I have an 1989 C4 with the L 98. Last summer it started to run rough, and I started my search for the problem. I changed the cap and rotor, I found the center post going to the coil all but gone. Problem got better but still there. I changed the plugs. No luck. I just took it out of storage from the winter and put a new coil in it. Problem is still there... It feels like it is running on 6 cylinders. I just bought new wires.... They will go on tonight. Has anyone experienced this? Any sugestions? I'll have to admit my next thought is fuel injectors, and I have never done anything with those. Any suggestions / ideas would be greatley appreciated. It's making me

Thanks,

Rick

 

First I would check for codes.

 

If you suspect a fuel problem, this may very well be, I would use a fuel pressure guage to check pressure at the schrader valve on the passenger side fuel rail. With guage attached turn on key to prime relay and pump. Note pressure and switch key off and watch guage. Faulty fuel injectors or low fuel pressure will give these symptoms.

 

Check the resistances across each fuel injector to verify the injector coils are ok. Starting in '89 (and going through to '92, I believe) they had issues with the varnish on the coils dissolving and causing them to short.

Good luck!

Ben

 

check for codes. Use chevron techron thru your tank once or twice and see if that helps along with premium gas. Faulty injectors as mentioned could be a source but for your sake I hope not thats a real bitch to change. Goodluck

 

Pull the plugs and inspect them, check the fuel pressure readings

fuel filter should be replaced if it hasnt been before

 

I'm no mechanic and don't claim to be but my Vette was acting the same way and I had everything changed as you had and it boiled down to the fact I had 3 bad injectors. I'll be replacing all 8.
Funny thing is I got no codes or lights of any kind lighting in the DIC.
Good Luck
Gary

 

Taitrj: As mentioned above, the 89 stock injectors can be a real problem due to shorting of the coils. To check for this problem, pull each injector plug off the injector and measure the ohms of the injector coil. The readings for the stock injectors should be 16 to 17 ohms. Any reading less than 16 is an injector that is shorting out. A shorted injector will not place the proper fuel in that cylinder.....and she runs rough. If you need to change out the injectors, you can do this without pulling the runners. Send me a note if you want more info on this.

 

My mechanic said the resistance should be 10 ohms. I had resistance on my injectors all over the board. They ranged from 5.5 to 17.3 and everywhere in between. Like I said I'm no Mechanic and don't claim to be I'm just going by what my mechanic said.
Gary

 

Gary: I suggest you contact Rich Jenson at Cruzin Performance and ask him what the resistance on Multec injectors should be. Rich runs a business cleaning injectors and is well respected by many forum members. I had three injectors below the 16 ohm range on my 89 and the engine was running like crap! New injectors solved my problem......and they were not Multecs.

 

I'm having the same issues but mine is a 1991 .

Good luck , PatsFan

 

I believe the years 89, 90 and 91 had the GM Rochester Multecs as stock injectors. Here is a note from Rich Jensen on Multecs:

Hi Bob,

The problem you currently have is that from 1989 through 1991 on the L98 engines GM installed Multec injectors. These injectors have one of the highest failure rates of any injector ever installed. It's not a matter of "if" they are going to fail, it's simply a matter of "when" they will fail. That is why some of your injectors look differently than the others. Some of them have obviously already failed and were replaced. Because of their design they cannot be repaired so the only solution is to replace them.

You can try to find some of the same injectors to use as replacements however they will likely eventually fail also so a better alternative is to replace them with an aftermarket set of replacement injectors or find some of the earlier Rochester injectors that were used from 1986 though 1988 on the L98's. These were a Bosch design injector and they don't have the problems that the Multecs do.

I don't sell any injectors so I can't help with supplying replacements but if you do find a set of the earlier design injectors I can service those and they have a very good track record of long life and serviceability. The part numbers you would be looking for are: 1986 = 5235211, 1987 and 1988 = 5235302. These are the part numbers that are on the injectors themselves. They are not the part numbers that would be listed in a GM parts catalog.

Sorry to be the bearer of bad news but that's just the way the Multec injectors are.
Hope this helps. Let me know if you need more info or have additional questions.

Rich Jensen

 

Flyinlow90, you do need new injectors. The difference in Ohms between injectors should not vary more than .5 And I'm sorry, I do believe your mechanic is wrong, 10 is to low, my 87 runs 19-19.5 Ohms, I would think you should run closer to that. What I've also heard is if you find one bad one-replace them all, because the others will be close behind.

 

 

I think the 86 thru 88 models came out with GM (Bosch style) injectors as the 89 was the initial use of the Multecs. The ohm readings will be different for each type of injector. I do agree with Rick that they should all be within .5 ohms of each other......provided they are in good working order. Are we having fun? This forum is fantastic.

 

thanks for all the help everyone. It ended up being 3 bad injectors. pulled it apart and changed them all. Runs perfect again.