2.7 misfire, need help

[stupidwhitecat]

Hello, need help tracking down a slight misfire. Bought a 74' targa 2 months ago. Note a slight misfire. Most notable when cold, it does seem to lessen slightly once up to temp, but still there. Noticable at idle and when holding 2nd or third gear at a steady 2 to 3000 rpm. Slight hesitation/miss noted. Seems to rev and pull good. Noted a small amount of arcing between the plug wires near the distributor. So I just went ahead and did a basic "tune up." Replaced the plugs, wires, cap, rotor. Coil is less than a year old, didnt change that. Previous owner sent the CDU out about a year ago, tested and rebuilt. Engine has 130k. Rebuilt around 20k ago. I'm questioning the harness. The previous owner did several splices off the harness. He left the plug for a different type of coil on. I'm considering getting a new harness from partsklassic to start fresh. Any other ideas? Tried to take a video. Was not really cold as i pulled it out to wash it. Can hear the miss a little better in the 1st video when the engine is a little colder. You can also see part of the wiring harness splice job.

Video 1 slightly cold

https://youtu.be/jiaIJf9axl0

Video 2 warmer

https://youtu.be/W7qyGjHP5iI

[Bob Kontak]

Originally Posted by stupidwhitecat

Can hear the miss a little better in the 1st video when the engine is a little colder.

Near the end of the 1st video when you took it to 2000RPM or so, the inconsistency/miss sounds like it is coming from the exhaust and not the engine. Kinda like a secondary burn inside your exhaust?

The putting noise is not consistent with the rpm of the engine. The engine sounds really good, also.

I realize these sounds can get distorted so I may be full of it.

I have had a noise like this on my 81 CIS. It drove me nuts and ended up being the #4 intake runner to head flange being a little loose. Was sucking air.

I would get some carb/brake cleaner with one of those plastic nozzles and squirt a little around the base of the runners while idling to see if the RPM changes.

There are other methods where you pressurize the inside of the intake and check with soapy water for bubbles but the carb cleaner is a pretty quick test.

Side note - In 45 years of piddling with cars I have had one flare up with carb cleaner looking for a vacuum leak and the "fire" lasted two seconds. It's a quick flash and gone. If there are pools of gasoline laying on your engine tin don't do it, but I doubt that is the case.

Report back what you find.

How much does the car smell rich just as a side question?

[mrrolleyes]

why is your idle so high? it might be more "hearable" if you drop the idle to 8-900.

i fought this for a while with my car. ended up being a clogged injector.

[Bob Kontak]

Originally Posted by mrrolleyes

i fought this for a while with my car. ended up being a clogged injector.

Very plausible (I watch Mythbusters hence the use of the big word ). Even a partially clogged injector.

Pull plug wires one at a time and see which impacts the cars operation the least for starters.

[mrrolleyes]

also with the harness issues...

when its running. move the harness around with your hand and see if it cuts the motor in and out. it might be a ground wire thats faulty.

[nomore]

I have this same car. Sounds pretty good, mine has some weird missing type sound about the same as yours. Like Bob says though it seems exhaust or header more than engine, like a leak. Very subtle and doesn't seem to affect performance. One question I have is. Are those condensors
around the coil? They probably shouldn't be there. Nice car.

[stupidwhitecat]

Thanks for all the suggestions. One thing I forgot to mention (and the whole reason for the post) was that my little tune up had no effect on the miss.

I will definitely start by trying the carb cleaner around the intake and individually removing plug wires one at a time. And report back.

Idle is high in the videos as I was using the hand throttle. It idles right under 1k rpm warm.

Tried jiggling the harness, that didnt have any effect.

It smells pretty rich cold. Not really noticeable warm. That is another thing on my to do list. It has a little bit of a rough time with true cold starts. Takes about 2 tries to start when its been sitting for a few days or longer.

[T77911S]

take a look at the plugs and see how they look.
check intake bolts.
I would pull the injectors (with lines attached) and place each in a container.
then run the pump and push up on the sensor plate. then compare the fuel flow of the injectors.
I would also run the pump and see if any leak with the sensor plate closed.
check spray patterns also.
replace injector Orings

if you see a plug that is different, swap injectors and see if the problem moves,

me, I would pull the CIS and replace sleeves and all the rubber parts and put new injectors on it,. "I" would also consider having the fuel distributer rebuilt (depending on flow test results). you can also remove the injectors (if the flow is bad) and compare the flow out of the FD to see if that is bad.
while at it I would check fuel pressures to see what they are.
if it smells rich it could be an injector, wrong fuel pressures, or just not set correctly. also, if rich it usually surges at idle. depending how rich it is.

but start with the plugs

[Dave Kost]

I would start by tossing the troublesome Silver Coil. (Do a search on Pelican)

Try to find a original 30 year old Black Bosch coil.

[stupidwhitecat]

Originally Posted by Dave Kost

I would start by tossing the troublesome Silver Coil. (Do a search on Pelican)

Try to find a original 30 year old Black Bosch coil.

Im aware of the issues with the new bosch coils. This one is 4 months old, so really doubt it is bad. But definitely something I'm thinking about down the road.

[stupidwhitecat]

Originally Posted by T77911S

take a look at the plugs and see how they look.
check intake bolts.
I would pull the injectors (with lines attached) and place each in a container.
then run the pump and push up on the sensor plate. then compare the fuel flow of the injectors.
I would also run the pump and see if any leak with the sensor plate closed.
check spray patterns also.
replace injector Orings

if you see a plug that is different, swap injectors and see if the problem moves,

me, I would pull the CIS and replace sleeves and all the rubber parts and put new injectors on it,. "I" would also consider having the fuel distributer rebuilt (depending on flow test results). you can also remove the injectors (if the flow is bad) and compare the flow out of the FD to see if that is bad.
while at it I would check fuel pressures to see what they are.
if it smells rich it could be an injector, wrong fuel pressures, or just not set correctly. also, if rich it usually surges at idle. depending how rich it is.

but start with the plugs

Plugs looked ok, but they were older so I put in new ones anyway.

Now that you mention surging, I'll have to check out the fuel system too. That is the first thing I noticed when I cold started the car after doing all the ignition work. I had never had that issue before. Small 2-300 rpm surges, reminded of symptoms of a vaccuum leak. This eventually went away as the car warmed up. I took the video shortly after that and as you can see the idle was steady then.

As a side note, I see you're in Myrtle Beach. I am up in Wilmington. Any trusted shops you use in the area for work ?

[gomezoneill]

Pull the injectors lift the fuel dist sensor plate and check the spray pattern of the injectors.

[stupidwhitecat]

So had a little time to check some of the above recommendations over the weekend. First I checked all intake bolts. A few snugged up a little, but none were really loose. I tried the brake cleaner. This definitely had an effect. Mild on #2 cylinder, pretty significant on #3 to the point the engine almost stalled. Like I said bolts weren't really loose to begin with, need new gaskets? Didn't get a chance to check the injectors yet.

[stupidwhitecat]

Update: Using above suggestions thought I found the issue. Using brake cleaner spayed at base of each intake runner. Both #2 and #3 caused the engine to almost stall. So I removed all 3 of the intake runners on that side. I checked the intake runners and the heads. Both were clean. No signs of damage to the gasket. Gasket looked pretty new, which goes along with the history I was given (engine rebuilt ~ 20 k miles ago). All 3 easily removed in one piece. Made sure the mating surfaces were clean. Reinstalled new gaskets along with a "liquid gasket" as well since it seemed there was a leak with the gasket installed dry. Reinstalled each runner in reverse making sure to torque down bolts correctly. Let the liquid gasket cure 24 hours. Started up. No fuel leaks. Still "missing." Sprayed cleaner again. Now around #1 and #3 cause a stumble. What am I missing?

[T77911S]

how did the sleeves look that connect the runners to the air box.

injector seals or injector sleeves leaking.

I do all my work myself.

[stupidwhitecat]

Originally Posted by T77911S

how did the sleeves look that connect the runners to the air box.

injector seals or injector sleeves leaking.

I do all my work myself.

Rubber boots looked good, checked for cracking. I pulled the injectors and replaced the o rings. Didnt replace the sleeves. Not sure they are DIY replaceable? It looks like they are pressed in and there are pre-formed tabs on the manifold holding them in place.

[Walter_Middie]

they are pressed in and there are pre-formed tabs on the manifold holding them in place.

A Dremel tool makes quick work of those aluminum tabs holding the sleeves in. Piece of cake.

[T77911S]

don't know if you checked the new plugs to see how they looked.

you can have a smoke test done if you suspect an air leak.

me, I would pull the intake and replace all the rubber, including the injector sleeves, put in new plugs, cap and rotor, check the fuel pressures, check timing then set mixture. but that's just me.
I would also buy a hand vacuum pump and check all the CIS components for air leaks along with the long vacuum hose (and booster) for air leaks.
I did all this on my 77. spent a lot of time with it. that's how I really learned how CIS works.

you can try moving the sensor plate up and down to see if the idle gets any better,