check the injector resistances, though I don't think the '93+ injectors tend to go bad. Also a good time to check out the secondary vacuum system.

 

[Timbalero]

Thanks

 

[90 Corvette ZR-1]

is the MAP sensor hose on?

 

[Timbalero]

I don't have a tec manual yet so where is the map sensor hose located?

 

[90 Corvette ZR-1]

back of the plenum there should be two hoses running to a block that is screwed into the plenum.

 

[tomcat 74]

Help with Tune Up

Just bought a 95 with 143000 miles on it. Runs real rough. Lot of backfiring and misses. I am not getting any codes in the dash. I replaced the plugs, still running rough. I am replacing the wires today. What is the easiest way to find out is the firing order is the right one? What else should I replace?

Hi,
You can check these websites http://zr1netregistry.com/ & http://www.pnwzr1.net/ there are Maintenance & tech help at these websites
that can help you.

Tomcat 74
91 ZR1 #906

 

[Hib Halverson]

A couple of observations, here...

First, you said the check engine light is *not* on, which, if true, is a good thing. However, with a car with that many miles on it and running as poorly as it is, I'll assume the possibliity that the check engine light bulb has been removed.

Does the check engine light blink on during the "bulb check" portion of the engine start sequence? If so, all's well with the MIL. If not, you first need to see if the MIL even works.

As suggested elsewhere, do check the MAP sensor hose. The map is under the rectangular aluminum plate at the back of the plenum. A hose runs from the bottom of the MAP sensor to the rear of the plenum. If that hose is off, the check engine light may be on.

With 143,000 miles and running like crap, I'd not only change the plugs, I'd put new wires on it, I'd check the coils and I'd run the fuel pressure checks in the service manual which tests for leaking injectors.

Check the tightness of the two engine controls grounds at the back of the block.

Test the secondary port throttle system for vacuum leaks.

I'd even go as far as to run a cylinder leakage test.

Lastly, when you go to buy a "tec manual". Do not buy Haynes or Chilton. They're useless to those working on the LT5 engine. Unfortunately (because they're expensive) you must have the two-volume, factory service manual.

 

[Rob]

As Hib suggests above, one of the things you should do is conduct a secondary port vacuum system check. You can read about doing that here:

http://corvetteactioncenter.com/forums/showthread.php?t=14272

Good luck and keep us posted!!

 

[jonszr1]

If one wanted to do a leak down test whAT WOULD BE a good % on the test and does one do it hot or cold and should a compression test and what should the cranking compression be . just trying to learn

 

[Hib Halverson]

If one wanted to do a leak down test whAT WOULD BE a good % on the test and does one do it hot or cold and should a compression test and what should the cranking compression be . just trying to learn

Do the leakage test hot. Make sure the air compressor you use can supply the pressure and volume required by the tester. The tester's maker will usually list that spec. its the instructions.

A engine in outstanding condition will have less than 3% per cylinder. A very good engine will have 3-5%. OK engines will be 5-10% Higher than 10% means it's time to diagnose a problem.

The factory service manual has the information you need on compression testing.