Need help with spark knock
Thread Starter
|
Member
Joined: May 2022
Posts: 2
Likes: 0
From: tucson, az
Need help with spark knock
ok so my 94 4.0 ohv is spark knocking under load and i cant seem to find the problem, heres the "timeline".
i drove it for about a year and a half with no issues. then it started spark knocking, but i had no idea what that was at the time so i thought it was a transmission issue because it got worse the higher gear i was in which i now know had to do with the amount of load on the engine. i parked it for about 2 years and over the last 6 months have been driving it again and trying to solve the issue. the first thing i found was that the alternator pulley had rubbed a hole into the plastic intake tube. i plugged it with some rtv and tape and it fixed the spark knock for about two days. when the spark knock returned i did the upper and lower intake gaskets as well as the fuel rail gasket. this didnt completely fix the issue but lowered the intensity of the knock by about 50%. slowly the knock started to come back so the other day i finally bought a new intake kit and a new MAF sensor and changed them both out which, again, fixed the spark knock completely for about 3 days. i have also replaced the fuel pump recently as well.
the only other thing i can think of to easily change out is the two upstream O2 sensors on the exhaust manifolds. the truck has no EGR system that i can find and im not sure if it came like that from the factory or if the previous owner had deleted it and not told me when i bought it. it isnt throwing any codes.
some other information im not sure is relevant:
i drove it for about a year and a half with no issues. then it started spark knocking, but i had no idea what that was at the time so i thought it was a transmission issue because it got worse the higher gear i was in which i now know had to do with the amount of load on the engine. i parked it for about 2 years and over the last 6 months have been driving it again and trying to solve the issue. the first thing i found was that the alternator pulley had rubbed a hole into the plastic intake tube. i plugged it with some rtv and tape and it fixed the spark knock for about two days. when the spark knock returned i did the upper and lower intake gaskets as well as the fuel rail gasket. this didnt completely fix the issue but lowered the intensity of the knock by about 50%. slowly the knock started to come back so the other day i finally bought a new intake kit and a new MAF sensor and changed them both out which, again, fixed the spark knock completely for about 3 days. i have also replaced the fuel pump recently as well.
the only other thing i can think of to easily change out is the two upstream O2 sensors on the exhaust manifolds. the truck has no EGR system that i can find and im not sure if it came like that from the factory or if the previous owner had deleted it and not told me when i bought it. it isnt throwing any codes.
some other information im not sure is relevant:
- my gas gauge was showing past full basically the entire time ive owned the truck but after changing the fuel pump i had the pressure tested and they said my fuel pressure was a little low (cant remember the value) but said it could be due to the maf or the hole in the intake tube. since the pressure test the gas gauge all of a sudden started working again. no idea how that could happen.
- all spark plugs are white, so its running lean on all cylinders.
- engine doesnt spark knock untill it is warmed up, and only 4th gear and up, since i have changed out the intake and maf sensor. previously it would knock all the way up from second gear.
Welcome to the forum
Yes, change the O2 sensors, they are the only sensors that wear out, 100k miles or 12 years which ever comes first
And they are the ONLY feedback the computer has for air/fuel mix being correct
1994 4.0l Ranger only had EGR valve and Cam sensor if it was sold new in California, only state that required EGRs in that year, 1995 and up had EGR in all states
Put in Premium gasoline, 91 octane, as a test to see if the pinging is octane related, i.e. regular gas is 87 octane
Octane is a heat rating, lower octane will self ignite at a lower temp
If pinging goes away then you may have some carbon build up in the cylinders which has raised the compression ratio
Carbon also gets VERY HOT, so can ignite 87 octane early, so double whammy for carbon build up
But in any case run some seafoam in the gas tank to help clean injectors and break up some of the carbon build up
You will need to test fuel pressure again, 30-40psi is expected, but during the test raise RPMs to 2,000 and hold there, while watching pressure, if its slowly dropping then thats the problem, higher fuel demand is lowering pressure, but..........you should get CEL(Check engine light) and Lean Codes from O2 sensors if thats the case
After engine is warmed up and idling
Unplug the 2 wire connector on IAC Valve, RPMs should drop and engine may even stall, if so then No Vacuum leaks
If Idle doesn't drop then you do have a vacuum leak
If the 91 octane reduces pinging to 0 then you most likely
Yes, change the O2 sensors, they are the only sensors that wear out, 100k miles or 12 years which ever comes first
And they are the ONLY feedback the computer has for air/fuel mix being correct
1994 4.0l Ranger only had EGR valve and Cam sensor if it was sold new in California, only state that required EGRs in that year, 1995 and up had EGR in all states
Put in Premium gasoline, 91 octane, as a test to see if the pinging is octane related, i.e. regular gas is 87 octane
Octane is a heat rating, lower octane will self ignite at a lower temp
If pinging goes away then you may have some carbon build up in the cylinders which has raised the compression ratio
Carbon also gets VERY HOT, so can ignite 87 octane early, so double whammy for carbon build up
But in any case run some seafoam in the gas tank to help clean injectors and break up some of the carbon build up
You will need to test fuel pressure again, 30-40psi is expected, but during the test raise RPMs to 2,000 and hold there, while watching pressure, if its slowly dropping then thats the problem, higher fuel demand is lowering pressure, but..........you should get CEL(Check engine light) and Lean Codes from O2 sensors if thats the case
After engine is warmed up and idling
Unplug the 2 wire connector on IAC Valve, RPMs should drop and engine may even stall, if so then No Vacuum leaks
If Idle doesn't drop then you do have a vacuum leak
If the 91 octane reduces pinging to 0 then you most likely
Thread
Thread Starter
Forum
Replies
Last Post
