95 Barely Running at This Point Misfire Codes (1 Viewer)

[702FZJ80]

145K.....Was running very strong and smooth with a long crank after warm up..........

Then I tried to fix the long crank and the truck is to the point where I can't even get it out of the garage now.

I've started a lot of threads trying to figure this out, so I apologize in advance for that. I'm going to compile everything here and hopefully get a solid lead to go on, I'm running out of ideas and not at the point where I'm ready to just start changing parts.

The truck fires up and idles low while stumbling, it doesn't have enough power to get itself down the road at all.

I've changed vacuum lines that were fitting loosely over their connections
new NGK v-power spark plugs as listed in the manual
new Fram fuel filter
carefully sanded contacts on fuel relay
cleaned MAF sensor with special cleaner
checked air intake boot for cracks
rebuilt stock charcoal canister with new charcoal and cleaned check valves

Things to note:

I'm not getting vacuum at the purge valve hose going to canister even at 3000rpm on a warm engine

Pressure still builds in the gas tank

black fuel and particles came out of filter when I blew it out with air

When I hit the muffler with a hammer I can hear debris in the bottom of it

There is a hissing sound coming from the vacuum port leading to the brake booster/EGR area. But when I spray starting fluid there it makes no difference in the idle.


The ground plug going from intake manifold to body ground and back to coil has been unplugged since I bought the truck, the morning I plugged it in, the truck started running as it does now. I checked voltage at the ground plug coming off of the intake manifold and it showed .20 volts with the plug unplugged, it showed 0 volts with the plug plugged in. Could I have burned the coil up by grounding it to .20 volts coming off the intake manifold? The plugs were separated from the PO and not taped up or anything.

I've gotten it running much better along this journey, and every time I disconnect the battery to clear the codes, it runs worse and worse.

First code was P0170
Next code was P0125
current codes: P0300, P0302, P0303, P0304, P0305, P0306


Any help would be greatly appreciated.

 

[nukegoat]

Do you have the fsm? Google for it and follow the testing procedures for the maf, iac, and tps. Look for air leaks since they will ruin the computers readings. Fix the leaky brake booster hose thing.

 

[nukegoat]

I also didn't know people rebuilt charcoal canisters

 

[ton504]

Find the hissing issue. Your problems makes me suspect a vacuum leak. Unmetered air will do all those things you mentioned.

 

[elhombre]

Take some needle nose pliers and squeeze off the brake booster line to check for the vacuum leak. Does the idle change??

All the grounding wires need to be plugged in.

 

[SUMMIT CRUISERS]

As others have mentioned, fix the known problems...hissing vacuum leaks. You might also look at purchasing a replacement charcoal cannister from Autozone. There are several threads about it.

 

[702FZJ80]

I downloaded the FSM and the first thing I came to in troubleshooting that I haven't done is check resistance in the coil.

Primary cold resistance should be between .36- .55
Secondary cold resistance should be between 9.0-15.4

my readings were within spec!


I hunted for the vacuum leak with cigar smoke last night and starting fluid earlier in the day. I unplugged lines and plugged them off with my finger and no change in idle. I'll keep hunting there though.......

 

[george_tlc]

Measuring <1 ohm resistance with a multimeter (are you using a) a decent meter and b) have you measured the actual lead resistance of your meter) is problematic.

You can't have 'fried' your coil, it is MEANT to have ground potential on the other side of the coil primary - so reconnecting a good ground path is not your problem, the problem is either whatever the PO was 'fixing' by disconnecting things or some other issue.

Your first step is to fix the identified issues - vacuum lines, hissing etc, before chasing ghosts...

If you disconnect the battery between tests, the ECU will reset back to factory defaults. Weird idle conditions are common until it relearns. It would be a much better plan to reset codes with the OBD2 scanner so you don't reset the ECU each time.

How long have you owned your 80 and how long before these issues cropped up?

cheers,
george.

 

[702FZJ80]

About a month

Measuring <1 ohm resistance with a multimeter (are you using a) a decent meter and b) have you measured the actual lead resistance of your meter) is problematic.

You can't have 'fried' your coil, it is MEANT to have ground potential on the other side of the coil primary - so reconnecting a good ground path is not your problem, the problem is either whatever the PO was 'fixing' by disconnecting things or some other issue.

Your first step is to fix the identified issues - vacuum lines, hissing etc, before chasing ghosts...

If you disconnect the battery between tests, the ECU will reset back to factory defaults. Weird idle conditions are common until it relearns. It would be a much better plan to reset codes with the OBD2 scanner so you don't reset the ECU each time.

How long have you owned your 80 and how long before these issues cropped up?

cheers,
george.

It's a cheap multi meter, my friend has a good one I'll try it and see what it says. I agree about the hissing.

I've had it about a month and a half and it's ran flawlessly until I tried to fix the high gas tank pressure and plugged in that ground plug. Then it all hit the fan!

 

[george_tlc]

Regardless of the meter 'quality', you need to DETERMINE the resistance of the meter's leads. Short the two leads together on the ohms range and note the reading. Deduct that from your other resistance measurements.

Check ALL the OEM grounds from the engine to the body/battery. There are several connections - match them up with the FSM and make sure they are all secure/reliable.

If you meddled with the canister (especially re-filling it) and other stuff - it may be possible you've dumped 'stuff' into the filter or into the injectors. Each injector has a mesh filter - so if those are now clogged with debris.... Hopefully that's not the case.

I'd revisit all the areas you touched since 'fixing' things

cheers,
george.

 

[702FZJ80]

The coil is within spec using 3 different meters and the shorting of the leads protocol. Thanks.....

Would a stuck egr cause this problem? The hissing is coming from that area.

 

[clownmidget]

check the EGR modulator. Several folks have discovered the bottom of it is melted, the plastic nipple is broken off, or the vacuum hose is cracked, etc.

 

[702FZJ80]

I checked the EGR modulator with the engine off per the FSM, seems to check OK, the filtering medium was very clean on top. I was able to blow through the port while blocking the other 2 with no restriction. (other than how tiny the hole is that the air was flowing through)

Now I've got the EGR off and it seems to be functioning when I suck air on the vaccum ports on top it moves the diaphragm up and down with little resistance.

There was no EGR gasket between the EGR and manifold, I wonder if that was part of the problem? Being that nobody in town has one, I'm going to use some copper sensor safe, high temp rtv nice and sparingly and mount it back up after dinner.

 

[702FZJ80]

Got the EGR reinstalled, letting the sealant dry overnight before re-firing it..........

I pulled the heat tape off of the wiring harness running by the EGR per another Mudder's suggestion and the wires were good as new under there. The heat tape was beginning to break down so I used some fresh stuff that looked like space suit material my buddy had. Wrapped it all back up and feels good to get a little PM in during this drawn out diagnostic affair.


My friend is bringing a scan tool with live data over tomorrow, should fix it. I'm guessing plugged exhaust or bad fuel pump at this point.

If just a sensor was bad, the truck would run in closed loop, and still be able to drive, this thing is not getting fuel or the exhaust is blocked, that's my only thing left at this point.

 

[Reelitchy]

I remember you making a few different post but seem to recall you cleaning the TB at one point. Possible you have the vacuum lines to the modulator swapped. ( on the TB or mod) Take the vacuum lines off modulator and plug temporarily then see if it runs

 

[702FZJ80]

Vacuum lines are ran correctly according to the diagram under the hood.

I'm getting 0 Ohms resistance between terminals 5 and 6 at the fuel pump harness per the fsm it says range should be .2-3.0

I'm getting 1.5 ohms reistance at the #3 port on the fuel relay when the other lead is grounded to the body.

The fuel pump is running when I jump 12 volts directly to the #3 ports.


WTF IS WRONG WITH THIS THING!

 

[Offroads4x4]

? Have you checked you air intake tube for cracks? You can test it by wrapping it with plastic wrap and then duct tape to see if you have a hair line crack.

My other guess was your wire harness by the EGR but it appears you've looked at that.

Cap, rotor, plugs and wires may be in order for a good tune up. If you wires are old and brittle sometime just bumping them will break the continuity capacity enough to make any rig misfire as well.

I realize none of these are related to your grounding issues but can give you the same type of problems you describe.

Just some thoughts.

 

[702FZJ80]

? Have you checked you air intake tube for cracks? You can test it by wrapping it with plastic wrap and then duct tape to see if you have a hair line crack.

My other guess was your wire harness by the EGR but it appears you've looked at that.

Cap, rotor, plugs and wires may be in order for a good tune up. If you wires are old and brittle sometime just bumping them will break the continuity capacity enough to make any rig misfire as well.

I realize none of these are related to your grounding issues but can give you the same type of problems you describe.

Just some thoughts.

I'll check the air intake again just to be sure, I like the plastic wrap idea, that sounds like my speed! haha

New plugs are in and the wires and cap/rotor are fairly new. I checked resistance of the 1 plug wire and coil wire per the FSM and they are within spec. The misfires are for all cylinders so it would have to be something central, not something running to an individual cylinder.

I'm going to check fuel pressure too.

 

[702FZJ80]

FIXED!

I checked the fuel pressure at the banjo bolt on the tank and was getting 20PSI at idle and it wouldn't go up when running the RPM's up. As soon as the key was shut off, the pressure dropped instantly.

The cause?

The pump itself worked itself out of the housing and was hanging crooked off the side of the housing and the hose was only about half way on. Letting most pressure blow by obviously. Put it all back together, bending the little mounting bracket at the bottom up a bit at the ends to hopefully hold it better. I was going to put a piece of stainless steel wire tie around the pump to the pump body but was worried about grounding the pump out so I didn't . If this problem happens again I'll probably buy a submersible fuel tank hose ($30 per foot at Napa) and line it with wire to keep from grounding out the pump and put it around the pump and secure it to the housing. For now, I think it will be great.

Thanks for everyone's insight and tips! I really got to know the truck along the way and have done plugs, fuel filter, new vacuum lines, rebuilt charcoal canister, cleaned out EGR, cleaned contacts on Fuel Relay and new tape around the wiring harness near the MAF etc etc etc. So lots of PM done anyway.

If your truck doesn't want to run, CHECK YOUR FUEL PRESSURE!

 

[Kernal]

Interesting find, was the rubber cushion at the bottom of the pump still in place, and could you tell if the fuel pump was the original or had it been replaced?