Please help me interpret this new info. So I decided to run a cylinder balance test and on the first run cylinders 7 and 6 came up weak. The second time through 5 6 7 and 8 came up weak. The third run all those plus cylinder 2 came up weak thats 5 out of 8. Compression is 115- 125 on all cylinders, plugs look good, injectors are brand new. I'm thinking harness, I'm going to go clean my salt and pepper shakers now. Any other ideas?
more weak cylinders than strong
- Thread starter fordnatic
- Start date
anybody else? Fact of the matter is this. I've got weak cylinders, they are causing the motor to lope. I dont know why they are weak, I'm trying to figure it out. The engine runs strong off idle but this lope is driving me crazy, sounds cool and all but I want to be running 100 %. Any help or ideas would be terrific, Thank you much.
Since all the compression readings are similar (you dont list your testing method, so absolute numbers dont mean much. But their relationship certainly does), I would be lookin for a reason for the lope/miss.
The cylinder balance test looks for an RPM drop as it cycles which injector is cut. The fact that it does not like what it is seeing suggests that the cylinders are missing to a degree. But I dont see a reason to believe that it is a hard-part fault. For instance, it could be an ignition issue (which will cause a cylinder or 5 to test bad in a CB test).
That was where I was going before. I know you were now looking for opinions from others, but I just wanted to clarify.
Were there any codes? When I mentioned different methods of testing compression: if, for instance, the motor was not hot when you did it, then the numbers can be low. Then things like having a charger on the battery, all plugs out, Throttle at WOT, etc all change readings. That was what I meant there.
I originally missed where you said that you were lookin for opinions on interpreting the data - my bad.
Good luck and bump for you for others.
The cylinder balance test looks for an RPM drop as it cycles which injector is cut. The fact that it does not like what it is seeing suggests that the cylinders are missing to a degree. But I dont see a reason to believe that it is a hard-part fault. For instance, it could be an ignition issue (which will cause a cylinder or 5 to test bad in a CB test).
That was where I was going before. I know you were now looking for opinions from others, but I just wanted to clarify.
Were there any codes? When I mentioned different methods of testing compression: if, for instance, the motor was not hot when you did it, then the numbers can be low. Then things like having a charger on the battery, all plugs out, Throttle at WOT, etc all change readings. That was what I meant there.
I originally missed where you said that you were lookin for opinions on interpreting the data - my bad.
Good luck and bump for you for others.
Well cleaning the 10 pins didn't help, but it didnt hurt either. I put my timing light on it and I notice its bouncing a bit... with the lope, when i throttle it up it advances and holds steady. Why would the timing bounce at idle? I've searched for vac leaks but have found none, doesnt mean they arent there but if they are i just cant find them.
txstang84
15 Year Member
you sure the lope you're talking about isn't a idle surge? I dont' see in your sig whether or not you have an aftermarket cam, so I'm assuming (wrong thing to do I know) you're still sporting the stock H.O. cam. There's several people on here that deal with or have dealt with that issue when installing bigger TBs, MAFs, injectors, intakes, etc.
if the idle is surging, then the computer will make decisions for timing based on all the parameters fed in from all the sensors (MAF, TPS, ECT, ACT, etc, etc, ad nauseam)-that would more than likely cause your timing to "jump" around at idle which will only worsen the idle quality. The only other thing I can think of is that possibly your dizzy is on the fritz.
if the idle is surging, then the computer will make decisions for timing based on all the parameters fed in from all the sensors (MAF, TPS, ECT, ACT, etc, etc, ad nauseam)-that would more than likely cause your timing to "jump" around at idle which will only worsen the idle quality. The only other thing I can think of is that possibly your dizzy is on the fritz.
txstang84
15 Year Member
just a little query on fault history here; when did it start doing this? Did you recently change/disconnect anything? Honestly 10psi variance isn't all that bad...thats about what I'm running...anywhere between 115-125.
txstang, the car has been doing this since I put this combo together, everything was disconnected at some point in the build. I do still have the stock cam, and I dont believe it is surge because it idles consistently at 750, it doesnt jump up or down it just lopes. Thanks for the input I truly appreciate it.
txstang84
15 Year Member
Heres the new situation, since cleaning the 10 pins all that comes up weak is 6 and 7... still. I checked to make sure there was spark to them, there is. I swapped plugs from one bank to the other as well as injectors to see if the problem moved with these components. The problem doesnt move, so I'm back to looking at the harness... oh yeah and I tested the injectors while I had them out, They all seem good and work fine in thier new holes. Any input?
Was the chunk of carbon very big? It should have kicked an EVP code.
Glad to hear you got it. leaking EGR does cause idle degredation, but I had not considered it a lope (must not have been too much inert gasses being introduced at idle).
nice work!
Glad to hear you got it. leaking EGR does cause idle degredation, but I had not considered it a lope (must not have been too much inert gasses being introduced at idle).
nice work!
Zero_chance
Founding Member
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