'92 SE with 220k Miles - Full upper end rebuild - Black smoke and power stutter over 2500k rpms

[Bozer1991]

I just finished rebuilding the truck and can't get it to run right. Starts up, idles fine, temp and fuel good - but it pukes black smoke and has no power over 2500k rpms.  I have chased every possible fix, but no luck...  I need help!  Here is what I've done:

 

Resurfaced Heads and Valve Job

New Head Gaskets

New Crank and Camshaft seals

New gasket set from Fel Pro all around

New Timing belt and tensioner

New Water pump

New Thermostat

New Alternator

New Distributor, rotor, wires and plug - all Nissan OEM

New PCV and O2 sensor

New Vacuum lines throughout

EGR works, piping cleaned

New fuel and air filters

New Coolant Temp switch

Cleaned throttle body

Fresh Oil and Filter

 

Please share any ideas on how I can get her going.  Thank you!

[adamzan]

Have you verified the timing is accurate as well, check the mass airflow sensor, common issue to have the wiring at the connector be flaky.

[Bozer1991]

Yes, timing is spot on 15deg BTDC. I also pulled MAF sensor, cleaned it thoroughly and checked wiring.  I ran a fresh ground over the front plenum bolt. No luck.

 

I ran ecu codes and got #35 and #45.  Both the coolant temp sensor and fuel injectors are new, so I figured vacuum leak?  

 

Gave up chasing it yesterday and pulled the plenum back off.  I am going to replace the Fuel Pressure Regulator and make 100% SURE all injectors are seated right.

 

She's fighting me, but I'm not giving up yet

[Slartibartfast]

45 is injector leak. The computer does not have a sensor for this. My understanding is that the computer throws this code if the mixture is rich and it can't do anything about it. Check your spark plugs. If only one spark plug is dark, that suggests an injector leak on that cylinder. If all six are dark, something else is wrong. If the injectors weren't seated right, I'd expect vacuum leaks (lean), not fuel leaks (rich). A bad fuel pressure reg (too much pressure or puking gas up the vac line to the plenum) would make sense. I know you've done the coolant temp and oxygen sensors, but I would double check those, and the condition of their wiring (both the harness and the connectors, including the connectors on the valve cover). I had intermittent trouble with my MAF plug for years, and it looked perfectly fine inside. But if felt loose, and wiggling it tended to clear up the problem for a while.

 

35 is EGR temp sensor, not coolant. I don't see that sensor listed as important to the fuel injection (or even the operation of the EGR system!), so I doubt it's causing your problem. AFAIK it's just there to complain if it doesn't see heat when the EGR is supposed to be operating. Maybe the exhaust temp is low because of the rich condition, and that's enough to trigger the code? I would focus on the other code for now, see if this one clears up when you get the rich condition sorted out.

 

19 hours ago, Bozer1991 said:

I ran a fresh ground over the front plenum bolt.

 

I once tried that on my '93, and it did not like it. My '95 parts car came with a short MAF extension harness with a separate ground lead, so I swapped it into mine, because why not. I have never heard mine run so poorly. I don't know if it was rich or lean, but whatever it was, it was not happy. It ran fine again with the ground disconnected. I have no idea why, or if this is typical. But if yours ran fine before the rebuild, without that added ground, I would disconnect it before doing further testing, on the off chance it's adding another issue on top of the one you're already chasing.

[Bozer1991]

Interesting..  I think it did run worse after that ground was added.  OK, great intel, thank you @Slartibartfast. 

 

I have the Plenum and Fuel Rail back off now and will install new Fuel Pressure Regulator today. I am going to give the wiring harness a thorough assessment while I have access.  MAF is on the other harness, so will check that too.

 

I'll share results later

[Bozer1991]

Well, s$%#.  Put it all back together after adding a new oem fuel pressure regulator and it runs worse than before.  Black smoke, weak power and stalls out. 

 

I cleaned and added dielectric grease to every connector, checked fuel rail integrity and all looks good.

 

The MAF seems to work because when I pull it off while running, the engine dies.  Wiring and connector look good.  It had a added wiring harness with a separate ground wire, which I removed. No change.

 

Could it be an exhaust blockage?  The brand new O2 sensor is black, which i expected after all the smoke.

 

Plugs all looked black, but dry.

 

Vacuum lines all new.

 

New air filter and I cleaned out the filter box.

 

I don't know.  Getting pretty frustrated!

[Slartibartfast]

Yeah, I'm sure it's frustrating as hell. One of those moments where it would really help if these ECUs could show us live sensor data!

 

Running worse over time is likely just the plugs starting to foul. All six fouling the same suggests it's not an injector issue. The new fuel pressure regulator not helping suggests the excess fuel isn't coming up the vacuum line from a bad reg. So either something is forcing more fuel through the injectors than the computer intends, or the computer's getting bad info that's causing it to inject more fuel than it should.

 

Check that the fuel return line isn't pinched or otherwise blocked. Maybe a mud wasp got in there while you had it torn apart? If you can't blow through the return line, then it doesn't matter if the regulator is working, because the excess fuel can't leave the rail. I would also check that the fuel supply and return are plumbed the right way around, though I don't think it would run at all if you had those crossed up.

 

If the fuel lines are OK, try running it with the coolant temp sensor disconnected. If the computer knows that the temp sensor isn't working, it'll guess the engine temperature based on how long it's been running. If this makes it run better than it did with the sensor hooked up, check the resistance of the sensor, and the wiring between the sensor and the computer. (The service manual's troubleshooting for the temp sensor code should tell you which pins to probe for this.) If that doesn't help, plug the temp sensor back in and try the same with the MAF. Again, if it runs better on guesses than it does on sensor data, check everything in that circuit. I know it stalled when you tried unplugging the MAF while it was running, but that may be different it you start it with no MAF vs if it loses connection while running.

 

Check that it codes for the temp sensor and MAF when they're unhooked. If the computer doesn't notice that a sensor is unplugged, then something ain't right with either the harness (current leakage makes the computer think it's seeing sensor data?) or the computer. I would also disconnect the battery for a bit before/after each test to clear any previous codes and self-learning.

 

I would not expect a blocked exhaust to cause a rich condition.

[Bozer1991]

OK, thank you for the feedback.  I'll start chipping away at these and keep you posted.

 

*I got it running as good as it ever did again last night by adding back the extra MAF wire loom with additional ground wire. Clean ground goes to the AC bolt close by. Now it runs ok below 2800 rpms, but bogs down above.  No more stalling and less black smoke.

 

The o2 sensor and plugs are pretty fouled, so I need to clean or replace again.

[Bozer1991]

I bought a set of injectors off eBay.  Now I'm wondering if they are garbage.  I bet they are, based on the low cost for a set of 6.  

[Slartibartfast]

Is that what's in it now? I think you'd be the third person on here who's tried those and had issues.

[adamzan]

Those ebay injectors have caused a lot of problems for a few people. But since it got better after fiddling with the MAF, that would be suspect to me as well, especially the rpm dependant issue. You don't have a spare MAF laying around that you could try, do you?

[gamellott]

I doubt that it would be the coolant temperature sensor. On my rig, a previous owner broke that connector and it was disconnected for quite some time before I discovered it. That connector being disconnected did NOT cause any issues near as bad as what you are experiencing.

 

Isn't the limp mode setpoint around 2800 rpm? 

[Bozer1991]

I bought a new set of reman'd injectors, best I could find online. Much more expensive, but worth it at this point. They arrive tomorrow and ill install asap.

 

The MAF ground wire repair only got me marginally better.  Still runs poorly.

 

Im leaning in to this faulty injector theory. I hope it works, I'm out of options!

 

Will report tomorrow.

 

Thx for all the input 

[Bozer1991]

I bought a new set of reman'd injectors, best I could find online. Much more expensive, but worth it at this point. They arrive tomorrow and ill install asap.

 

The MAF ground wire repair only got me marginally better.  Still runs poorly.

 

Im leaning in to this faulty injector theory. I hope it works, I'm out of options!

 

Will report tomorrow.

 

Thx for all the input 

[Bozer1991]

Well, the black smoke is gone.  But, it was replaced by white smoke! Tons of it. There is no way I have a blown head gasket. Resurfaced heads from machine shop, new gaskets, everything torqued to spec (oem torque sequence followed, etc..). WTF.  This truck is cursed. I'll do a compression test tomorrow. Unbelievable. 

[Bozer1991]

Somehow coolant is getting in the system. I've run it for about an hour and the white smoke is thick, no change. It runs well otherwise,  temp is good. 

 

Im confused.. how could a coolant leak start after pulling the plenum only? I did find a coolant leak out of the host that runs from the throttle body back to to the inlet to the right of the PCV. What s that?

[Bozer1991]

Solid compression across the board:

 

#1 - 190

#2 - 180

#3 - 180

#4 - 187

#5 - 185

#6 - 180

 

Plug #6 is fouled a bit already.  Coolant must be in there, but I can't figure out why.  I guess I'll drain oil and start over with a fresh batch.

[adamzan]

Could be bad intake manifold gasket?

[Bozer1991]

I replaced the intake manifold gaskets. Maybe they aren't sealing right. Ill have to take it apart again to find out.

 

I guess it could be a crack in the block, but I seriously doubt it.

 

Possible that a bunch of coolant is in the exhaust system and that is causing all the white smoke?

 

I am getting a coolant leak where the small hose comes out of rear drivers side of plenum right next to PCV. I have cranked down on hose clamp, but it's breaking through. 

 

Thx for the input.  Good news is I have mastered the #6 plug removal and install. I can swap that thing in/out by feel in 5 mins!

[Slartibartfast]

Sounds like the leaky hose you're looking at is the one from the throttle body to one of the idle air valves. Both have coolant plumbed through them to keep them from icing up. Could be the end of the hose has split. Could be it's not the right hose. 

 

Given this started when you had the plenum off, I'm wondering if you've switched a couple of lines, and accidentally plumbed vacuum to coolant, so it's sucking coolant right into the plenum. I don't know if there's an easy way to do that on a VG30, but a friend of mine managed it on an Alfa Romeo once. If you want I can get a picture of the plumbing on mine to compare.

 

The lower intake manifold gasket would be my next guess, though it's odd that it would choose now to let go. Might catch it with a cooling system pressure tester. Pump it up, pull the plenum and plugs, and see which runner or cylinder fills with coolant.

 

I have seen a cylinder with a bad head gasket pass a compression test, but that one was just barely leaking. If yours was leaking enough to make the new-pope-smoke, I would not expect the failure to be sneaky.

 

I've heard of oil in the exhaust smoking for a while after the engine is fixed, but I would expect coolant residue to clear up quicker. I had an old Ford make a hell of a smoke show when I warmed it up, but that wasn't oil or coolant--the muffler was chock full of mouse house. It smelled about how you'd expect, and it didn't clear up until I cut the muffler off.

[Bozer1991]

I've checked the hoses thoroughly, so no mixup on coolant/vacuum lines.  

 

Yes, I'm referring to the hose from throttle body to IAC and I was unable to find a new replacement, so pulled a junk yard backup. It has 4 bends in it, so tough to replace with an aftermarket hose.

 

F it. Im pulling it apart again to get eyes on the intake manifold gasket.

[Slartibartfast]

Guess that would've been too simple. I've heard you can bend lines with a spring and heat, haven't had a chance to try it myself yet. Might be worth a shot if the line is cracked. Good luck with the lower, hopefully the failure is obvious when you find it.

[adamzan]

8 minutes ago, Slartibartfast said:

Guess that would've been too simple. I've heard you can bend lines with a spring and heat, haven't had a chance to try it myself yet. Might be worth a shot if the line is cracked. Good luck with the lower, hopefully the failure is obvious when you find it.

That's pretty much our only option for a lot of the hoses now, like the pcv ones. Either run a massive loop of hose or use those spring host bender things the parts stores sell. hose bender springs | McMaster-Carr

[Bozer1991]

No smoking gun, unfortunately.  The intake manifold gasket looks good, basically new.  Makes me wonder if factory torque specs are enough?  The gasket barely has an impression from Block/Manifold.  Maybe I just torque the crap out of it and try this all over again...  These gaskets are all uniform surface, where the old ones had more of a built-up rubber ring around the coolant and air ports.  Maybe Fel Pro is the wrong call after all?

 

*When I pulled manifold a bunch of coolant spilled into #5, this happens because my driveway is on an incline and #5 and #6 are at the low end.  There is also coolant trapped in the heads back there, because of the tilt.  Wondering if this, somehow is contributing to my issue? I will spend an hour making sure no remaining coolant is in the cylinders, heads, or anywhere else.

 

I am waiting on new gaskets and when they are here, I'll get it all back together again and see where we are.

[Slartibartfast]

3 hours ago, Bozer1991 said:

These gaskets are all uniform surface, where the old ones had more of a built-up rubber ring around the coolant and air ports.

 

I think you may have the wrong gaskets. VG30 intake gaskets have the rubber rings around the ports. VG33 gaskets are thin stamped steel. (The VG33 intake is slightly wider for some reason.) Aftermarket may be built a little different, but they should be the same thickness as the ones you originally removed. I made the same mistake on mine once, because Rockauto listed the wrong parts and I didn't know any better, and I got hellacious vacuum leaks, probably because the intake got lower but the EGR tube didn't get shorter, so it was holding the plenum up at an angle. Did the bolt that holds the middle of the upper timing cover to the lower intake not line up properly? That was my first indication that I had the wrong parts. Well, that and the EGR tube not wanting to line up.

Edited Friday at 12:04 AM by Slartibartfast