Quiche2192

Relatively recently bought an S14 with this engine and have been having this issue from the start:

After just starting and then driving the car (so under load), it revs up ok, but only up to a point. I have to baby the throttle though. If I plank it, the engine doesn't pick up and ends up sounding rich. If I'm smooth on the throttle, it revs up nicely.
In the lower gears, it'll rev up higher, but in 4th gear for example, it'll rev up to around 5k and hard cut and stay there. So I could be at full throttle, but the engine will not pick up and sound kinda rich (breaking up), staying at 5k rpms. It'll do this consistently, hard cutting at around the same rpms.

Then, after running for a while, it gets worse, with the car not even being able to rev up from idle without sounding like it's being flooded by gas.

Another thing:
Mechanical timing looks fine, but when using a timing gun, I see around 22 degrees, instead of the recmmended 15. If I put it at 15, the engine runs like crap. Put it back at 22, engine runs fine.

I've checked and changed the following after reading up on older posts, so I did search around
- Mechanical timing looks good, as does CAS (I carefully checked this after making sure how to do it, so I'm pretty sure it's good)
- No boost leaks
- TPS is operating in the correct voltage range
- Replaced knock sensor (was getting code 34, not getting it anymore)
- Replaced and gapped spark plugs to .025 inches
- Replaced coil packs

Things I suspect but haven't checked carefully:
- O2 sensor
- Fuel injectors
- MAF sensor
- Ignition amplifier

Thanks for any input!

Kingtal0n

1. pressure test to 15-20psi of 'boost'. DO this in a quiet place so you can hear ALL leaks. Don't rely on smoke tests or carb cleaner based tests. Many leaks will not appear until pressure is applied. make sure you do not pressurize the crankcase in the process. Disconnect fresh air vent tube and pull out the dipstick to be sure. Listen in the dipstick for air flowing. It shouldn't pass much if any air in to the dipstick/crankcase region if the motor is healthy.

2. COmpression test and write the numbers dowm. Use a decimal place.
WRITE IT DOWN!

3. Do another compression test with a different tester, you may be surprised at the varied results. Never rent a compression tester either unless emergency.

4. leakdown isnt necessary but its good to know

5. make sure all the oem plumbing is in place for the maf sensor (inlet maf tube) the recirculated bypass valve (some kind of recirculating unit like greddy type-S)

You really need a bypass valve recirculated for the maf to be happy, and a nice long inlet maf tube pre-turbo to keep the maf from being buffeted by the turbo.

6. Timing test. Check the timing. Disconnect tps sensor and move idle speed to the factory range for timing to be 15*~
Double triple check you are using the right clamp direction (FLIP THE TIMING CLAMP AROUND) The CAS should be ALMOST centered in the head (center of the bolt holes more or less)

7. Physical timing (mechanical) 10 and 12, lobes outward, etc...

8. make sure the ECU matches the maf sensor (#62 redtop ecu goes with I think a 00F or something sensor I forget) but they need to match

9. For diagnostics from this point you will be disconnecting the O2 sensor to prevent closed loop.

10. New plugs, BKR7ES iirc, cheap coppers for now, gap to .035 or 0.032", never go below 0.030 unless you are making the serious boost 19+psi

11. Wash everything with soap and water except the maf and cas. clean the engine bay up completely to look new so you can spot leaks.

12. post pictures so we can see and help with whatever is going on in there

13. inspect turbo wheel /take a picture of the wheel / check for end play (front to back movement is BAD) side to side should have a little but not excessive.

14. get a AEM gauge wideband and use the wideband to further diagnose running conditions. widebands are installed at least 4 feet from the turbo. do NOT put it right where the narrowband goes. It will work fine there most of the time but if it gets hot enough it will report the WRONG a/f values.


15.don't mess with the tps, it isnt a problem 98% of the time unless somebody moved it significantly or cut the wires etc... the motor will still run fine without it (try it)

16. Ignition 'amplifier' is just a transistor (driver) it either works or doesnt work. If the motor fires all 4 then its fine.

17. Fuel system check. maybe this is like #2 on the list (not ordered I guess). Make sure fuel pressure is 'normal' (I run 38psi of base pressure but the factory regulator isn't adjustable so whatever you have make sure it matches). factory is 44psi baseline usually. The vacuum signal drops the pressure while engine is at idle/running etc... I am sure you know how that works right...
use a new fuel filter, Z32
Inspect the lines and make sure the pump is high quality enough to support your power range (stock is not good). 255 style pump is fine but I recommend a 'stealth' intank pump or similar (AEM makes one also)
for each 1psi of boost the fuel pressure goes up 1psi also. If you can verify this is happening from the driver seat with a gauge or some monitoring logging equipment all the better. Otherwise you will only have wideband data and that doesn't tell the full story. For a stock engine it should suffice though.

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EFITTZY

Can you provide more information on your car?

What are some specs? is it stock? => if not what modifications?

Do you have a wideband o2 sensor installed? => What are your AFR's?

I'd go through all of Kingtal0n's suggestions. Those steps are essentially the same for troubleshooting any vehicle.

Once you've gone through the basics (fuel, spark, and compression) you can usually narrow down your issue(s)


While you're at it, I would also:

Clean the maf, and add a dab of dielectric grease on the pigtail

replace your O2 sensor (you said redtop sr so skinny O2 sensor)
O2 sensor S13 SR20DET REDTOP: 22690-19P20 ('87 280ZX)

check your fuel injector seals / o-rings make
Upper injector o-ring
16618-53J00 7/95 and newer 300ZX TT (small/upper)

Lower injector o-ring
16618-10V05 7/95 and newer 300ZX TT (big/lower)

Just my

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Quiche2192

Thanks for the replies!

1) I did a pressure test like you said Kingtal0n and everything looked fine.

2) I haven't done a compression test yet so I guess that's next. You said not
to rent one? I guess I gotta buy one then.

5) I don't have a recirculating BOV unfortunately. Mine is vent to
atmosphere. I do have a long inlet maf tube.

17) I'll have to look into checking the fuel pressure. Kinda new to this so I
have a lot to learn still.

Hey EFITTZY,
the engine is stock and no wideband installed. It's on the way, as is the narrowband sensor. Yup, I'll go through the list.

I'll keep you updated.

Thanks again!

Quiche2192

Just thought I'd post an update. After all this time, turns out it was the Cam Angle Sensor. The old one had a crack in the plastic housing. Engine runs great now, except that at a certain speed (50 mph, but not sure cause no speedo) the engine leans out. Runs great otherwise, but doesn't go above about 50 mph

jr_ss

What is attached to you turbo inlet? If it’s the stock rubber boot, make sure the metal coil is inside. You could be sucking the turbo inlet closed.

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EFITTZY

Haha +1 for this! Especially since you said its a completely stock set up. Keep us posted

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jedi03

also verify what fuel pump you have and your fuel pressure regulator is good. hardwire your pump too

Quiche2192

The fuel pump is a walbro that the previous owner installed so I don't know the details. All I know is I'm getting 40 psi of fuel pressure with no load.

Did some more driving today with a speedometer app. Car sounds great, but it still cuts off at exactly 60 mph, consistently. No matter what rpm, what gear, at 60mph, it will cut and stay at 60.

I have an aftermarket intake with a silicone boot. It doesn't look like it could collapse.

Also read that it might be the transmission. Gonna check the fluid level and change it anyway since I already got redline for it.

BTW, the AFR Gauge shows a lean condition at 60 mph.

jedi03

maybe its the tune? any codes from the ecu?

Quiche2192

Ok so the ECU is throwing a code 21. Ignition components. I have new coilpacks and a new ignitor.

Also checked continuity on all wires and everything looks good as far as continuity goes. Gotta find out how to check for shorts though.

Oh and I'm using the stock 62 ECU. Idk if the previous owner maybe did something with the ECU though.

I'm waiting on a boost gauge to get here and I'll also check fuel pressure at load.

Really weird problem that I haven't found any info about online though...

Engine sounds just fine. Idles fine. It'll spin the tires just fine from a start. It just doesn't wanna go past 60 mph... Really leaning towards the speed sensor in the transmission. I'll check this weekend when I have time.

Thanks again for the input everyone!

jedi03

check ground on back of the head and also make sure the valve cover isn't leaking oil into the coil pack area...buddy had that happen, super intermittent and was just needing a new valve cover gasket...

Quiche2192

Ok got another update. I checked the speed sensor and the wiring over the weekend and found a point near the speed sensor where the wire was barely connected. I re crimped the wire and checked continuity. Everything looked good going from the sensor to the dash.

I was using the FSM troubleshooting guide which tells you to check the voltage coming from the speed sensor when you rotate it. But I didn't want to drain the transmission fluid yet, so I skipped that.

Until today. I decided to just drive the car with a multi meter connected to check the voltage coming from the sensor. It's busted for sure.

Here's the kicker. With the dash disconnected from the wire harness (in order to connect the multi meter to the pins), the car doesn't have the issue! A good indication that the speed sensor does have an influence on the ECU somehow; something I've been curious about the whole time. Or maybe my dash is messed up and sending bad signals to the ECU. But yeah I've actually been driving all night and enjoying the car

I accidentally ordered an s13 sensor last week only to find out that it will not give the correct speed indication. So I'm still running the busted sensor. I'm gonna order an s14 speed sensor and replace it, but in the mean time I can just drive it without the dash connected. I still get engine temp and fuel level from the other dash connectors. I don't have rpm and speed which I can deal with for now. I use the gps speedometer on my phone.

Thanks again for the help everyone!

jedi03

that's funny, prob grounded wire somewhere, i have my sr swapped fc running completely without a speed sensor, works great...