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Pinging under medium to heavy throttle


Natedog

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I've been having pinging (detonation or pre-ignition) since I got my 87 running with my m5r1 trans. It now has all the 1988 emissions parts on it including the eec unit (eliminates EGR and knock sensor) and it runs alot better but the pinging still occurs. Used the 1987 eec/engine wiring harness though. My pinging starts at about 3500rpm or a bit higher and mostly during medium to heavy throttle. It seemed worse this morning when it was colder (35*F).

Also my idle is kinda rough, plugs look good, and it sometimes does one little tiny backfire when I shift to second gear and accelerate at about 1500rpm....and also sometimes when I decelerate and then re-accelerate at low rpms in second gear.

EDIT: ALways ran 87 octane gas in my other 2.9 and now in this one. This engine was supposedly rebuilt by the previous owner and it looks and feels like it has. Last night I filled the tank with some 89 octane and it didnt' seem to help. Maybe they upped the compression too much and I need 92 octane fuel? I checked at fill up and I'm only getting about 14mpg or a bit less and that seems pretty low considering that I usually drive with light to medium throttle, not flooring it all the time.

What do you suggest?
 
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holyford86

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pull codes.
 

Natedog

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Just finished pulling codes and I got KOEO 95:

(O) Fuel pump: open, bad ground or always on - Power / Fuel Pump Circuits
(R) AIR not Diverting (AIRD) - Air Injection
(M) Possible bad fuel pump ground or open between fuel pump and pin 8 at PCM (Fuel Pump Monitor signal) - Power / Fuel Pump Circuits

and KOER 11: all ok.

WHile warming the engine up for KOER test holding the idle at 2200 for two minutes, I can hear a VERY SLIGHT surging (so slight that most people prolly wouldn't even notice) in the engine and also probably about every every ten to fifteen seconds (less frequently than the surging) the factory tachometer will jump up about 50 to 100rpm and then back down.

While checking timing it is fine with the spout removed...10 BTDC, but with the spout in the timing is at about 26 BTDC but jumps around from 27 all the way down to 19 occasionally but mostly between 27 and 228 BTDC....wtf? Seems a worn/stretched timing chain would jump around all the time not just with the spout in.

Also paying alot closer attention to the engine while driving and it is pinging above 4000rpm even at light throttle.

I've run several cans of fuel injector cleaner through it since I got it running about 700 miles ago and currently have a can of Berryman's B-12 fuel injector cleaner in the rear tank (the tank that I'm running on at the moment.) I'm doing all the injector cleaner as a precaution because the donor truck with the rebuilt engine had been sitting awhile and was not real well taken care of by the current owner.

Sprayed carburetor cleaner around the intake gasket and throttle body yesterday morning and had no change in engine idle.
 
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holyford86

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if youre getting a fuel pump circut open code check your fuel pressure. might have burned up the lift pump in the tank, which will eventually fry the frame rail pump.
 

Natedog

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Drove my truck at lunch today and it is doing the same thing on both fuel tanks. Doubt both in tank pumps would go bad at the same time although it would follow my luck lately. What about the main fule pump and/or the fuel pump relay? Will recheck my fuel pressure tonight....couple years since I checked it last and it was good then, but that's been awhile and prior to all this swap stuff I've done.
 
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MAKG

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Fuel pump circuit problems need not be with the fuel pumps themselves.

Look for voltage drops.
 

Natedog

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MAKG, Like voltage drops at the pumps in tank and on the frame rail?

The large square plug that comes from the wire harness going down the drivers' side frame rail (goes to all three fuel pumps, both tanks and the tail lights) has a black wire that is frayed and maybe half of the wires are broken. That could cause poor ground and/or voltage drop issues....not sure if it is black or black with a stripe have to look closer.

Where is a good place to get replacement pins for these plugs? I have a spare wire harness from donor truck, I guess I could solder in one of those leads no matter what color it is at least it has the correct plug on the end to go into the plug shell (plastic piece). These are some really crappy design plugs with the crimped ends all open to the elements. This may not be the only wire going bad at the plug down there.
 

Natedog

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Finally had a little time tonight and checked fuel pressure at the rail. It is 40psi with KOEO, 31psi running at idle and if I give it a little throttle it jumps to 35psi, alot of throttle and it jumps to 40psi. As the engine rpm catches up to the throttle position the fuel pressure drops down to 31psi.
 

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Checked the fuel pump voltage at the pump KOEO with DVM and it starts at 0 volts, jumps to 1.0 volt, then 10 volts, then the fuel pressure shuts off the power to the pump because it's fully pressurized. The pump runs for such a short time that my DVM auto-ranges and can't get the final voltage before the system pressurizes. So I used an old analog voltage meter to check it and it jumps to 10 volts and then the power shuts off.,..apparently the old analog meter has a damper on it and so it doesn't just jump right up immediately.

I did KOEO with the main pump un-plugged and listened for the in-tank pumps. The in-tank pumps ran and then shut off almost as fast as when the main pump was connected too! I did the front tank and then shut off the key, switched tanks, and then KOEO again and same quick system pressurization. Seems all good here.

Last night pulled the distributor and swapped it with my original disstributor (including TFI, pickup coil, cap/rotor and wires)....it doesn't ping anymore! The TFI had no heatsink grease on it and was hard and crusty where some kinda grease or whatever was in there and completely cooked out.

Cap and rotor were pretty crusty so I scraped them clean cause I didn't have a car to get to the parts store and it was late.

Re-set base tiimiing to 10* btdc with spout removed...all good! Plugged spout back in and still runs pretty good but timing mark intermittently kinda jumps around more than it should. Any ideas? I'm thinking the distributor shaft bushings are too worn. It has 0.025" endplay as measured with a feeler gauge at the base of the distributor. The shaft also has side to side play at the base (drive gear end) but top end seems pretty good. Is there a kit or specific bushings that I can buy to rebuild it?

Also have some slight exhaust leaks at the manifold to heads...could smell and hear it when I was down in the engine compartment re-setting the base timing. Guy who rebuilt the engine used gaskets on the exhaust manifolds. Do I need to do anything to them before I remove the gaskets?
 
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Natedog

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Running pretty good, but still need to figure out the spark scatter. Pinged a couple times yesterday but good otherwise.

ANybody?
 

richardl0565

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Nate gaskets do help a little if your manifolds are even slightly warped. If the guy that did the rebuild did not have the face milled than I would say if you take the gaskets off then have the manifolds milled to make them flat or use new gaskets your blow by will stop. If its leaking around the gaskets anywhere than you may have warped manifold(s). The spark knock may be a tooth off on the timing chain when the rebuild happened.
 

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Richard, thanks for the advice...need to check it out but gotta get my sspark scatter fixed first so I can pass smog referee. Replaced distributor with a rrebuilt and it has a good bit more power and is smoother. But, the spark scatter is STILL THERE! I heard the spout connector plug has a resistor in it and sometimes they go bad causing this problem? Ohmed it and it is 0.2ohms....pulled spare out of my spare harness and it ohmed same. Swapped it out just to see. Didn't have time to put a timing light on it and it's cold and pouring rain all night. Guess we'll see how it drives toomorrow. BTW, idle is a bit high now at about 1000 RPM.
 

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Bought a rebuilt distributor last week and installed it. Bushings in the new distributor definitely had less play in them than either of my used ones. Truck runs alot smoother and more power, but the timing spark scatter is still present!!!!

Pulled codes again tonight and I get the same codes as before!

...KOEO 95:

(O) Fuel pump: open, bad ground or always on - Power / Fuel Pump Circuits
(R) AIR not Diverting (AIRD) - Air Injection
(M) Possible bad fuel pump ground or open between fuel pump and pin 8 at PCM (Fuel Pump Monitor signal) - Power / Fuel Pump Circuits

and KOER 11: all ok....

...While checking timing it is fine with the spout removed...10 BTDC, but with the spout in the timing is at about 26 BTDC but jumps around from 27 all the way down to 19 occasionally but mostly between 27 and 228 BTDC....wtf?
While warming the engine up for KOER test holding the idle at 2200 for two minutes, the engine surges 100 rpm higher and then drops back down. I tried holding it at 2500 rpm, and 2800rpm and it still did the same thing....no pattern to the surging.

I'm just about done with this POS.,,gettin ready to cut my losses. Anybody have any suggestions as to what might be wrong?
 
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IMenriched

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Bought a rebuilt distributor last week and installed it. Bushings in the new distributor definitely had less play in them than either of my used ones. Truck runs alot smoother and more power, but the timing spark scatter is still present!!!!

Pulled codes again tonight and I get the same codes as before!



While warming the engine up for KOER test holding the idle at 2200 for two minutes, the engine surges 100 rpm higher and then drops back down. I tried holding it at 2500 rpm, and 2800rpm and it still did the same thing....no pattern to the surging.

I'm just about done with this POS.,,gettin ready to cut my losses. Anybody have any suggestions as to what might be wrong?
WEll...you have gone to the newer emission system to eliminate the EGR...correct?

I'm sure you feel you already have a flat spot on your forehead from beating on the wall....step back, reassess.

Just tossing a few thought out there.

how many miles on this unit? & since the "uprgade" of emissions systems?

that being true...this hints of a vacuum leak. did you just block off the EGR port with a plate or keep the old egr on?? recheck lines, check vacuum pressure.

Seems to me I was reading, here, maybe somewhere else, that someone else was having simular issues and found carbon blocking off a port in the upper intake.

have you had the alternator checked to see if it is putting out correct voltages/amps...thinking that the voltage regulator sending surges...extreme I know.

Is the O2 sensor the same for unit with a EGR (pre 88') as for those without, the EGR (88' and later)??

Have you done a compression check?

Hope that helps
 

Natedog

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Imenriched, yes already gone to the 88 emissions setup thereby eliminating the EGR.

Miles on which unit? about 1200 miles since I swapped the emisions parts.

Used the factory block off plate where the egr bolts on. Only used RTV and looks like it's leaking there as indicated by the oily residue gathering around this spot, so I bought a proper gasket today and will put it on tomorrow.

I agree that the only thing left to cause this would be a vacuum leak.

Could be some carbon in the upper intake blocking off a port, it was really gummy and black in there when I got the truck and sprayed carb cleaner in there while running to help clean it out.

Haven't checked alternator volt/amp output but it keeps the battery charged. It sounds like the bearings in it are shot though, going to swap it with my old rebuilt unit.

I think the O2 sensor is the same....IIRC I checkd at the autoparts store and they said same part number.

Haven't done compuression check...plugs all look great though and the motor feels tight.
 


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