LT5 miss at all speeds

[Big D]

Hi all, my 90 ZR1 is missing/rough running at all speeds especially when it reaches operating temp. Turning the poser key on and off made no difference. I get spark at all plugs but when I pulled the #3 wire the idle didn't change much. Let her cool down and pulled the plug and the plug showed little evidence of firing. Didn't smell much of fuel either. Pulled a couple of others and they looked good. Next step was to check injector resistance and it was as follows: 1:15.3, 2;14.5, 3:5.7, 4:14.7, 5:13.0. 6:17.8, 7:15.1 and 8:17.3. I replaced the #3 plug and still the same. this time I checked the injector resistance when it was still hot and got the following:1:18.2, 2;19.8, 3:8.0, 4:19.8, 5:11.0. 6:20.6, 7:18.8 and 8:20.4. Now I'm thinking maybe a bad injector at #3 and maybe #5. If so, looks like I'll be pulling the plenum for the first time, what fun. Any suggestions would be appreciated
Big D
'90 ZR1
'69 L46/M21

[TomZR1]

Change your coil packs,I had same problem.IDID all the tests,fuel pressure new plugs wires,even thought bad gas,

[Dynomite]

Originally Posted by Big D

Hi all, my 90 ZR1 is missing/rough running at all speeds especially when it reaches operating temp. Big D
'90 ZR1
'69 L46/M21

Welcome to the Forum

Injectors need replacing

[tomcat]

I agree with all the above posts. Take your time, their are folks in Oregon & Washington that can help you.

Manfred E.......
91 #906

[Paul Workman]

Jon at FIC can set you up with a new set of stainless injectors and gaskets and seals (Gaskets c/o Jerry's Gaskets, BTW). I use the Accel #150821s (from Summit Racing) with no complaints for 4 years running now.

Note: As for coil packs, I installed fresh coils with GM coil (direct replacement) "while I was in there" too. (When in doubt of what the readings should be, I measured resistance on both the primary and secondary windings, looking for consistency. However, one of the coils measured "open" between output terminals, so I replaced the all. All the readings then were the same across the lot, and the car runs great!) That was 6 years and 20k miles ago w/ no issues with them since.

[Big D]

thanks everyone for your inputs. Looks like I will be going under the plenum for the first time. Should be a good time....... Looking forward to getting her running back the way she should.

[Paul Workman]

Entering under the plenum is a "right of passage" for LT5 owners, it seems.

Might consider R&R'ing the started solenoid high-current contacts; set ya back around $10 or so.

Plug wires?

Vacuum lines, check valves, rubber unions = OK?

Secondary actuators and linkage works OK?

[Dynomite]

Originally Posted by Big D

thanks everyone for your inputs. Looks like I will be going under the plenum for the first time. Should be a good time....... Looking forward to getting her running back the way she should.

Removing Plenum (including the 10 minute Plenum Removal)

Do as Paul suggests and clean the Valley Drain under the Starter when you are there. Other "stuff" in my signature

[Big D]

Looks like I'm going to go with the injectors from FIC. Can anyone suggest which brand of coils I should go with and where to get them.

thanks again everyone,
Big D

[efnfast]

OEM coils. Get them from Jerrys Gaskets.