98 7.4 L spark knock and power loss problem


IMAKEHP
06-13-2007, 02:52 PM
This problem developed 2 weeks ago. It seems to drive ok at lower speeds, but when you try to accelerate it spark knocks and or stumbles.

This is what I have done with no success.

New fuel pump
new fuel regulator
new fuel filter
new spark plugs
new dist. cap
Added Sea Foam
Checked ECM trouble codes/ no active codes

There was a low crankshaft duty cycle code in the history.


Any ideas?

67chevypickup
06-13-2007, 03:39 PM
well i have two possibilities in mind either the ignition control module in the distributor is bad or you have an ignition coil thats about ready to die. And ihave a question does it smell like its running real lean at idle or smoke?

777stickman
06-13-2007, 06:09 PM
Wow man, you spent a lot of time and money and it didn't fix it? That's what scanners are for, to check DTC's and troubleshoot. The days of throwing parts at a problem in hopes of fixing it are long gone.

Post the history DTC number so we don't have to spend time looking for the description you gave.

IMAKEHP
06-14-2007, 07:06 AM
Wow man, you spent a lot of time and money and it didn't fix it? That's what scanners are for, to check DTC's and troubleshoot. The days of throwing parts at a problem in hopes of fixing it are long gone.

Post the history DTC number so we don't have to spend time looking for the description you gave.

WOW YOU NEED TO CHECK YOURSELF!


THERE IS NO CODES!

That is what you have to love about the Internet, you go on to a web site looking for help and right of the bat you must be an idiot. The reason the fuel system was gone through was the fuel pressure was at the low end of specification.


And I repeat for the Internet genius, THERE IS NO ERROR CODES.

777stickman
06-14-2007, 09:19 AM
There was a low crankshaft duty cycle code in the history.




You might try PSUYA. Let us know if that helps.

777stickman
06-14-2007, 05:38 PM
Just for public record "IMAKEHP" sent me a PM saying "Do not post on this thread anymore. This is your only warning".

Now to the more serious stuff. I looked up your history code (PO337) CKP Circuit Low Duty Cycle. I really doubt that this has anything to do with your current problem. But?? If that code was set 2 times in a row it should have turned on the MIL. Since it was in history it may have been a random thing. But if it comes back it points to the reluctor wheel, wiring or excessive crankshaft end play, or CKP sensor problems.

As to your current problem. I would suspect some kind of vacuum leak some where. Have you pulled the plugs and looked at them for a really lean reading?

Hope this helps..........

IMAKEHP
06-15-2007, 10:32 AM
Attitudes
Note to Steve: Yes YOU do have an ATTITUDE THAT NEEDS TO BE ADJUSTED and You where warned. To which you did not take my advice.

Since you want everything to be as you say "public record"

Got your PM. I posted any way with what I hope will help you. You listed a bunch of stuff you changed that appeared to be related to your current problem. We're not mind readers and yeh I kind of cooped an attitude. It happens sometimes. So lets try to work thru the B/S and solve your problem as best we can. I've got the same motor and year as you in my Sub and the factory manuals for it. I'm too old to worry about threats but not too old to try and help.

I did post your threat for record but's lets move beyond that and try to fix your problem. By the way did you figure out the PSUYA thing?? It was another of those attitude responses.




Now back to the advice I was seeking. My initial fuel pressure readings where as follows.

Key on, pump running 58-60 PSI (old pump and new pump)

key on, as soon as pump shuts off after 2 sec cycle 50 PSI (old pump and new pump) this is why I changed the first pump

key on, pump on, engine running at idle 50 psi (old pump and new pump)

5 min fuel psi leak down test is 2 psi, 10 min. is 4 psi.

fuel return line closed, key on, pump on, 80 psi (new pump) This test damaged the fuel pressure regulator.

Does this look normal? I don't think my 98 Yukon has that much fuel pressure drop when the fuel pump cycles off. But then again it is a different type of fuel injection system. All spark plugs look as new. The only DTC codes that have been in the history are P0337 cleared that then a got an P0339. They are not active just in the history. Also note that this truck has 22,000 miles on it. And another symptom is it will only travel 62 MPH down they highway without dropping in and out of torque convertor lock up. If you try to accelerate threw this it spark knocks.

Things that have been checked are as follows:

Crank sensor, voltage in 12.2 vdc/ 4.75 to 5 ac volts output with engine running

MAP sensor voltage in and out

TPS voltage in and out

knock sensor resistance and acv out

Dist. gear back lash



Thanks for your help.

MT-2500
06-15-2007, 10:50 AM
EGR Valve?
Is it working good?
If not check it out. It can cause a spark knock.

What is the camshaft retard setting?

And as Stickman777 said.
Wow man, you spent a lot of time and money and it didn't fix it? That's what scanners are for, to check DTC's and troubleshoot. The days of throwing parts at a problem in hopes of fixing it are long gone.

Post the history DTC number so we don't have to spend time looking for the description you gave.

IMAKEHP
06-15-2007, 11:20 AM
EGR Valve?
Is it working good?
If not check it out. It can cause a spark knock.

What is the camshaft retard setting?

And as Stickman777 said.
Wow man, you spent a lot of time and money and it didn't fix it? That's what scanners are for, to check DTC's and troubleshoot. The days of throwing parts at a problem in hopes of fixing it are long gone.

Post the history DTC number so we don't have to spend time looking for the description you gave.

The first thing done to this truck was, to hook the scanner up to it to retrieve error codes. I don't understand Steve saying this or you quoting
it. Please help me understand.

The EGR valve moves freely. What other checks should be done?

Camshaft retard was in the range of +or- 2 deg (I don't remember exactly what the value was)

Thanks

MT-2500
06-15-2007, 11:53 AM
This info was not given in your first post.
The first thing done to this truck was, to hook the scanner up to it to retrieve error codes. I don't understand Steve saying this or you quoting
it. Please help me understand.

{His answer was based on the info given in your post.}

Now that we have more info and that out of the road we can better help.

The codes even if only history or stored codes are point to a crankshaft sensor or wiring to it problem.

Spark knock problems can be lean fuel mix or egr valve problems.
Make sure the egr valve is working and flowing exhaust gas back into intake.
A lot of scanners have a test for egr valve operation.

Check fuel trims for lean fuel.
Maf sensor reading right.
Baro readings right?
Tempt sensors reading good?
Are you using a after market air filter setup ?

IMAKEHP
06-15-2007, 12:11 PM
Check fuel trims for lean fuel.
Maf sensor reading right.
Baro readings right?
Tempt sensors reading good?
Are you using a after market air filter setup ?



I am using a K&N air filter. Cleaned MAF and drive tested same results. Then I installed the MAF sensor with temp sensor and paper filter from my 98 yukon, same problem.

Water temp on scanner was 199 deg.

Baro readings I don't know? Where would this be checked?

I will check the fuel trim. Does the fuel pressure look normal to you? Manual states 56-62 PSI. Is that when the key is first cycled?

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