# 91 nissan pickup stumbling past 2k rpm ??



## -d21- (Jul 4, 2009)

91 Nissan Pickup
2.4L 4cyl
KA24E Engine @ 138k KM on engine and body

Alright, I am getting brain-fckd by my truck right now. Here's the big picture .. (long post-beware!)

A couple'ish years ago, my timing chain ripped through my side rail and tore a hole into my timing cover ( right into the water jacket ) resulting in a giant Oil/water/coolant orgy. No good. I was strapped for cash then, so fixing it wasn't really gonna happen.

A couple months ago (just under 2 years after the truck prob occured), I decided to fix this shit up. So.... I stripped the engine down to the block to do a semi-rebuild. I replaced the

- timing chain/tensioner/rail, both sprockets, new front seal
- I got the timing cover welded where the hole was torn,
- replaced the head gasket and all gaskets that I needed for rebuild,
- New water pump

As for the rest of the parts, they were thouroughly cleaned, re-lubed and re-assembled. I have the engine back together now .. and after getting a good portion of fine-tuning out of the way ... I am completely SNAGGED on this one problem...

I got my engine idling at about 650, but whenever I give'r accel to go above 2000 rpm... VWOOMBLUAGH ... it stumbles ... comes up ... stumbles down ect ect. Ive seen many other online cases like this, where some of them were a quick fix ( like BPT or EGR valve was stuck or just needed to be cleaned). Not my case ... I have done a compression / fuel pressure / and vacuum test and to no avail. All seem to check out.

Ive also taken my whole egr system out examined it and cleaned it, as well as blocking it off completely and still no fix.

As far as codes ... I got some MAF and air temp sensor codes, but I was able to clear all that up and now im getting the good 'ol '55 SYSTEM OK'.
These codes were from the truck ECU and I also scoped it.

One thing that just aint right, is how lean my truck is running. It's obviously thinking its too rich when i accelerate because it decides to not inject ENOUGH gas past 2000rpm. Right now my main focus is the MAF and possible o2 sensor, even though i'm getting no codes.

Anyway, sorry for the long post but the more info the better diagnosis, right?
if ANYBODY has had similar problems and have found a fix for them (even if its a completely unexpected, stupid fix) I would really appreciate any advice/info/solutions ect.

Thanks !


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## zanegrey (Dec 5, 2005)

the first thing is to put the engine at number one position and check and recheck the oil pump timing..

if you are getting a 55 ..the ecm is good and none of the sensors are bad..

oil pump timing or crap in the fuel tank...


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## -d21- (Jul 4, 2009)

if my chain and dizzy are both timed, wouldn't that mean my oil pump marker is lined up? 
i'll recheck it regardless though. 

Another thing to add, as it stumbles just when you get past 2k rpm... If i really give'r on the gas pedal and get it to over 3k rpm the stumbling stops and it revs like a beast.


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## zanegrey (Dec 5, 2005)

check you fuel supply and go over the vacumn system..


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## -d21- (Jul 4, 2009)

Well Ive decided to Remove the timing cover just to double check oil pump marking w/ dizzy spindle ... check the pcv valve ... and remove the driver side chain rail (which i have learnt is supposedly more of a pain in the ass than anything and that there was actually a recall on them by nissan back in the day)... I'll post anything interesting, including whether or not the side rail is the cause to the clanky engine noise I have also been experiencing. As for the post 2k rpm stumbling, I'm not really expecting any of this to be a solution, but ya never know.


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## -d21- (Jul 4, 2009)

Oi. frusterating ...

Removed timing cover, oil pump and spindle ... checked, Reinstalled timing pump double checking marks lined up ... N.1 @ TDC dizzy at N.1 everything good. Re-assembled ... Still stumbles, Still 'knocks' at top end.. Pretty sure the knocking noise is the hydraulic Rockers and not valves. But damn, this is just draggin on. 

If once again, if anyone has had this stumbling and has fixed it, plz throw some advice my way. 

Also, i've heard you can reduce rocker noise by using the air-bleed on the front side of the intake manifold ... if anyone knows anything bout that then lemme know. 
thnx.


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## -d21- (Jul 4, 2009)

ok, one question to anyone who has the answer. 

For Hydraulic Rocker arms, when all the valves are closed for a cyclinder, should there be ANY clearance between the cam lobe and arm? As in, if i were to put a feeler gauge between the lobe and lifter when all valves are closed, should it be able to fit in there? 

thnx again.


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## zanegrey (Dec 5, 2005)

there will be a very small gap...

update us please...


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## nissan4x4.27 (Jul 8, 2009)

my 97 hardbody is doing the same thing. but once you start driving it thats when it has problems. i have to get a fuel filter for it for sure but when i rev it up on ideal it back fires from the throttle body anyone know.


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## zanegrey (Dec 5, 2005)

post up your mileage


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## nissan4x4.27 (Jul 8, 2009)

it has 388 063 on a semi rebuild


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## zanegrey (Dec 5, 2005)

there is a vacumn operated dashpot on the firewall side and to the rear of the intake mani..

this dash pot operated the four butterflies in the meeting point of the mani and head ..

check that dash pot and its vacumn lines...


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## nissan4x4.27 (Jul 8, 2009)

that will cause the back fire in the throttle body. and friend said i was getting to much gas is why its back firing


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## zanegrey (Dec 5, 2005)

or it is out of time ...

did you check the dash pot and its operation ?


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## nissan4x4.27 (Jul 8, 2009)

how do i check the dash pot?


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## nissan4x4.27 (Jul 8, 2009)

and what im i looking for when i running it


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## nissan4x4.27 (Jul 8, 2009)

anyone know what i need to be looking for???


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## zanegrey (Dec 5, 2005)

a vacumn operated dash pot is a mechanical switch..

it moves in a pre determined motion dictated by vacumn pressure..


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## nissan4x4.27 (Jul 8, 2009)

thanks anyways i got it figured out after stuff broke trying to find out what i was doing


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## zanegrey (Dec 5, 2005)

regale us ...


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## nissan4x4.27 (Jul 8, 2009)

regale ? what do u mean


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