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LugNut1990 06-23-2018 07:21 PM

Misfire / engine shake at idle: KA24E
FYI -- I'm the original owner of this 1990 4x4 with the KA24E, with around 110K miles on it. I don't drive it that often, but have daily for the last few weeks while hauling light loads on a ~15 mile round-trip each day.

It's developed a bad idle (got worse slowly over the weeks) / consistent engine shake (at low-idle speed), but runs like a champ above idle. I can't be sure if all four cylinders are firing above idle, but I suspect so.

Diagnoses/observations so far:

Definite, consistent putt-putt out the tailpipe, with lots of condensed water coming out. Exhaust smells like the cat is working hard, with no raw fuel odor coming out.

Idle's timing is fine at 10 degrees BTDC. Via the timing light's pickup on each spark plug wire, there's consistent spark to each cylinder.

Taking the air cleaner off, all hoses appear attached and in good condition all around the engine and brake booster.

The engine oil looks and smells fine -- no gas odor, for example, and no oil use.

With the engine idling (badly), pulling the dipstick doesn't affect the idle. Opening the oil fil cap does only very slightly, but I'm getting strong, consistent air pulses coming _out_ (where I was expecting airflow in, and poorer idle).

Wiggling/pushing down the injectors' connectors made no difference.

Air intake temperature sensor looks clean, but cleaned it anyway with MAF spray. Haven't check the MAF in the TB, but the throat of the TB looks very clean.

No CEL, if this non-California truck even had one. The OBD1's mode III gave a code 55, meaning no bad sensors detected (I do have the 1990 FSM). Couldn't quickly figure out the mode I and II readings ... what a PITA this OBD1 is compared to OBD2!)


Engine is cooling-off now, and will pull the spark plugs this evening, hopefully.

I just bought a paint-can smoke tester, so can use it if needed.

All replaced, in less than 10,000 miles (but may have been years ago):

EGR and PCV valves
Plugs, wires, and distributor (and its cap)
Oxygen sensor
Cat converter; EGR crossover pipe as well as the header pipe (OEM)

Coolant temperature sender (I think)
Fuel injectors
Air and fuel filters
Valve cover gasket

I do have a slow oil leak from the timing cover -- I need to replace the head gasket to fix it (have parts in hand, but not planning to get to it soon).

I have suspicions to the cause, but no definites. What say you?

If you have a KA24E, I'd appreciate you trying: at idle/parked open the oil fill cap -- what airflow do you observe through the fill port in the valve cover? In/out? Pulsing/smooth? Idle gets worse/no big change? :confused:

johnber 06-23-2018 08:32 PM

take a compression test and if it comes out ok tune it up. sounds classic bad valve to me.....but ignition can cause it too. As far as the puffin out the v/c.....they ALL do that.

LugNut1990 06-24-2018 12:34 AM

All four plugs (NGK ZFR5E) evenly "worn" and not oil or gas soaked. All gapped at 0.040.

Compression test: 149-150-150-151

So ... with your "all do that" (oil fill cap pulsing/flow out) and the above compression numbers, I can thankfully rule out a hole in a piston. No valve tapping, so I think I can rule out a stuck intake valve/collapsed spring.

When I have a chance I'll check/clean the MAF sensor and check its resistance. Other ideas? Or will figuring out the OBD Mode I and II diagnostic possibly give a clue?

LugNut1990 06-24-2018 02:21 PM

Bought this early a.m. and installed new plugs of the same type (I don't like to reinstall a full set of used plugs, unless near-perfect/clean). 0.044 gap. Moved the newish wires to make sure no two were touching.

Started fine, and no evident misfire at high-idle. But about a minute later, when low-idle kicked-in, misfire/shake returned.

Interestingly ... a slight valve tap did happen at this start-up. Engine/truck had been sitting all night, inside the garage, with no plugs installed, and had been cranked but not started maybe a total of 30 seconds for the compression test.

New, high volume oil pump, as well as new OEM rocker arms/lifters, were installed in the not-too-distant (by miles) past. OEM oil filters being used "lately" because I hear they have anti-drainback valves that work.

No more time this a.m. (or possibly today). I think I'll do the MAF cleaning, smoke test, then check for a bad injector unless y'all have better ideas. The new injectors-set had only a one year warranty, so maybe they are :censor:.

LugNut1990 06-24-2018 11:37 PM

Problem found?
A productive couple of hours found today!

Pulled out and cleaned the MAF, despite it looking very clean already. Once every 28 years is this service interval? :dathumb:

Then used the new paint-can smoke tester. Here it is as installed for operation:

And a closer-up pic showing, for example, the latex glove on the valve cover (to air cleaner) hose -- a standard trick for limiting the pressure during the test), and the metal-backed HVAC tape used to seal-off the throttle body's openings:

And ... three leaks found! 1) Very small, at the head gasket to timing cover, where the slow oil leak is. 2) Moderate, from the "B.P.T. Valve" (diaphragm valve that decides if the EGR valve should open or not) -- the FSM shows, in a cut-away drawing, that the B.P.T. intentionally vents to the atmosphere so I think it is OK. 3) Fairly big leaks at the fuel injectors-to-intake manifold grommets, especially at #1 and #2. #1's grommet is so bad that the injector is slightly cocked to the side and thus may be the cause of the misfire. I don't remember if I replaced these grommets with the injectors a couple of years ago, but I would guess not.

Anyone bought/replaced these injector to manifold grommets? If so, where did you get them? If OEM, have the part number(s)? I do see aftermarket "o-rings" on Rockauto for this D21, but also warnings on other webpages about many not fitting correctly.

SBJ 06-24-2018 11:59 PM

I did mine a couple years ago. They were part of a cylinder head gasket set I bought on rockauto and have been working just fine for the past two years. The hardest part is making sure they seat all the way down. The ones that go into the manifold are usually fine but the ones where the injector goes into the rail can be a bit tricky. It helps to lube them with a little bit of gas first. Also turn the key on and prime the fuel pump when you're done. You'll know pretty quickly whether or not they're seated.

LugNut1990 06-25-2018 10:52 AM


Originally Posted by SBJ (Post 505832)
I did mine a couple years ago. They were part of a cylinder head gasket set I bought on rockauto ...

Thanks, and so close! (A fast solution for me) I have the FEL-PRO HS9646PT "head set" on the shelf, from RA too, for replacing the head gasket. Just opened it this morning, and no injector seals. Their website shows that they are not supplied in this kit. :(

So ... will pull the rail this a.m. and go hunting locally for the seals (with used one in hand for comparison). If not found, will have to mail-order. I did find the OEM part number.

LugNut1990 06-25-2018 03:40 PM

Pulled off the rail and removed the lower seals to take with me (glad I did). Local Nissan dealership didn't have the seals and would have to order them.

Advance Auto's aftermarket seal looked shorter and less beefy.

So I just mailordered the STANDARD MOTOR PRODUCTS SK40 seal kits (x4) -- hopefully to be delivered by the end of the week.

Side note: The truck wouldn't start this a.m. at all with the fuel pump's fuse pulled first. I was expecting residual fuel pressure from yesterday. Put the fuse in, and after a couple of seconds it did fire. Then pulled the fuse again and it died, as expected, after a couple of seconds. Is there a check valve in the fuel line after the pump? If so, I'd guess that mine is bad.

jp2code 06-25-2018 04:14 PM

Catching up on this.

I don't think there is a check valve in the line.

The fuel filter is 1-way, so that's probably all you've got. I hooked my fuel lines up backwards when I did my injectors about 5 years ago. The engine just doesn't fire at all like that! lol

LugNut1990 06-27-2018 10:26 PM


Originally Posted by LugNut1990 (Post 505876)
So I just mailordered the STANDARD MOTOR PRODUCTS SK40 seal kits (x4) -- hopefully to be delivered by the end of the week.

Just got 'em -- that was fast. Too fast! No time to install them today.

The seals that go in the manifold look much better than the BVP (?) ones that were available locally. Much taller.

Looking on-line, I'm seeing that the KA24E had different fuel rails. Mine's the one where the injectors stick out of a square bar. The other (newer? Hitachi?) one I'm seeing on Youtube, etc. has round holes that the injectors sit in, and apparently are hard to remove. Anyone know who made the square-bar ones, and what years HBs they were on?

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