[TWX]

Neighbor sold me his 86,000 mile '95 Nissan Hardbody 4x2 2.4L 5 speed, he'd fairly harshly overheated it when the upper radiator hose broke the nipple off of the radiator.

I've since fixed the cooling system (basically flushed the water jacket on the block, replaced all rubber, replaced the radiator, the thermostat, the thermostat housing), changed the oil, checked the compression both cold and hot (avg 150psi cold, avg 160psi hot, high-low range across four cylinders less than 10psi under each condition), changed the plugs and wires, changed air filter, replaced the blow-by hose between the valve cover and the air cleaner.

It ran really rough at first but seems to be getting better, but the idle is still rough. The tachometer also doesn't read-out correctly, tending to hover just off-zero at idle, and to reach maybe 1500 while driving. Occasionally it wants to show the right readout, it'll jump up, but then come back down.

I'm not sure if the two symptoms are related. I've already checked the throttle pressure sending unit, got about 0.57V at idle, about 4.09V at wide-open, with hot-to-ground of 5.13V. Haven't checked anything else under the hood yet. I do need to replace some of the plastic between the air cleaner and the fresh-air intake, but that stuff shouldn't be causing any particular problems.

When I first got it running I got a small smattering of codes, a Code 43 (TPS), a Code 41 (something about an air temperature sending unit), and there *might* have been a Code 32 (EGR sensor). I tested TPS before I thought to reset in case any/all of these codes were from error conditions caused by the overheat. After resetting and driving probably 30 miles I haven't gotten a CEL, but the rough idle seems to persist, along with the tach problem.

Any suggestions would be appreciated.

 

[Bob Lincoln]

Bet the overheating cooked the head gasket. I'd check for all signs of imminent gasket failure: compression, oil-in-coolant, coolant-in-oil, exhaust gas in radiator, overflow jug filling up, etc. The last head gasket failure I had, showed up as rough idle and loss of power, rapidly getting worse over a drive of about 15 miles. The metal rings between cyls 2 and 3 burned away, so that the cylinders were pumping into each other.

 

[TWX]

Good compression so far, ~150PSI cold, ~160PSI warm. Will check again, was planning on changing the oil a couple of times and possibly flushing coolant a couple of times, what was left in the cooling system was rusty enough that it might have been just water.

 

[ImperialCrown]

A compression test probably won't tell you what you need to know here. The compression stroke pumping of the piston is much too fast to catch a slower leak, like valves, rings or h/gskt.
A cylinder leak-down test applies air pressure to the individual cylinders (with the valves closed) and you listen for air escaping (hiss) from an adjoining spark plug hole (h/gskt), throttle body (intake valve), tailpipe (exhaust valve) or oil filler cap (piston/rings).
Spark plug tip color for each individual cylinder can also tell a story.

 

[TWX]

Okay. I think I have the tools to do a leak-down test, but I'll have to fix the portable air tank where it's leaking at the fitting. Figure start with the portable tank at 125psi, pressurize the cylinder, take a reading, come back some time later and take another reading?

Plug tips were pretty nasty when I pulled them, but I don't know how much maintenance this thing got either. Clutch is very awkward, it grabs suddenly pretty close to the floor when letting-off, so at a minimum I need to bleed the clutch and see if that helps. It doesn't slip at all so I don't think that it's actually bad inside of the bellhousing, but it's a pain to drive.

A CEL came on as I headed to work, turn around and parked it and took another vehicle. Will pull the seat and check codes when I get home. Wish that the computer was in a better spot...

 

[ImperialCrown]

If you apply air pressure to the spark plug hole and the cylinder exits are sealed, you should be able to determine if there is a leak right away. Just listen for the hiss and locate where the air is escaping from.

 

[TWX]

So I need to be at TDC between compression and ignition strokes then...

 

[Bob Lincoln]

Yup. So turn the engine by hand until you are at TDC by the timing mark, and if you hear a massive leak, that means you need to rotate the crank another 180 until you are at the top of compression stroke and both valves are closed.

 

[TWX]

Update, haven't done a leak-down test yet, but did pull the seat and checked codes.

Got 32, EGR FUNCTION, no other codes, and I had cleared the codes over the weekend and hadn't thrown another CEL until this morning.

My question, is this a pretty realistic indicator that the EGR valve is actually bad, or are there other things that can cause this DTC? It's been a long time since I had to replace a bad EGR valve and it was on the 360 in the Cordoba, I think these symptoms are similar but again, been a long time. Also, since the EGR valve probably isn't something that's easy to swap between the two trucks I'm disinclined to swap to test, but would rather avoid throwing parts at it willy-nilly.

 

[ImperialCrown]

An EGR that was flowing too much exhaust into the intake mixture at idle would cause a rough idle and rough lower speed operation.
Pulling the EGR vacuum supply hose at idle, it should have very little or no vacuum at idle. The EGR vacuum modulator is before the EGR valve and may be supplying vacuum all the time if it is defective/leaky?
Or the valve itself may be defective (open all the time)?
Chrysler services both its EGR transducer and EGR valve together. Nissan may or may not do the same?

 

[TWX]

Alright, I'm going through the diagnostic procedure for EGR, "Procedure 29".

One of the steps is to check for voltage between the ECM on the pin for the wire from the EGR system, to ground. At 2000RPM this voltage should be battery voltage, and at idle this voltage should be 0V.

I'm getting battery voltage at idle. Unfortunately the rest of the diagnostic procedures seem geared toward getting 0V at 2000RPM, as opposed to getting battery at idle.

Suggestions are appreciated.

We did warm up the vehicle enough that the coolant was circulating and the valve cover was hot to the touch.

 

[TWX]

Did some further disassembling and found the little 1/4" ID hose between the EGR valve and the component right above it was very, VERY bad. Like that gooey, barely not a liquid kind of bad. Replaced that, replaced several other 3/16" hoses that were also showing signs of being worn.

Cleared codes and road-tested. no new codes this time. Idle still isn't perfect but it is better. Tach still doesn't work properly, and the idle speed screw on the computer doesn't seem to be doing anything either.

 

[Bob Lincoln]

"idle speed screw on the computer" ???????????????

 

[TWX]

Trust me, that was my reaction originally too.

Computer has only one control. There's a screw that acts as a knob. The position of that knob is supposed to tell the computer the technician's preference for idle speed. When that screw is turned all of the way clockwise it then starts the computer cycling through various diagnostic modes, of which one is to display stored codes, which blink on a pair of LEDs next to the screw, red for tens-digit, green for ones-digit. Red also happens to be tied to the output for the CEL on the dash cluster.

To get to the computer the seat has to be removed as it's under the passenger's seat on the floor, and the computer has to be unbolted from the floor to easily reach the screw and LEDs. four bolts with 12mm heads for the bucket seat, three screws with 10mm heads or #3 Phillips for the computer.

 

[TWX]

Wife helped me bleed the clutch. It's still grabby, but the pedal range is a little better and more predictable. Still might need a clutch replacement, we'll see.

Since replacing that 1/4" ID hose haven't gotten a CEL. Did probably 20 miles of mixed city and freeway mileage, so far so good. Stumbled across my old tach/dwell meter, checked RPM on the engine, it's actually idling around 850RPM. Doesn't sound like that to me, but I think I'm hearing various rattles that I'm not used to so I was thinking it was worse than it is.

Did some poor-man's body work, Pushed the core support back out through the wheel-well, which pulled the fender back in, fixed what needed it (didn't damage paint enough to bother needing to touch-up) and swapped bumpers and some other parts between the two trucks.

Started trying to straighten the bent bumper enough to put it on the other truck, didn't get very far on that. It'd a bit difficult to position it on the 20 ton press, may have to rethink how I go about straightening it, or see if I can find a cheapo bumper that's in better shape than this one to put on the other truck.

Tach in the truck still doesn't work, tonight's roadtrip showed me that much, but otherwise it's feeling very good. Will probably drive it to work over these next few days to see how it does, and possibly stop by a couple of wrecking yards to see if I can find a dashmat and a couple of good sun visors, and maybe a center console out of a '98+ Frontier to swap in to get some half-decent cupholders.

 

[ImperialCrown]

The clutch itself may be OK if it is an early engagement issue. The clutch actuator hydraulics could still be worn/leaky and need replacement.
Bleeding may help in certain cases, but ask yourself how air got in there in the first place?

 

[Bob Lincoln]

If you are used to a cable-actuated clutch, all hydraulic clutches feel grabby and especially just as you lift the pedal off the floor. I get far better modulation with a cable-controlled clutch.

 

[TWX]

Well, it's very, VERY different feeling than the clutch on the existing truck. Both are hydraulic. The existing truck is almost too soft though.

I couldn't find any sign of leakage underneath. The more I drive it the better it feels, we'll see if it gets any better. Old fluid was brownish-orange, we pumped fluid through until it ran pretty much clear.