I think I either have a rod knock or a bad knock sensor. and maybe a few other things.

My 87 motor knocks only slightly on acceleration with the timing at 10*, but if you advance the timing to 16* it barely knocks at idle and knocks very noticably when you hit the throttle.

It has a phase two cam and 20k km's on a rebuild, 250k km's total, i put it together, machine shop did the bearings and stuff. The engine spun a few rod bearings originaly. I was told to set the timing an extra 4* advanced for the cam.

it idles erratically between 600 and 800 in drive, but usually stays at 600-650. but rarely and more frequently when i advance the timing, the idle dives slowly to 500 then to 450 then dies unless I tap the gas.

watching the timing with the advance wire togother, I can see the timing hit 30*to 40* when I throttle, and thats where I hear knock. I'm thinking the knock sensors not detecting a knock so the ecm is pushing it too far.

I had a full tank of gas, so i just added ocatane booster to it. it made no difference in sound, either did 20w50 oil. the oil guage used to max out when cold then dip down to 1/3 and hit 3/4 under acceleration, now it stays above 2/3. The old oil had 2000km on it and has just turning dark brown, the oil drain plug had 1/16" of metal filings on it and stiring a magnet on the bottom of the drain pan yeiled a few tiny flakes.

I'm not sure if i'm hearing detonation or bearing noise. it sounds faintly like the engine did when it spun bearings. could be that months of detonation wrecked the bearings?

If my engine is toast i would like to know what caused it.

what do you think? could a bad knock sensor cause the engine to behave like this? at $75 i want to make sure i really need one. I don't have an occiliscope to test it.

recent things i've replaced include fuel filter, vacuum lines, pcv, plugs, cap, rotor (wires, pick-up good), intake gaskets, valve springs, oxy sensor, used iac, tps, used maf, used tb (much tighter linkage).

fuel pressure has not been tested, because i have no way to do it, pump seems good because you can hear it prime well and the hose's shake.

I'm about to go out and change the egr to exhuast manifold gasket.

that reminds me, with timing adanced, you can hear EVERY exhuast leak and car spins it tire nicley. right now i can barely keep up to a new sufire.

educated guesses appreciated

later

 

First of all, I don't think we have Knock sensors on our cars. TomP pointed that out to me if I remember right. Second, 16* BTDC is WAY too much for our cars unless you're running 93 octane gas all the time. Detonation will KILL your motor. Basically what happens is that the pressure of the early ignition of the fuel tries to push the motor back on itself, plus the higher timing raises the combustion temperature, which reaises he tendency to detonate. I run about 13-14* in my car and can run 87 octane just fine...no knock, but if you were getting knock for a while before, most likly you messed something internally up.

Knock sensors started on the 3.1L motors I think, so you have to be careful when adding timing. Hope this helps you out a little.

Jeff

 

I was planning on setting the timing to 12 or 14 this time when after i find out whats making my car run rough. I have to find out how to test injectors and the maf, and i got my hands on an occiliscope so i'm gonna try to figuire that one out.


i'm having trouble understanding why my car is faster when it's detonating.

the knock sensor is on the back of the passenger head, and is one wire.

most cars at the junkyard today had three wires.

 

the one that's on the back of the head on our cars is the Coolant temp sensor, it has a green wire coming out of it. Our computer's aren't smart enought o handle the whole Idea of a knock sensor.

The car probly isn't faster when is detonating, just ffels like it because at the lower RPMs, there isn't enough timing to knock, so you do actually get more power and it makes it seem faster, but once you get above about 2500-3000 rpm, it doesn't pull as hard. I bet if you went to the track, it would prove the theory.

 

2_point8's right; that's the redundant fan switch you're looking at. Now Gen II frontwheeldrive 2.8's had knock sensors, that might've been the part # and price you were given. But those were DIS motors, ours aren't.

Also check your timing mark on the balancer. You might think you have 16 degrees advanced, but it might be 25! Make sure the mark lines up with zero on the timing tab when #1 is at TDC of the compression stroke.

When you set the timing an extra 4 degrees advanced for the cam, you didn't play with the valve timing, did you? IIRC a three way adjustable timing chain set allows for "straight up" valve timing, or 4 degrees advanced, or 4 degrees retarded.

And I do like 2_point's idea about why the car seems faster with advanced timing (lower rpm's okay, higher rpm's=slower). Know anyone with a Gtech that you can borrow? Hey speaking of that, I've had my gtech in it's box for the past two years. I should really take it out and see if it works...

 

I could be right about the it just seems faster thing. if I punch it at 30 mph it still presses me into my seat.

the harmonic balancer is good, i've had to get it to tdc a number of times so far, it shows 0* there. no special timing chain thing, thats an interesting concept though.


I plan to use premium gas next time and see if can advance the timing without knocking noise. I've been using a different gas station recently that may have low-quality gas, so that will change too.

but i still have a mysterious idle problem that sets no codes. I did get codes 43 (lean?) and 44 (rich?) before I changed the oxy sensor.

 

Bad gas and too far advanced timing was my problem.

I thought i try a full tank of localy produced gas, may have been sitting awhile. I only got 260km of a tank. but i did rev it alot.

knock is gone but throttle response is weaker. I set the timing to 12*, put 93 octane in it and changed the egr gasket that was disintegrated. Hopefully I didn't wear anything out by having the timing at 16*. I do tend to be hard on this thing. It hasn't stalled yet, but it droped to 500 rpm, at idle in park it stumbles evey 30 secs or so.

I noticed that when the car is cold it's much faster, more noticably than before.

I was planning on replacing the pushrods, springs, new valve guides(just cause i have an extra set), better rockers and covers. but now i wonder if its worth it.

but I will be looking into installing a v8 radiator.

thanks for the help

 

You put a cam in an aged high milage engine & expected it to last.
Those valve springs are the weakest point on the 2.8/3.1.
The 60* heads do wear valve guides rapidly.
Even my low milage 3.4 engine already has a worn valve guide (it was a 44K mile engine I installed, too).
The engine is aged and you are now experiencing the results.
Find a 3.4 for installing and enjoy those results.
The 3.4 heads have a dual spring design. You CANNNOT add dual springs to a 2.8/3.1 head. You'll hit water.
Serious, your engine is just aged beyond very good performance anymore.
You could also try changing to a colder range plug, too.
Add more fresh air coming into yur engine, that will also help.