# D21 Runs Rough



## spikesc (Mar 3, 2008)

Hello Everyone,

I know things like this are so difficult to help diagnose over the internet, but I thought I'd share whats going on this my truck with everyone in hopes that I might get some ideas about what it going on.

I have a 1991 2wd 4 cylinder D21 automatic with 104K on it. I've owned it for the last 4 years and 55k miles. I change the oil every 3-4k, use filters with anti-drain back valves, good oil, changed the timing chain at 85k, change the fuel filter every year, flush the tranny every 30k, tune ups every 20k, ect. I take good care of it. My truck doesn't burn any oil, typically runs great, and gets 25mpg.

On Friday the truck was running good. I parked it at home and left town for the weekend. On Monday morning after it sat all weekend, I jumped in my truck and started it up. Now, it's running very rough, like it isn't firing on a cylinder or something. I tried to drive it down the road, but is has very little power and runs very rough. 

After work today, I pulled the passenger out seat out and checked to ECU codes. In mode 3 (indicated by 3 simultaneous red/green flashes and selected by rotating the selector counter-clockwise following the 3 flashes) I'm getting 5 red flashes and 5 green flashes, so no ECU error (right?). I pulled the plugs and they all look the same and quite good. The cap and rotor have about 15k on them, I inspected both and they look good. Since the ECU isn't showing any codes, I'm thinking that the problem must be something that it doesn't monitor.

Next, I'm thinking that I'm going to try replacing the fuel filter (it's been a year) and ignition coil (it's the original). If that doesn't resolve things I may go with a new fuel pump next if the fuel pressure registers low. Could it be a stuck valve?

I'm not sure what is going on here. Any ideas or tips for trouble shooting this would be greatly appreciated. I'll keep you all posted on my progress.

Thank you,
Colin


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## zanegrey (Dec 5, 2005)

no matter that the truck has low miles no matter your mantinance ..with a truck that old you must consider the timing chain..does it rattle ?


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## smj999smj (Jan 1, 2006)

First of all, I wouldn't recommend replacing parts that aren't diagnosed as being bad. If this happened after a bad rainfall, inspect your ignition wires and distributor cap and rotor. If you find moisture in the distributor or signs of corrosion, Nissan developed a new distributor, cap & rotor with better venting to correct this problem. Distributor assy. is P/N: 22100-1S704RE, distributor cap is P/N: 22162-3S505. Check for vacuum leaks at rubber hoses, intake gasket (spray carb cleaner around intake gasket with engine running, listening for a sudden change in RPM), or stuck upon EGR valve. If you suspect low fuel pressure and new filter doesn't change anything, get a fuel pressure gauge and check the fuel pressure...especially before going through all the expense and time of replacing the fuel pump! Check your ignition timing with a timing light; if the chain did jump a tooth, it will also throw off the ignition timing a few degrees (usually about 8 degrees, retard) as the distributor is driven off the camshaft. If it's a dead miss on one cylinder, remove one plug wire at a time (with insulated spark plug wire pliers) to locate the dead cylinder. The RPM will not change when you remove the spark from the weak or dead cylinder. You could also do this by disconnecting the fuel injector harnesses one at a time, but this can be tricky and the plastic connectors get brittle with age and the heat of the engine. Idenify the dead cylinder, and check the plug, fuel injector and do a compression test (remove all plugs before the compression test.


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## spikesc (Mar 3, 2008)

*Update*

Today's Tests Observations
1. I tested the compression, it's even and 125psi on all 4 cylinders (it's 50 degrees outside and the engine was completely cold).

2. I noticed that #2 spark plug was slightly darker then rest and a little wet. The moisture looked like a light cover of oil or unburnt gas, hard to tell. Any tips for tests to ID the liquid?

3. When I remove the #2 spark plug wire, the running condition (looping, rough) barely changes. When all other spark plug wires are removed, the engine runs much worse.

4. I swapped around spark plugs and wires to rule out a faulty plug or wire, no change when I did this.

5. I tested the spark to #2 with a ground, it seems to have a strong spark

6. I changed the fuel filter and ignition coil to rule them out, no change.

Next Steps
1. Get timing light from storage and see if the timing jumped a tooth

2. Test fuel pressure

3. Check Injectors as smj recommended by carefully unplugging one at a time

4. Continue to inspect wires and vacuum lines. I live in an area with a lot of little creatures (squirrels, mice, rabbits, coyotes, deer, ect.) I noticed some signs of squirrels or mice. But I had some in the engine bay 3 years ago and these signs I'm seeing could be that old, hard to tell.

5. Check for vacuum leaks

6. Remove valve cover and inspect timing chain condition

Questions
Could a faulty valve that is not opening be causing this problem? How can I test for a bad valve? Can I remove the valve cover and spark plugs and manually turn the engine over to observe/measure valve clearance? I've adjust valve clearance on pushrod inline-4's (B18 & B20 Volvos).

Is it reasonable to suspect a bad valve because the spark seems strong, compression is even and #2 cylinder observations mentioned above?

I plan on removing the valve cover for inspection, any tips on what to be looking for in the context of the issue described?

Responses
Zane: Since replacing the timing chain 15-20k ago I haven't heard the characteristic rattle of a bad timing chain. I will test my timing to see if it jumped a gear. I also plan on removing the valve cover and inspecting the chain, cogs, guides, and valve timing (if possible without removing the chain cover).

smj: Thanks for you response. I live in rainy Washington State, the truck is often driven in heavy storms. The weekend that this problem suddenly occurred it did not rain.

Thanks for your help everyone! I know this is a long thread, but there is a lot of info here and I tried to break things up for readability.

Colin


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## smj999smj (Jan 1, 2006)

If the chain jumped, it would have showed up in the compression test, which should have been done with the engine warmed up, but that's okay. You've already isolated it, it sounds, to #2 cylinder, so why you wasted money on a coil, I don't understand as a bad coil would affect all cylinders. Concentrate on #2 cylinder. I would make sure there is no intake gasket leak, esp. at intake runner #2. You could also have a leaking fuel injector at #2. A fuel pressure leakdown test would help confirm. During a cold sit, a leaking injector will drip gas onto the top of the piston, usually resuting in a gas fouled spark plug when starting. I seriously doubt that the valve clearance is an issue unless something broke. No use in unplugging injectors one at a time as you already isolated the misfire to a cylinder.


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## glider429 (Nov 18, 2010)

Hey Spike I have a 91 Hard body 2wd 2400 doing the exact same thing as yours did. It started just a couple of days ago. It was running fine then I parked it and went out the next day and it was running like crap. It sounds like it is missing or starving for fuel and cuts out all the way to the top then smooths out a little on the top. No codes other than the 55 which bites cuz that means it's all good.

I checked the rotor and cap I cleaned them up plus they were just changed not long ago.

Then I replaced the plugs and wires, I did not change the coil because I know those tend to go all at once. The #1 plug looked a little wet but not bad. I did pull the #1 plug wire off while it was running not much difference.

The timing chain was done about 15k ago I know that's not it.
Don't think the timing is off.

It doesn't sound like the valves are an issue but I'm not ruling it out. It does have a little miss sound coming out of the exhaust. 

Next I'm gonna check the injectors.

Any other suggestions or did you ever resolve the problem?


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## martin.maurice (Nov 14, 2010)

take precautions and spray flamable car cleaner around the intake manifold where it bolts to the Cyl head. You'll find #3 or #4 intake manifold gasket has cracked sucked in now the engine idles roughly some times it even sets a p0300 code. Not easy to get to the bottom manifold bolts and nuts. Plan a whole day of drive way cursing and cussing. Be sure extra sure you have all the gasket cleaned off before placing on a new gasket. Water passageways under manifold. while your in there now you can see the PCV and several radatior hoses that have been seeping.


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## Gdell (May 30, 2020)

spikesc said:


> Hello Everyone,
> 
> I know things like this are so difficult to help diagnose over the internet, but I thought I'd share whats going on this my truck with everyone in hopes that I might get some ideas about what it going on.
> 
> ...


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## Gdell (May 30, 2020)

I would definitely be suspecting vacuum leak...just found a strange one on my 94 nissan hardbody...even check the pcv hose...tighten the intake manifold if bolts are a bit loose as they do loosen up over time...also the wires going to the distributor...wiggle wires around the throttle to check for bad connection and see what happens


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## rogoman (Dec 16, 2004)

spikesc said:


> Questions
> Could a faulty valve that is not opening be causing this problem? How can I test for a bad valve? Can I remove the valve cover and spark plugs and manually turn the engine over to observe/measure valve clearance? I've adjust valve clearance on pushrod inline-4's (B18 & B20 Volvos). Is it reasonable to suspect a bad valve because the spark seems strong, compression is even.


It looks like you've determined the #2 cylinder not working correctly. Since the ignition to the cylinder tested OK and the compression tested OK, then it could be due to a dead or leaking fuel injector.

The fuel injector may not be firing. This can be tested with a "noid" light probe kit that gets connected on the injector harness connector; the probe kit can be puchased at most auto parts stores or online at Amazon.com.

A good way to test for a leaking fuel injector is to Tee-in a temporary fuel pressure gauge between the fuel feed hose and the fuel rail. Turn the ignition key to the run position but *DO NOT TRY TO START THE ENGINE*; then turn the ignition switch off. The fuel pressure reading should be around 43 psi which would be a static reading. Now watch the gauge; if it starts dropping down fast, that's an indication of a fuel injector(s) leak.

To fix leaking injectors, you can try to run a good injection cleaner, like BG products 44K, through the system; it's one of the best cleaners on the market; many of the cheap cleaners simply will not do the job. Give the cleaner about a week or two to do it's job. After the treatment, recheck again with the gauge. If it's still leaking, the best thing you can do is replace all the injectors rather then trying to figure out which is the bad one.

To test for bad valves, you would use a cylinder "leak down" test kit. A leak down or "cylinder leakage" test is similar to a compression test in that it tells you how well your engine's cylinders are sealing. But instead of measuring pressure, it measures pressure loss. The neat thing about a leakage test (as opposed to a compression test) is that it's faster and easier to figure out where the pressure is going. If you hear air coming out of the tailpipe, it indicates a leaky exhaust valve. Air coming out of the throttle body or carburetor would point to a leaky intake valve. Air coming out of the breather vent or PCV valve fitting would tell you the rings and/or cylinders are worn.


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## Ser spec-d21 (Apr 20, 2021)

I too have this problem and I bought/swapped everything out. transformed it into a 240sx motor. only to find out the filter fell off and a tiny piece of rubber was wedged in my new fuel pump. cleaned it out dropped it back in and wow man rocket ship kind of blast off. msd 6al didn’t help aem wideband hardly showed hints of it go figure new 240 injectors fixed nothing and still it was number 2 looking fouled all to heck.thought valve or dead cylinder from low compression always number 2 in my case. don’t understand it figured my junkie maf set up was to blame but no it was fuel pump.blew my mind just thought I’d put that out there sorry. I’m new to this posting thing but I had to let it be known. Hope it helps might try pinching off the return line with vice grips and see if anything changes a bit. That’s a hind sight is 20/20 suggestion won’t be a big change because volume wouldn’t be as great even though the pressure is increased if you have blockage I think idk... hard bodies are pretty cool?


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