LT5 wont run with all cylinders

[Mika73]

I guess many have already read of my problems from CF forum. But problem continues and we dont know whats wrong and what should be tested next when it feels like everything is tryed and tested. It just wont work.

http://forums.corvetteforum.com/sho...283&forum_id=50

Cylinders 2 and 7 wont work ok.

There is not ok spark on cylinders 2 and 7. There is spark, but not like it should. Spark is discontinuous.

Both O2 sensors show full reading (really rich).

I been told that it would be like winning on lotto if both O2 sensors would go at same time.

- Shop manual diagnostics done
- Dis and ECM changed
- Coil places changed
- Injectors tested (Flow ok and resistance 12.3-12.5ohms)
- Cylinders pressure tested about 200lbs
- Sparkplugs changed and plug wires tested

Thanks
Mika

[Kevin]

I was going to say injectors but you said you checked them.

[Tyler Townsley]

Anybody have some frequent flyer miles they can give Marc H to go over and get this fixed? LOL

OK I am going to go through what I would do to get a handle on where the problem is.

1. Get a new sparkplug and pull the plug wire for cyl # 1, put the plug in that wire and lay it on the plenum and start the car. Look at the strength of the spark and then do the same for all the cyl.

According to what you say cyl 2 and 7 should show weak spark, but you need to check them all.

2. Pull the plenum, first make sure the right plug wires are on the right coils, make sure the connectors are tight to the coil pack, you could pull the driver ckt plug and make sure there is no corrosion(Also check the coil conections for the plug wires as they also corrode). Then take the plug wire that showed the strongest spark and swap it for the #2 and put the #2 wire on that cyl. Pull the fuse for the injectors put new plugs in each wire ground the plugs and crank the motor, did the weak spark follow the plug wire? Do the same for cyl # 7.

3. Assuming the above did not change the weak spark location, swap the 2-3 coil for the 1-8 coil and repeat the spark test, do the same for the 4-7 coil. If the weak spark stays on the same cyl during the tests then you need to recheck the DIS module and wiring from the DIS to the coil packs.

Note the above requires no elaborate test equipment until you check the DIS and should take no more than about 2 hours.

Tyler

[Mika73]

Hi Tyler

DIS and ECM are changed: No help

Service did change two coils places: No help

They checked plug wires: No help

Sparkplugs changed: No help

Not good spark on cylinders 2 and 7. Problem stays there and O2 sensors show max reading.

And lets think time 4 weeks ago when problem started.. I had got my car back two days ago of headers, rt cats and Corsa install, driven 200km / 120miles after installation.. Suddenly on freeway at 120km/h (75mph) speed car starts shake really bad.. I had 6th gear on.. Shift to 5th did help.. It wont idle ok and wont run ok.. And service finds out that cylinders 2 and 7 dont have good spark and O2 shows max. Something happend on that freeway.. I was only cruising..

What next.. They have pulled plenium many times, but back on and checked again and again..

I forgot to add that fuel pressure is also checked: OK. My other fuel pump keeps little noise, but pressure ok.

[Mika73]

Whats common with cylinders 2 and 7 ? Do those use same coil?

There has to be something common.. Something that did break on that freeway..

[Tyler Townsley]

Whats common with cylinders 2 and 7 ? Do those use same coil?

There has to be something common.. Something that did break on that freeway..

They are not on a common coil. If the cyl are not firing correctly the O2 sensors will show rich, they are sensors and until the car goes closed loop they are not in the fueling loop.

Spark timing starts in the DIS, the spark itself is generated by the coils and carried by the wires to the plugs. The check above should isolate the problem to a specific component.

Does the car run bad from first start or does it start running badly after a period of time? I know its frustrationg for you when we cannot give you the fix but its also very hard for us as we have certain check points when diagnosing problems and without the car right in front of us we loose the ques we use to move on to the next stage. Reading what you wrote concentrates on the spark side but according to your techs everything in the spark side has checked out ok. Something does not compute so its time to recheck what has been done.

Tyler

[Tyler Townsley]

Deleted.

Tyler

[Mika73]

Latest information:

Engine runs ok with headers only. Service did remove catalysts and it runs fine.

My RT cats were used only 120miles.. and two days.

What happend..

[Kevin]

that is weird. I don't see what the cats have to do with a miss

[95ZR1]

What did you do, put leaded gas in that car? I wonder why they kept saying 2 and 7 weren't firing right if the cats were bad.

[Mika73]

What did you do, put leaded gas in that car? I wonder why they kept saying 2 and 7 weren't firing right if the cats were bad.

First question: NO. They dont even sell leaded gas anymore here at Finland. And I didnt use diesel fuel either.. And then back to business. :)

I dont know why 2 and 7 didnt firing right and O2 reading was max.

But everything looks normal after cats were removed.. Engine did run ok with headers only and O2 sensor reading was normal.

I dont know why. They think that I got bad chip that did kill my cats.

I dont know why this all is happening..

Those RT cats did last two days and 120miles.. Its quite expensive.. :(

[Mika73]

Ok.. Maybe its not catalysts...

He did looks inside catalyst and can see through it.. It doesnt look bad.

Maybe it runs now ok when there is no exhaust pressure when there is headers only..

[Kevin]

This is just wierd. Maybe e-mail mark haibeck or Mike Ebert and see if they can help

[W i l l]

Mylzi,

My vote is that there was an electrical gremlin somewhere letting the two cylinders run rich. It could be coincidence that everything went back to normal when the cats where removed. Then again I may be way off base. It just seems that all the facts don't add up. I would ask the 'mechanics' to put the cats back on and see if the problem reappears.

Good luck!


Ok.. Maybe its not catalysts...

He did looks inside catalyst and can see through it.. It doesnt look bad.

Maybe it runs now ok when there is no exhaust pressure when there is headers only..

[Mika73]

I have emailed to Marc. There is not good spark on cylinders 2 & 7. And maybe thats why O2 reading did show max. But it runs when cats & exhaust is removed. Maybe that not regular spark is enought when there is no exhaust pressure at all when cats and exhaust removed. I been told that usually spark has kinda pulse.. My spark comes and goes, its not regular.
Mark thinks that there might be two bad coils, but Corvette service here says he did change coil places.. and it didnt help. I have no idea whats wrong.. Car has been at service 4 weeks. :(

[Tyler Townsley]

I have emailed to Marc. There is not good spark on cylinders 2 & 7. And maybe thats why O2 reading did show max. But it runs when cats & exhaust is removed. Maybe that not regular spark is enought when there is no exhaust pressure at all when cats and exhaust removed. I been told that usually spark has kinda pulse.. My spark comes and goes, its not regular.
Mark thinks that there might be two bad coils, but Corvette service here says he did change coil places.. and it didnt help. I have no idea whats wrong.. Car has been at service 4 weeks. :(

Have him perform the checks I recommeded with you watching or a friend who is knowledgable about car ingnition systems. I agree with Marc H its something in the 2 7 spark ckt. You take a known good ckt from coil to plug and place it in the bad ckt on item at a time until the defective item is found.

Tyler

[Mika73]

Problem FOUND:

There was broken valve spring..

I heard from Marc that this is really uncommon. He saw one 5 years ago..

[cuisinartvette]

Boy, you sure had to work to find that one! Good luck on the fix :thumbsup:

[Z Factor]

Problem FOUND:

There was broken valve spring..

I heard from Marc that this is really uncommon. He saw one 5 years ago..

I have never heard of one breaking until yours. Any ideas as to the cause?

:cheers:

[Patton]

Wait,... on BOTH cylinders?? Talk about "winning on lotto"

Congrats! Boy do I know how great seeing the light at the end of your plenum feels.

[Mika73]

There is broken intake cam on my engine..

Could someone help, please.. :cry:

(Haibeck sells 4 cams set 4000USD)

[wdo-mkr]

There is broken intake cam on my engine..

Could someone help, please.. :cry:

(Haibeck sells 4 cams set 4000USD)

Lets hope they are at least aftermarkets with a larger lope. Good grief. It looks likek you have another cam coming from lotus(cliff) on the other forum. Keep in mind that you should replace the lifters as well under the cam that has broken. Here is a link for you to give you another option for cams. Hang in there.

http://www.lt5-parts.com/library/catalog/product_view.asp?prod_id=9126&cat_name=Top+End&cat_list=4785%2C%7CTop+End

If either of those deals fall through, I have a set of stock cams sitting on the shelf with only 30k miles on them as well.

[Mika73]

Thanks :cheers:

Yes. Cliff did send me cam. It leaves from UK to Finland at monday.

Lingenfelter also had cams.

[Z Factor]

So did you ever get an answer as to what the probable cause to this mess was? How are things coming along?

:cheers:

[yellowz]

hey mika
i no u said you swapped the coil positions but the gm # is the same for all 4 ib be willing to bet that you have a bad coil why not replace the one thats bad???
i would think if it were bad at 2,7 then you swapped it at another position it would do the same there???.2 years ag at carlise i had a canadien zr1 and his owner come done to fix a problem he had many issues bad tensioner,2ndary vac pump leak and it would run but you could feelit running on 6cylinders after gordon recheck the problem it was a bad coil,his was missing and not firing after we put the coil in took it for a blast up i81 the kid was all excited and thrilled.
I still think you have an electrical issue ,if you replace the coil while you are there although expensive replace the coil module.:happy1:

[Z Factor]

Any updates?

:cheers:

[Mika73]

Car is running now. Thanks to Haibeck of all help :cheers:

[Aurora40]

Car is running now. Thanks to Haibeck of all help :cheers:
Cool! So what was the problem?

[cuisinartvette]

fwiw, www.nelsonracingengine.com can get cams made to any lobe and hardness. I belive they are $2500/4. May want to contact him for specific info.

[Mika73]

This..

http://forums.corvetteforum.com/photopost/data/1052/12246syksy_05_112-med.jpg

:thumbsdo:

[Patton]

Wow,... that would have taken some serious torque to snap like that. I am still rackin my mind trying to guess as to what would have caused that, other than a manufacturing flaw (crack, bubble, etc...) that just eventually gave out. Thats my rational guess, those bad boys dont just break like that.