1997 D1 with 190k miles. PO did head gasket at 150k.
Currently missing, can feel engine shake in bay at lower RPMs and the exhaust has typical missing chug chug sound. Car is throwing P0300, P0305 and P1316. Occasionally on a cold start ill get the red service engine light on startup for a second or so (about as long as the oil light). Power/performance is still fairly decent so it doesnt feel like im down a cylinder at speed. No exhaust in the coolant or coolant in the exhaust. Typical oil leaks so of course some oil is being lost, exhaust doesnt feel excessively oily/black so I dont think its burning it. Idle is consistent and strong. Not losing any coolant.

Ive done

• New wires
• New plugs
• New coils (all)
• New injectors
• New cats+y pipe
• New MAF
• New O2s all around
• New IAC
• Reset adaptive values
• 15w-40 rotella
• Resealed plenum
• Fuel filter
• Seafoam/BG44k
• Checked fuel rail pressure
• Checked for injector leaks
• Bunch of other unrelated parts/checks

At this point im running out of ideas to check on. Anyone have any input/tests?
Motor mounts are good and tight+not rotted out so the shake isnt a part of that.

 

The attached file has details of the precise meanings of the codes and what triggers them. The file is also in the google drive in my sig with a bunch of other documentation and manuals.

Excess Emissions Misfire Fault - P1316
Random / Multiple Misfire - P0300
Misfire Detected - Cylinder 5 - P0305

You've done most of it. Have you replaced the cam position or the crank position sensor?

What plugs are you running?
What wires?

 

Ive been using an iCarSoft i930 to pull the codes and the internal DB lines up perfectly with those attached codes so that looks good to me.
I havent done Cam position or crank position, can those contribute to miss conditions? My understanding is that the crank position failure condition is sort of "works" or "dead car wont start".
Plugs are Denso 5305 Iridium
Wires are magnecor 8mm, but Ive also used a set of napa premium wires with no change.

 

Here are some ideas, for what it's worth. Maybe focus attention on cyl 5. Check plug gap and clean the sealing surface. Check compression (all cylinders). Check #5 wire ohms, clean ends, move to different cylinder to see if code follows. Coil should be good since it's twin cylinder is not misfiring, though corrosion can build up inside the coil HV connections. Maybe check timing with a light. Check base idle, make sure throttle and passages are all clean. Ensure crankcase ventilation is all in order.

 

98' Disco so we have the same beast. My PO had a blown head gasket and just went for it - getting the heads so hot that the oil crystalized. What oil didn't cake up sprayed completely all over the engine itself from worn out valve cover gaskets - making it for the worst clean job in history. I had to do a full rebuild on the entire upper half of the engine - including camshaft, tappets, pushrods, & rockers and arms. I've gone through your checklist and have replaced nearly the exact same things. It's complete - although I wonder on the fuel. But, that would be a serious long shot. You may want to consider the exact pressure of fuel - and maybe the fuel pressure valve in the back plenum right in front of the coil packs (driver's side). Also, check the vacuum hose - another really long shot. The other thing is the fuel really switch.

A dead crankshaft position sensor would mean you can't fire the vehicle. Hitting the starter would just turn the starter and roll the crank with no fuel or spark. So, you are correct on that. But, the camshaft position sensor may contribute to this as it is the one that roughly speaking tells the computer what to do and when. The camshaft position sensor is more brains than braun. It's located at the front of the engine right between the water pump pulley and main crank pulley. A bit of a pain to get to. It's all of about $20.00 to replace and that would be my only solid advice since you've taken care of every other single issue there is.

 

Wires are fine ohm wise
Plug gap is fine as plugs are sub 100miles old as of this posting, old plugs had fine gap as well and still had miss
Shuffling coil packs doesnt move the missifre
Checked the HV coil connections and they are clean as expected for new ones
PCV and oil separator were done
Throttle and passages are clean as well
Base idle is sitting at ~700rpm just below 750 mark which admittedly is a bit higher than 650-600 in rave but its not grossly low or at the 1k mark of failed sensor

Compression test needs to be done I agree.



Appreciate the solid feedback, my fuel rail pressure is ~35psi at idle and ~30psi at load. It doesnt feel fuel starved and the miss is mostly visible at idle so im presuming it is getting enough fuel.
Ive got a camshaft position sensor on the way and will update thread when I get that in. The wee little vacuum line on the back of the plenum is firmly seated on both ends and the car idles much worse when unplugging it which tells me its atleast blowing free.

 

Maybe check fuel pressure at idle when the (wee little) vacuum line is disconnected/capped (should increase to around 36 psi (2.5 Bar) if regulator, pump and filter are OK).

Not sure what you mean "at load". Is that when the transmission is engaged, but still idling? Higher vacuum at the regulator decreases fuel pressure to a certain minimum value but I think it only adjusts 0.5 Bar or 7 PSI (about 29 throttle closed to 36 psi throttle open).

There is a procedure for setting base idle that involves completely plugging the IACV pathway, (or getting the valve to close and unplugging the wiring). There is a path around the throttle with a needle screw hidden by a small aluminum cap, CW (less air) lowers base idle, CCW increases. Manual specifies 500 - 525 RPM or so (just barely keeps running). Count turns to remove it to see if it is clean. The higher RPMs you mentioned indicate the IACV is in control, but that is different than base idle, which is checked without the IACV being active. Getting base idle right ensures the IACV is operating in the best position.

Have you monitored the O2 sensors live data? Live data can show rich or lean conditions when voltage is pegged high or low, and helps know if the fueling is correct. O2 sensor problems can be a real bugger, it took me months to get mine straightened out, but now I know how.

 

Will check the wee little vacc line's relationship on fuel pressure and report back.

By at load I mean the car is in park and im revving it while monitoring the pressure on the schrader valve. Pressure drops as I rev it and quickly resumes as I let off. Based on your post it seems like I should be observing the opposite behavior? Could a clogged strainer or failing pump be causing a miss by starving 5? 5 is in the middle of the firing sequence so if it was fuel starve wouldnt I see it closer to the start or end of the sequence? Car doesnt feel like its bogging down at speed when hammering throttle, I can gas the heck out of it and get up to speed at about the pace id expect from a 97 v8 with brick aerodynamics.

Noted on idle air setting, ive seen the rave/threads about pulling that capped screw deal and moving it back and forth and assume thats what youre referring to in this process.

Ive done some live monitoring for the sensors and they are all individually reporting pass with readings being somewhere in the middle. What should nominal ranges be for these just so I can check?

 

Live O2 upstream sensors (B1S1 and B2S1) should show modulating between about 0.1 V and 0.9V crossing the mid point several times per minute. Low voltage is lean, high voltage is rich. The downstream sensors should follow the upstream, but less extreme if the cats are working.

On cold start, the engine runs rich. On my '96, after a minute or so (depending on temperature), the ECU will adjust the mixture and modulation begins.

Short term fuel trim and long term fuel trim for each bank can also be shown on live data and are important data points to show the engine is running well. My mechanic says long term fuel trim should be less than 5% for a sound engine. Max'd out at +/-25% shows a problem (+ is adding fuel, - is subtracting). Each bank (odd cylinders Bank 1, even cylinders Bank 2) is trimmed independently. Short term trims can be seen modulating along with the O2 sensors. O2s show the average value of the four cylinders on each bank. I don't think the firing sequence is a factor since trims are applied to all four cylinders equally.

I suppose if fuel pressure is not to spec and the #5 injector is "weak" that could cause a miss due to very short pulse time at idle. Maybe move the injector to troubleshoot.

So check O2 live data and long and short fuel trims. The Torque app can display all those simultaneously, along with RPMs and Engine Coolant Temperature.

 

regarding idle air control setting....DON'T mess with the screw. That is only for the 3.5 & 3.9's with a dizzy. I doubt air intake is your trouble.

JohnZo has done a good job reviewing what should appear. Additionally, base throttle on your truck is 11-14% at idle.

I'm not sure what live data you can see but a dongle and either the Torque app (android) or OBD Fusion (apple) will get you pretty much all you need in terms of monitoring, and reading/clearing trouble codes. Everything JohnZo mentioned is available for display.

Also agree on the fuel trim issue which I now suspect to be the culprit. You mentioned that you did head gaskets at 150k. What is the current mileage? You may simply need an engine ECU re-flash to clear all the old adaptive values the ECU has learned/stored over the years and start with a fresh fuel map.