Engine Shuddering

[SlowNsteady]

My engine seems to be shuddering way more than normal? Not sure if it’s just me but seems to be super rough. Also has a weak idle at times. It’s actually died on me on the freeway when I put it into neutral to slow down to go onto the offramp. When the engine is in neutral, sometimes I have to feather the gas to keep the engine on at a stop light. But when it does idle in neutral it almost always has this super rough idle and shudder. I couldn’t post the video here because it’s too long but here is the link https://imgur.com/gallery/vejNEJc

[NC85ST]

Have you tried adjusting the idle screw to make it idle faster. Forgot to ask, what are the rpm’s at idle now?

[SlowNsteady]

Just now, NC85ST said:

Have you tried adjusting the idle screw to make it idle faster. Forgot to ask, what are the rpm’s at idle now?

It looks like 500 rpm, from what I can see on the instrument cluster. I have not, I didn’t want to mess with the carb without a second opinion. Making sure im not making things worse 

[datzenmike]

500's too low. 650-750 is better.

 

Look for any hose disconnected or cracked that directly connects to the intake manifold. Don't forget the brake booster. When idling does it drop when you step on the brake???

 

Is this an automatic? There is a small vacuum line down to the transmission. Pinch the hose where it connects to the brake vacuum fitting. If idle improves it may have fallen off.

 

 

Check set the valve lash 0.012" hot.

Timing 3⁰

Is the choke flap fully off when warmed up?

Get a vacuum gauge and see what the idle reading is.

[SlowNsteady]

Ok I’ll take a look at all the hoses. This engine is all stock so there’s so many vacuum lines :l I haven’t noticed any drop when I step on the brake but I’ll Check that.

 

not An automatic. Manual. You can see the shifter shaking violently while I’m in neutral in the video I linked. 
 

I’ll set the valve lash, not sure how to do the timing. Would that be rotating the distributor? I’ll check the choke 

[datzenmike]

 

 

You'll need a timing light for setting the ignition timing.

 

Did it ever run properly and then just started doing this?

 

Is this a Z24i engine with two butterflies holding the air filter on?

[SlowNsteady]

ill get a timing light on payday

 

i just got this truck. It’s my second truck, but it was running fine when I bought it about a week ago. No idle issues, never died on me for the 4 days I was driving it. It just started doing this yesterday. I haven’t messed with the engine at all since I got it. 
 

Not fuel injected. You can see in the video on the link

[nicklp]

Have you checked the basic stuff? All electrical connections in the ignition system? Fuel pump/fuel filter? 

Edited August 12 by nicklp
Spaced

[datzenmike]

If it runs and drives but won't idle the filter and pump are ok.

 

If it was running ok before it won't be the timing or the valve lash so forget those. These don't go out of adjustment in a short time.

 

 

There will be a small sight glass on the front of the carburetor that shows the fuel level. Check if it's more or less in the middle. If float chamber is over filled it will flood and be over rich at idle. 

 

Pull all the plugs and keep in order, there are intake NGK BPR6ES and exhaust NGK BPR5ES. If you don't have NGK in these heat ranges time to change them. Do not buy the cheap ones from Amazon there are too many counterfeit one out there. Are any pair of them suspiciously cleaner than the others?? This would be an indication that coolant is leaking in from a bad head gasket.

 

Keep an eye on your radiator level. If it needs topping up weekly or sooner, it's a good indication that the head gasket has failed.

 

Again a borrowed vacuum gauge connected to the intake showing a low number say below 14 might be from a vacuum leak. Over 18 would be better.

 

 

 

 

 

[SlowNsteady]

Im assuming the ones at autozone won’t be counterfeit right? I’ll double the check the spark plugs but I was planning on replacing spark plugs, wires, and distributor / rotor min the next wave of improvements. I wasn’t sure. When the last time all of that stuff had been replaced so I just wanted to give them a little upgrade. 
 

I’ll keep an eye on the radiator, but it hasn’t overheated or gotten abnormally hot. I’ve driven it 100+ miles straight and no issue. 
 

yeah I’ll definitely just buy one. The vacuum lines on this truck are a little confusing. Should come in useful later too if I ever switch it over to a Weber. 

[SlowNsteady]

Random question: should I remove that asbestos like liner on the inside of the hood? My truck still has it. 

[datzenmike]

It will likely be fiberglass. Asbestos would never be used. It was used in the early '70s on Japanese heat shields on SU equipped coupes. If in reasonable shape just leave it. It's mostly a sound deadner.

[SlowNsteady]

Question: so I bought a second truck. 86 720 same as the first. However, this one has significantly more miles 340k approximately. I just replaced the spark plugs, the spark plug wires, distributor cap and rotor, retorqued the head bolts to 60ftlbs, and replaced the air filter in the stock carb. Before I took it, the gentleman I bought it from took it to get serviced, oil change, and all other fluid changes. He maintained it very well (has all the original paperwork and receipts for major maintenance) and he regularly has the oil changed. Is there anything I can do to prolong the life of the engine? I’m not sure if the bottom ends are safe for the most part, or if they’re prone to failure at 100k intervals like the head gasket. Would love to keep this truck going strong.  

[banzai510(hainz)]

a Napz motor?

340k miles?  I say its on borrowed time myself. pistons rings must be paper thin by now.  This is Toyota 22R territory for high miles or even Mercedes Diesel motors.

change the antifreeze every 3/4 years is the best as one can do to preserve the aluminum head./Dont over heat

 

Oilchanges I only do mine every 6months on a daily driver regardless of miles.

 

 

as for shuddering Im not a Newer Nissan guy as those motor have alot of emission hoses ect(vaccum leak)....... Carb could be clogged,Idle jet dirty. fuel filter needs repalcement.

Edited August 16 by banzai510(hainz)

[SlowNsteady]

Yeah I was surprised myself. The head was machined around 100k because of a bad valve Job and at 200k valve guides were replaced and cylinders were checked. They were within factory spec. Seems like the head is in good shape too. I drove it about 150 miles no issues. I guess my question is what should I do now as I prepare for its eventual failure? 
 

I don’t mind rebuilding a motor and doing a swap to prolong the life of the truck. Would it be worth the trouble to rebuild it myself or should I just wait and order a rebuilt engine or should I have the current one rebuilt? 

[datzenmike]

If it was maintained (tuned, regular oil changes, fix things that go wrong/wear out) there is no real upper end resulting in failure. It will inevitably slow down. There is nothing wrong with L and Z NAPS engine bottom ends to be worried about. Next oil change make sure to specify WIX filter or NAPA Gold just about anything but Fram. As for oil, starting around '92 oil makers started dropping the ZDDP content so that today it is about half what it was when your engine was designed. About 600-700 PPM today.  ZDDP is an anti scuff additive that protects cam and rocker contact areas. Newer cars don't need it and it buggers up the catalytic converters. I use 10w30 Shell Rotella T4 which is a diesel oil that is exempt from this and maintains a 1,200 ppm ZDDP.

 

Other than that, keep it maintained and fix/replace things as they wear out normally and happy motoring.

[SlowNsteady]

Thank you for the advice, I’ll make sure that the right oil is used. Would that have any impact on crank bearing life? 
 

On the subject of replacing things.  My fuel pump is knocking really loud. Is this normal? Is it time to replace? Here is a video of the fuel pump I took 30 minutes ago after I replaced the spark plug wires, spark plugs, distributor cap and the rotor. https://imgur.com/gallery/S81WoSi

[datzenmike]

I doubt it, all newer cars have crankshafts, rods and bearings. So no.

 

That is not the stock 720 pump so I have no idea how loud it can be.

[Sephakrid]

On 8/11/2024 at 11:20 AM, SlowNsteady said:

My engine seems to be shuddering way more than normal? Not sure if it’s just me but seems to be super rough. Also has a weak idle at times. It’s actually died on me on the freeway when I put it into neutral to slow down to go onto the offramp. When the engine is in neutral, sometimes I have to feather the gas to keep the engine on at a stop light. But when it does idle in neutral it almost always has this super rough idle and shudder. I couldn’t post the video here because it’s too long but here is the link https://imgur.com/gallery/vejNEJc

 

My truck will sometimes idle like that (maybe not quite as bad) during warm-up. Once the coolant temperature stabilizes, idle RPM increases to about 700-800 (measured with timing light) and the engine smooths out significantly.

[SlowNsteady]

Yeah after this weekend riding around I noticed the same thing happening to mine. It didn’t die on idle after being warm but definitely once or twice on a cold start 

[datzenmike]

Try turning the idle speed up. Idle 650-750.

 

During warm up the engine is not operating at it's best efficiency so the warm idle and mixture setting don't help. The carburetor mixes gasoline spray (not a vapor yet) with air. On the way to the combustion chamber the warm intake runners, the warm head ports, the hot intake valve the hot combustion chamber and the piston as well as the compression all contribute to vaporize the fuel. On a cold engine a choke is used to make the mixture richer which makes it easier for the oxygen to find enough fuel vapor to burn more efficiently. A fast idle cam is also employed to rev the engine and make it warm faster.

 

If the choke is not set properly or stuck or the fast idle cam stuck it will run rougher than it needs to.

[SlowNsteady]

Random question, is there a Nissan 200sx category on the website? I found a 1987 one and I saw it doesn’t have a very strong community behind it. I figured maybe there was one here? If not do y’all know anything about them would it be wise to buy one? 

[Logical1]

10 minutes ago, SlowNsteady said:

Random question, is there a Nissan 200sx category on the website? I found a 1987 one and I saw it doesn’t have a very strong community behind it. I figured maybe there was one here? If not do y’all know anything about them would it be wise to buy one? 

 

https://ratsun.net/forum/22-other-datsuns-and-nissans/

 

It is a mix of the many models that are not as prolific as the others but you can find some good info in there!

[datzenmike]

53 minutes ago, SlowNsteady said:

Random question, is there a Nissan 200sx category on the website? I found a 1987 one and I saw it doesn’t have a very strong community behind it. I figured maybe there was one here? If not do y’all know anything about them would it be wise to buy one? 

 

The S12 from '84-'88. The '87 model introduced the VG30E engine replacing the CA18ET and continued through '88. This was the same engine used in the earlier 300zx non turbo through '87. The '87 and '88 also had the CA20E NAPS engine. What'd you get???

[SlowNsteady]

2 hours ago, Logical1 said:

 

https://ratsun.net/forum/22-other-datsuns-and-nissans/

 

It is a mix of the many models that are not as prolific as the others but you can find some good info in there!

Thank you so much! 🙏