Nagging skip

[bobcat]

I'm sure my issue has been addressed probably multiple times on this forum but after a brief search I found no definitive answers. I have a 96 cobra that aside from a cold air intake and cat back exhaust is stock as far as I know. I bought the car about a year ago from a stranger so it obviously has an unknown maintenance history. I purchased it to restore and fully expected to run I to some issues. Currently the car has a nagging skip issue under load howeveritruns well when I'm just tooling around in it and don'tkick it in the butt. I have preformed a full tune up which included new plugs, wires and filters. For peace of mind all fluids were drained and replaced. Skip remains. Replaced coils. Skip remains. Replaced fuel injectors with the stock 26lb blue top injectors which was what it had in it. Skip remains. Preformed a fuel pressure test and here's what I got. 30psi with ignition on and engine off. 35-38psi at idle and vacuum connected to regulator. Pressure goes down to around 28psi at wot (seems like it should go up). Dis- connect the vacuum from regulator and pressure holds at 40 psi regardless of throttle position. I'm an old school knuckle buster that's far more familiar with carburetors than fuel injection so any advice is appreciated. There is definitely a solid peace of mind from knowing first hand all the parts I've replaced but the irritation is real when I can't seem to rid my car of to demon. Thanks in advance for any help

 

[RAU03MACH]

Depending on how many miles are on it
I would pull the front cover off and inspect timing chains tensioner make sure all marks lighn up
That is something that really should be gone through once a purchase is done

 

[cobrajeff96]

Yes, the fuel pressure should go up even below WOT, should almost be linear. And what makes it that way is a vacuum source. When was the PCV valve replaced? Ever? Might be worth checking out.

 

[bobcat]

Yes, the fuel pressure should go up even below WOT, should almost be linear. And what makes it that way is a vacuum source. When was the PCV valve replaced? Ever? Might be worth checking out.

Thanks, definitely replace the pcv valve. Was looking at specs on new stock fuel pump and fuel pressure produced is 43psi so because mine holds 40 with the regulator un plugged I'm thinking it's not the pump

 

[Tillerman77]

I'm sure my issue has been addressed probably multiple times on this forum but after a brief search I found no definitive answers. I have a 96 cobra that aside from a cold air intake and cat back exhaust is stock as far as I know. I bought the car about a year ago from a stranger so it obviously has an unknown maintenance history. I purchased it to restore and fully expected to run I to some issues. Currently the car has a nagging skip issue under load howeveritruns well when I'm just tooling around in it and don'tkick it in the butt. I have preformed a full tune up which included new plugs, wires and filters. For peace of mind all fluids were drained and replaced. Skip remains. Replaced coils. Skip remains. Replaced fuel injectors with the stock 26lb blue top injectors which was what it had in it. Skip remains. Preformed a fuel pressure test and here's what I got. 30psi with ignition on and engine off. 35-38psi at idle and vacuum connected to regulator. Pressure goes down to around 28psi at wot (seems like it should go up). Dis- connect the vacuum from regulator and pressure holds at 40 psi regardless of throttle position. I'm an old school knuckle buster that's far more familiar with carburetors than fuel injection so any advice is appreciated. There is definitely a solid peace of mind from knowing first hand all the parts I've replaced but the irritation is real when I can't seem to rid my car of to demon. Thanks in advance for any help

At what RPM does the skip happen?

 

[bobcat]

Depending on how many miles are on it
I would pull the front cover off and inspect timing chains tensioner make sure all marks lighn up
That is something that really should be gone through once a purchase is done

Yeah haven't checked timing yet. Figured it runs pretty sweet when cruising that the timing wouldn't be the issue

 

[bobcat]

At what RPM does the skip happen?

Haven't really found a specific rpm but it definitely occurs when trying to pull hard

 

[RAU03MACH]

Usually I'll go through the whole motor and transmission after I have got it home then worry about the little stuff later

 

[Tillerman77]

Haven't really found a specific rpm but it definitely occurs when trying to pull hard

The reason I ask is that the IMRC switches at 3250 RPM. If you felt the skip or bog around that RPM, it could be the IMRC plates are sticking.
Do you have any MIL or engine codes?

 

[bobcat]

Usually I'll go through the whole motor and transmission after I have got it home then worry about the little stuff later

That's kinda my plan. Have too many projects going at once right now. I'm in the final stages of completing a full restoration on a 78 Nova that's occupying my garage. Been trying to focus on things I can do in the driveway like interior work. Got the Interior completed and rag top replaced. Just trying to get rid of skip now and will focus on more extensive work when I free up my garage

 

[RAU03MACH]

It possible tillerman is also on to something

 

[bobcat]

The reason I ask is that the IMRC switches at 3250 RPM. If you felt the skip or bog around that RPM, it could be the IMRC plates are sticking.
Do you have ant MIL or engine codes?.

Don't know what ant MIL is lol but no engine light. Haven't put a code reader on it. I though about the IMRC plates. I've read that I can tie them open to test but to expect to lose some low end torque. Is this true? Also I replaced the plugs with standard copper core autolights. They have less than 300 miles but wondering if these 4v motors are too much for standard copper cores. Just drawing at straws at this point

 

[RAU03MACH]

Mil is not on so that a good thing check engine light

 

[RAU03MACH]

If you tie the plates open you will lose a little on the low gain on the high

 

[RAU03MACH]

I'm running a regular motorcraft plugs nothing special

 

[bobcat]

Mil is not on so that a good thing check engine light

Lol so that's what a MIL is. Forgive my ignorance. I never heard a check engine light called that. My world is very small

 

[bobcat]

I'm running a regular motorcraft plugs nothing special

Cool. I said autolights but I meant Motorcraft. There again too many projects

 

[RAU03MACH]

If your learning thats good

 

[bobcat]

If you tie the plates open you will lose a little on the low gain on the high

Should rule out the plates being the culprit though if I tie them opening and still have skip

 

[RAU03MACH]

Dose not hurt to check for operation of those plates