Those are low readings.

 

OP, can you verify that you were getting back fires at the intake or are you getting popping/detonation a fuel in the catalytic converter underneath the car?

 

At the intake.

 

Yes, have been checking on that. So I guess I need to check my fuel pump.

 

If not the fuel pump how old are the o2?

 

So I pulled out the fuel pump. The strainer was all torn up and the fuel pump is for sure aftermarket as it has no longer the original connector. The fuel pump has some number marking, but they don't make sense to me. Just to be sure I picked up a new delphi fuel pump and strainer.
Keep you posted.

 

isnt the only way to get a backfire out the intake by having timing off so bad, or holes in the valves, so that the intake vale is open when e spark goes off?

did u use a piston shop to verify the timing mark is right and did u do a compression test?

timing chain skip?

the fuel gauge readings do appear low but how does that create backfire?

 

Compression reading are in the first post.
I've checked timing multiple times and I played with the timing either way. It only gets worse with significantly more or less timing.

Timing chain is still under consideration, but doesn't explain why there is no backfire during slight increasing the throttle to wot.

Fuel pressure is now an issue I found along the way. Have read it multiple times that a lean running engine can create that intake backfire. Try to fix everything as I go.

 

Sounds good. If that is the case with lean operation the. id say u have a very strong chance if being fully operational after the fuel pump repair. Look fwd to hearing results, im not a mechanic so the lean pop is something new to me.

 

If the timing is retarded it will run very lazy and can get to the point of manifolds glowing orange. If the timing chain skipped it would have problems at all speeds all the time so doubtful. There are few fuel pumps that can not supply enough for idle and 3000 rpm in neutral as only 10 hp to drive accessories and internal friction. Bad valve all speeds it is just as bad as one or any other it would also show up in compression test so and easter eeg hunt idea.

Cap rotor wires reluctor pick up coil or ICM are all possible they will show up as a miss dropping a cylinder or could backfire through the exhaust. Plugged injectors will cause a dropped cylinder miss or could backfire through the intake.

A bad cam or valve spring / valve gear can backfire out of either end. If it were me I would pull the valve covers and carefully check for broken springs a badly fatigued one can as well and not be broken yet. Rockers pushrods will cause a backfire as will a cam with a bad lobe.

If it continually backfires and seems to be the same one or two cylinders I would run it at a speed it backfires regularly and unplug one injector at a time to kill the cylinder and see it backfires less or stops backfiring. I would check under the valve covers first before I broke something big like dropping or bending a valve.

 

whew! I am not the OP but I would like to thank you for the education.

A bad cam or valve spring / valve gear can backfire out of either end. If it were me I would pull the valve covers and carefully check for broken springs a badly fatigued one can as well and not be broken yet. Rockers pushrods will cause a backfire as will a cam with a bad lobe

^^^ this stuff here, doesn this all relate to the valves being slightly open which allows the "firing" to escape back through the intake or the exhaust depending on which side its on right? just trying to ensure i understand. if a rocker arm is not pushing hard enough on the rocker arm, or the rocker arm is loose, would that potentially create a situation where the valve does not close all the way? or would it be more like not opening all the valve all the way? not sure what the effect of not opening valves all the way would be.

anyway, love learning this stuff its like brain candy for me. VT.

 

I have built and wrenched race engines for over 40 years and worked on electronics systems 20. The owners and crew chiefs always point at something very complicated when there is a problem and always turns out to be auto shop 101

 

Some good and bad news:
The good news is that the fuel pressure is up significantly.
Without vacuum is at 39 psi, but with vacuum it runs at 34psi.
When coming on the throttle there is no more hesitation, but I guess that is a consequence of below issue.

Unfortunately the backfire is still there and now the idle is way up ( 1200 rpm )

 

ddahlgren, Thank you! I will try to get the idle back down and then I will go on with these tests.
Cap rotor wires reluctor pick up coil and ICM all have been replaced already.

The problem is it doesn't backfire at a specific speed, it only does that when there is a sudden increase in throttle.
When slowly increasing throttle, it doesn't backfire.

 

What I have not heard clearly stated is what end does it backfire from and what it sounds like. Is it rhythmic or random? With a high idle and hesitation I would be suspect of the TPS or connections. A scanner to check what the ECM sees might tell a lot even if you use the loaner in a Autozone parking lot. Look for wrong voltage or dead spots in the travel that don't change with movement or just wildly wrong.

 

Another update. Since the idle screw was still sealed, I left it like that and focused on the TPS. TPS readings were a little high, after adjustment it now reads 0.54V. Also verified that at WOT TPS reads 4.4V. This confirms that TPS is working correctly.
After repairing a vacuum leak as well and re-adjusting the timing, idle is now at 660rpm. I don't think it was ever this low since I got the car.
Unfortunately backfire through intake is still there and now I can also hear a clear ticking sound at the passenger cylinder bank. Guess I need to pull valve cover.

 

It has been stated before it's through the intake. It's just a popping sound. The hesitation is gone since the new fuel pump, high idle is now solved with adjusting the TPS.

 

Well sounds like one by one the problems going away! That is good and down to 1 by the sound of things. You might pull injector connectors to see if valve gear or an injector making a racket.

 

Took a small recording of cranking it without the valve cover.
Fuel pump and coil were disconnected. Looks like the clicking comes from cil #4. Any thoughts?

 

Assuming an '85 uses a MAF and never worked on one is this one that unplugging it can uncover faults in it? Wondering if it does not see the accel and does not add enough fuel causing a lean spot and yes I am hearing hoof beats and thinking zebra but options running out.