2.4 CIS missing under load.

rching · 08-23-2010, 10:53 AM

My 2.4 CIS started to bog or miss when I try to accelerate quickly. Starts fine and runs good until I try and floor it. Changed plugs so far and will go down the list until I find the problem. Any suggestions? It has a Permatune instead of Bosch CD. Cap and rotor are clean, points not pitted and look good. Can it be the rotor and some kind of advancement of the ignition it it? Fuel filter? TIA

kodioneill · kodioneill's Garage

My 2.7 CIS bucked under load and I found it to be the injectors. I would check the pressures and check for fuel contamination then pull the injectors, with the hoses connected set them in containers and lift the distributor sensor plate with the fuel pump running and check the flow pattern and delivery rate.

ossiblue · 08-24-2010, 06:29 AM

My suggestion is to complete the ignition check first (since you've already started doing so), including the timing advance, then proceed to fuel. From your post, it sounds like this has just started to happen. Follow kodioneill's advice and begin with a check of fuel pressures, then fuel delivery--volume and pattern. It certainly could be a clogged filter or possibly, the fuel pump is dying. The fuel checks mentioned should point you in the right direction.

rching · 08-24-2010, 06:47 AM

Great direction to follow. I'll do the checks 1 at a time until I find the problem. Ossiblue, tell me if you ever go to Cars and Coffee in Irvine with your 73.5! I'm 10 minutes from there! Thanks for the suggestions!

prebordao · 08-24-2010, 06:48 AM

Apparently, I have the same symptoms on my 2.7, changed injectors, checked WUR but so far nothing.
Next I'll check advance curve and pump delivery.

PS - the new injectors did improve the top end as the old ones had a bad spray pattern, but did nothing to the bucking issue.

rching · 08-25-2010, 07:11 PM

I had some time this afternoon so, with the weather being 90+ degrees outside, I worked on the 911 in the garage where it was probably 100. Checked the gap on the points, around .015 then took the permatune out and put in a good Bosch CD. Fired right up, as usual and I went for a quick drive. At about 3K RPM is when it starts to miss under acceleration load. I can accelerate slowly and it will run fine. Any gear I'm in will miss when I step on it. Guess I'll follow my suggestion list and start on the fuel system, fuel filter, fuel pressure, injectors etc, I'll find it one way or the other and post the problem maker!

prebordao · 08-26-2010, 03:42 AM

do you also have the same miss higher up, like at 4k, 5k ?

Sunroof · 08-26-2010, 04:15 AM

Fuel filter first then road test...............
Any cracks in the rotor or distributor cap? Do you have the limited rev rotor? How old are the ignition wires?
I had the same problem years ago, changed out a crapload of CIS components and ended up with new ignition wires that solved the problem. Same holds true for the fuel filter. The CIS needs clean fuel and if your tank is original and never refurbished you know junk is going into the filter. I change mine every 6K just as cheap insurance although I refurbished my tank and lines last year. Take your time.........you'll find it.

Bob
73.5T/CIS

rching · 08-26-2010, 06:56 AM

The engine bogs down and misses all thru the RPM range from 3K when I'm on it. If I accelerate slowly, it revs up fine. But who can drive around like a little old lady all the time. Fuel filter is next on my list since I have that and it's been on my to do list. Cap and rotor are fine, I do have that rev limiting rotor though. Is that problematic? I may have the the fuel pressure checked over the weekend after I change the fuel filter.

ossiblue · 08-26-2010, 07:34 AM

Randy,

Sounds like you're on the planned path. One note though: if the filter doesn't clear things up and you have a pressure check done, that may not be conclusive. It's possible for the pump to provide static pressure but fail during actual driving due to lack of volume, so be prepared to perform a volume/delivery test regardless of the pressure readings. Further, a reading of amperage draw can indicate a failing pump as well.

BTW, I haven't gone to a Cars and Coffee as yet and my engine is currently having a top end done--hopefully all together in a couple more weeks.

h.wong · 08-26-2010, 08:39 AM

cars and coffee this saturday is the porsche marque i heaord...

ossi blue... where did you send your heads to ...and how much $$?

TIA
harry

Sunroof · 08-26-2010, 08:57 AM

Randy,
The reason I mentioned the rev. limiter rotor is because their is a black hard insulation type substance that seals the metal contact for the distributor cap contacts. I noticed mine had a deep crack in it from heat, age and that dreaded over revving. I did replace it and the car ran smoother. The problem however, did not cause the same issues you are currently having. I do not know how many CIS components you have replaced since you got the car, but over time I have had to pretty much change out everything from a cracked airbox to the cold start valve. Recently I had a fuel pump and ignition coil failure which was an interesting experience. When the CIS on the 2.4 works everything seems to be wonderful, otherwise it becomes a chase game. With these old cars it could be anything! Lets hope its as simple as the fuel filter.
I do want to recommend a cheap fix here that could help...............try pouring in a can of Seafoam or Chevron Techron in the fuel tank. Both are both strong solvents that will clean your injectors. Could not hurt.

Bob
73.5T

rching · 08-26-2010, 09:25 AM

Thanks Bob,
I was thinking of the Redline St-1. Or do you think they are all the same.
My car as 97K miles on it and I'm the 2nd owner. The CIS on it has been running perfectly until just recently. I'm sure I'll find it and the good thing is that it's getting me off my butt and doing maintainence stuff at the same time. I have been thinking of changing the cap, rotor and points but they are all excellent looking and I will consider doing that at a later time when I start running out of options. Maybe a 3.2L and forget about it! What do you think Harry?

h.wong · 08-26-2010, 09:28 AM

you finally figured it out...!!!!!!!!! i have the perfect car for you.......

rching · 08-26-2010, 09:35 AM

Is that all you do at work? Look for threads that I'm on so you can highjack them?
I checked the points yesterday and installed your Bosch CD. Same problem! I do have a call into Dennis to check my fuel pressure. I may be up on saturday with the 73.5' so look out. I'm stopping by your place to get some free work done!

Hope Bob isn't reading this because he'll know that I can go south to Capistrano and get free work from him too!!! : ) ( just kidding Bob) since you don't know me, the jokster!
Randy

rching · 08-26-2010, 09:38 AM

Oops, L.J. is in Capistrano! Don't know where Bob is! Must be our age cuz' he knows what a moon pie and RC cola are!

h.wong · 08-26-2010, 09:51 AM

maybe... i will meet you at cars and coffee irvine.......bring me a moon pie and rc cola...
haven't had it in over 40+ years.........

rching · 08-26-2010, 09:59 AM

Ha ha ! Well, I'm off for the rest of the day! Next week the Dental School is back to normal so I'm going to take advantage of the slowness this week and..... Look for the fuel filter I bought some time ago. Also stop by the dealer to see if they can get me the "pipline'' so i can connect the filter to the fuel accumulator like they did on the 74's. Call my cell if you need me!

h.wong · 08-26-2010, 10:02 AM

ok...i figured you are goofing off...a usual... wish i had a job like that..!!!!!!!!!

RC cola and moon pie......damn....you got the life....

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by rching

My 2.4 CIS started to bog or miss when I try to accelerate quickly. Starts fine and runs good until I try and floor it. Changed plugs so far and will go down the list until I find the problem. Any suggestions? It has a Permatune instead of Bosch CD. Cap and rotor are clean, points not pitted and look good. Can it be the rotor and some kind of advancement of the ignition it it? Fuel filter? TIA

Randy,

Replacing the fuel filter is an easy and cheap course of action. But is the filter causing you the problem? If you want to know whether the fuel filter is the culprit, simply hook up a pressure gauge and check your control and system pressures (3 times). Actually you just need to know your system pressure. I don't remember the exact system pressure for 2.4 liter (maybe 68-70 psi???) or refer to spec table.

Once you determined that your system pressure is OK, the fuel filter and FP are not the culprits and causing you the problem. Of course you could do further detail tests of the FP and FF if you desire. Now, you could focus on the ignition system including spark plugs and wires. Does this problem occur even when engine is cold? Or temperature related? Have you observed the engine running in total darkness? Keep us posted.

Tony