Hey guys, I'm at a loss here with an issue we have been chasing down since buying this project truck.
1996 Discovery 180k on the clock
I have tried searching through the forums and there is alot on D2s misfiring but not as much on D1s and nothing that seems close to our scenario.
The guy who owned our truck was a bit of a hack, anything he tried to "fix" ended up being half done at best. So, we have spent the last month and a half trying to sort out the mess.
The main problem we have had since getting it running (needed a fuel pump in the first place) is a random misfire scenario and hard start combination.
When we first got it running up and down the street it didn't have much power but had no check engine light. It would bog down under acceleration and try to backfire sometimes. We originally attributed this to the idea that he was most likely using regular unleaded (87 ocatane). We first did a set of spark plugs (copper NGK) and that seemed to improve the situation a bit. The guy had the old plugs not really set at any specific gap, some were the correct gap, some were WAY off.
Once it became street legal and began driving it around town, fresh 91 octane helped quite a bit. There was no bogging down under acceleration anymore.
Then the CEL and misfiring began. Codes p1313 and p1314 off and on. The misfires are totally random though, some days it doesn't do it and the CEL isn't on. Some days the code is P1314, some days its both 1313 and 1314. Some days its nothing.
Then we replaced the wires with a cheap set from Autozone (All we could get for a temporary fix) The wires helped a little too, it seemed to misfire less often and more power returned.
Today we bought a new set of coils and dropped them in, more improvement in power but the codes still came up. We reset them and will see how long it takes for one or both of them to pop back up or maybe not. The hard start is still an issue.
They ONLY seem to pop up at speeds under 40, there is no misfiring on at higher speeds or when on the highway.
It has a newer radiator and correct 180 degree thermostat. The injectors are a working set off of my truck because I upgraded to the Ford injectors. We have done a Seafoam treatment which helped a little too.
If the cats were toast, wouldn't there be O2 sensor codes being thrown from exhaust values not being in check?
When shes running right, she runs like a top! But this random misfire is about to drive me to drinking.
Thank you for your time

 

Random misfires both cat A and B damage means it's over fueling when the codes pop. Check the Fuel Pressure Regulator - drivers side, end of fuel rail. Simple check is look at the vacuum line, make sure it's not split, checked, or off the diaphragm. Second thing is a vacuum check with a vacuum tool, make sure the diaphragm isn't perforated, holds vacuum.

At idle, high vacuum, the FPR is fully open allowing excess fuel through the rail back to the tank. At higher engine speeds it's closing or closed, low vacuum. If it's closing too soon it will force all the fuel to exit through the injectors. Engine off, no vacuum, it's fully closed/seated. If it's perforated it'll stay closed all the time.

Check the PCV noodle in the passenger side valve cover, make sure it isn't blocked and vacuum lines are good from it. Tighten the intake manifold bolts, 35 ft/lbs which is not a whole lot. Your checking for vacuum leaks, that'll make a Rover motor run like snot on a cold day.

If it still has cats and they're original they're probably toast. They may cause back pressure and that can prevent the air/fuel charge in the cylinder from fully combusting sending the excess towards the cats which in turn overheat and become molten. Rattling cats are chunked, hit them with a rubber mallet enough to hear if they'll rattle or you can also hear them with engine running..... Coolant in the exhaust is another way to destroy cats, don't like to hear stories of white smoke for days/weeks.

I suggest this to everyone but the upper most O2's you should replace if you have no history of if or when they where last done. They're your Engines sniffers and through them the engine's air fuel ratio is determined.

Consider a UG (in my sig) to get info on running conditions unless you have a scanner that can view live data. Helps to know what's what.

Just some random things to look at and keep you busy for awhile.......

 

Thanks for the response Ihscouts! That's a good bit of information to work on.
We did get a chance to check the fuel pressure regulator and it seems to be holding currently. I dont have a mighty vac to test it with yet but I may be able to scrounge something up in the next few days. I gave my friend the ultragauge from my truck so he can ride around with it for the next few days. I need to get down under the truck and bang around on the cats to see if they are rattling too.
The two downstream O2 sensors are the same value as the upstream ones according to the UG. I'm not sure if that is good but the only thing off is the passenger O2 value. That seems to float around under acceleration. Does that mean that its toast? We are going to try to get two new front O2s when the funds come in soon. For now the CEL has gone off after we pulled and cleaned the spark plugs after this coil change, they were pretty fouled up.

 

I don't know if you have the same issue as I did, but I think my spark plug wires were arcing either to each other or to the grounded engine block. I took the time to route them properly (using the clips on the rocker covers and making sure the lengths for each run is in order - shortest wire to shortest run, etc...) and my mis-firing is now completely gone.

 

I have tried to route the wires as best as I can to keep them from touching, even using some clips I purchased from the parts store. I dont think that is the problem but its always a possibility.
Well we figured out the hard starting issue. When we replaced the fuel pump, apparently one of the hose clamps didnt get tightened down all the way so the supply line was bleeding off pressure back into the tank. Once tightened back up, the truck starts first try, every time.
The misfire is still there though