'91 Ranger severely knocking after a tuneup

E

EPHhead83

New Member
Hi, I'm on this forum as of today to check out if anyone might have a suggestion for this situation - Any advice or knowledge shared is appreciated.


Noticed some hesitation duiring idling, and replaced the plugs, wires, cap, and rotor. The next day it began knocking violently - really sounded similar to a top-fuel getting ready to race (low RPM and pinging like crazy). Checked the plugs, firing order, replaced the plugs and wires with another set, but it's still happening. To note, the plugs I took out initially were burnt white - I am aware this means the engine is running hot, and replaced them (from Bosch Platinum to Bosch Platinum 2), but what caused such a drastic change in performance? Again any constructive response is appreciated.

'91 Ranger 3.0L 134k mi.
 
I had an issue similar to this a few years ago. You say the plugs were burnt white, that does mean it is running hot, but also means that you aren't getting enough fuel. A very lean mixture will cause the plugs to be white. You might check to see if the fuel pump is working... Turn the key to the "on" position and listen near the gas tank for the pump to prime... it should run for a second and then shut off. When this happened to me it was not that the pump was broken-- it still worked, but it had a hole in the diaphragm that wouldn't allow it to pump enough fuel. Regardless, if the plugs you took out were white, you almost definitely have an issue with not getting enough fuel. Putting new plugs in probably gave you hotter spark, and since it was already running hot due to lack of fuel, the issue probably is compounded and now the mixture detonates before it should.
 
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Bad Distributor

Thanks for the info - Checked the fuel pump; the priming stage sounded okay. Turned out what I said was knocking was actually misfiring, and the distributor was the cause.

After going through three different sets of spark plugs and wires, I have a bit of inventory lefttover - if anyone wants to buy/trade for it, they're available and intact:

1 set of 8mm wires
6 Bosch Platinum +2 plugs
6 Autolite standard plugs
 
Distributor itself

The new cap was fine - the rotor 'tab' was out of center and grinding away the contact points on the cap. After changing them both, the car still ran improperly and misfired. A mechanic changed the coil and distributor and it's running, but not as smoothly as before I tuned it - sounds like it's still misfiring occasionally.
 
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