# 94 hardbody misses, but only when hot.



## endofmyrope (Oct 13, 2011)

Alright, as you can see by my user name, I am at the end of my rope with this truck. I know nothing about nissans, so if you need any specifics let me know. 94 model 2400 I'll do my best to describe what it is doing and what has been done.

When the truck was first brought to me, it had a dead miss all the time. Narrowed the problem to a failed fuel injector. Replaced injector and all was fixed, or so I thought. 

If you start the truck and the engine is at ambient temp it runs great. I have driven it 30+ miles without an issue UNTIL you shut the engine off and let it sit for a short period of time. After that short period of time when you start the truck the engine misses, hesitates and has low power. I have driven it for a few miles like this and it showed no signs of improving. So I get pissed and let it sit. Start it up the next day after sitting all night and she runs like new. Something is failing when the engine is hot, but what would not effect it until the engine has been shut off for a short period of time?

List that has been done to the truck,
New plugs, wires, cap and rotor
4 used injectors
1 used coolant temp sensor
1 used fuel pressure regulator
checked and adjusted timing
checked fault codes, has a code 14 v.s.s. speedo does not work


Anyone have any ideas???


thanks!


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## smj999smj (Jan 1, 2006)

Well, first thing I would do is test the fuel pressure and, more importantly, check for fuel pressure leakdown. If one of those used injectors is leaking down after you shut it off, it can cause a misfire. It's also possible that you may need a distributor. It would be nice to be able to observe the spark patterns on an oscilloscope.


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## Scott_T (May 15, 2011)

just a wild guess but I'd check the EGR


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## endofmyrope (Oct 13, 2011)

How do you check the fuel pressure? I see no ports to check it unless I am missing the obvious. Its getting more and more to were I wish I had access to an oscilloscope. If I had one I'd take on more pre 96 model year work.

Scott_t. Ill look into the egr, just doesnt make sense that it would be open after sitting for a time...

Thanks for the help guys!


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## smj999smj (Jan 1, 2006)

The fuel pressure is tested with a "T" adapter mounted between the top of the fuel filter and the fuel filter hose.


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## rogoman (Dec 16, 2004)

The fuel pressure regulator may be bad. Like SMJ said, you'll need to tee-in a tempoarary fuel pressure gauge at the output side of the fuel filter. The readings at idle should be as follows:
- with vacuum hose connected to the fuel pressure regulator: 33 psi
- with vacuum hose disconnected from the fuel pressure regulator: 43 psi


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## endofmyrope (Oct 13, 2011)

Ok, I will see what I can rig up as soon as I get a minute. I already swapped the regulator, but who knows if it is any good. The owner has a spare engine with all the sensors, so I grabbed what I thought might cure what ills it. I'll post what the pressures are as soon as I check it.

thanks.


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## endofmyrope (Oct 13, 2011)

Checked fuel pressure. 33 with regulator and 45 without regulator, even when truck was missing at running like crap. I even tried unplugging the temp sensors to fool the ecm into cold start (assuming that is default for the ecm) and it still ran like crap. Any tests that can be done on the distributor? I thought I had another one but turns out it was damaged so thats a no go. 

Sorry it took so long to post this. Just got to it the other day and have been super busy!


Thanks again guys!


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## SPEEDO (Jun 9, 2003)

sounds like its the dizzy... it will get to a point were it (the engine) will shut down when it gets hot
1st check the cap/rotor for any arching


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## saudade (Apr 10, 2010)

Try driving it farther than 30 miles if you can. If it runs fine when cold, will it suddenly switch while still running? Or do you need to shut it off first, wait a bit then restart?

Engine bay temps can rise higher after shutting off due to heat soak and the lack of cooling air. For example, there's a service bulletin on Jeeps that develop a misfire due to fuel vaporization within the #3 injector due to the heat soak (only after shutdown). This fix requires a insulating boot around the affected injector(s). Not saying this is your problem.


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## endofmyrope (Oct 13, 2011)

saudade, It seems to run fine until its been shut off. I too thought about the engine bay temps rising, but I have duplicated the problem in the driveway with the hood open on a cool day. Not saying that it still can't be heat related because it obviously is, but I figured with the hood open it would at least dissipate the heat much faster.

I'll have to get a day and go for a drive in it, Not exactly convenient to drive something around that may or may not leave you 30+ miles from home. 

Wish I had a good test dizzy, the one from the other engine I have is bent from the wreck....damn it.:balls:


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## endofmyrope (Oct 13, 2011)

You do have to wait about 5 minutes of being shut off. If you shut it off and restart it right away it seems to be ok.


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## rogoman (Dec 16, 2004)

It may be worthwhile checking the EVAP canister system. Also check for vacuum leaks in the intake system; use a vacuum gauge.


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## saudade (Apr 10, 2010)

Hmmm.... I'm still leaning towards an injector issue.

While it's heated up and missing, can you pull of the injector connectors? If you can, do so 1 at a time. The miss will get worse for the working cylinders and not change for the one that's "missing". 

So pull the connector off injector #1 and note any change in idle and smoothness. Then put it back on and note any difference again. If #1's OK, it should get rougher when disconnected and improve connected.

Then try #2-4 and see if you can identify the "bad cylinder". Once you do, pull the spark plug and have a look to see if it's fouled.

I know you replaced the injectors, but being used, you may still have a bad one.


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