high idle, hesitation when cold, dead spots when hot

[gogg]

Well it goes like this, my friend had a DOHC in his car, got good fuel milage, didn't burn oil, only problems were that it wouldn't startup without giving it gas, it also had slight hesitation problems and high idle. He put in a walbro fuel pump, still wouldn't start without gas, but the hesitation seemed to go away.

<fast forward>

He's doing an sr20 swap, I get the engine. Same problems, except I'm getting major hesitation. Pull the plugs, they're white, so I get a walbro. Put it in. It's now present day. The car starts fine, It might take 5-6 cranks in the morning though. It idles at 900 when its first started then heads up to 1200 and moves back and forth from 1200 to 1300. I still get alot of hesitation when the engine is cold, like I'll put it in 2nd and I give it the usual amount of gas but it's like I'm giving it alot less. Once the engine warms up I usually hit two dead spots around 2500 and 2800 rpm.

So when it comes down to it it could be something like a bad spark plug, clogged injectors, or bad o2 sensor, but that wouldn't really explain the high idle, that would be along the lines of throttle position sensor (tps) or auxilary air control (aac) valve.

Whats been done:new walbro fuel pumpnew 300zx fuel filternew coolent temp sensor

also note there is a very slight chance the spark plug wires might not be making good contact, but I've checked 'em out and I don't think this is causing any problems.

I've tryed to explain everything accuratly, things in () are keywords for searches.

Thanks in advance to anyone who can help!

[InsanityInc]

You're saying that both motors have the same problems in the same chassis with all different parts on the engine? That lets you rule out pretty much everything... Could be an exhaust leak, or somewhat clogged fuel lines. That's really all I can think of outside of the engine that would cause it.

[navysnail]

i would go ahead and do a full tuneup, it sounds like there may be more then one problem

[gogg]

You're saying that both motors have the same problems in the same chassis with all different parts on the engine?

???? no....

the motor had the same problems in both cars...

[InsanityInc]

Oh, the way you worded it, it sounded like you were saying you got the SR20.

[s13sr20chris]

try spraying around the intake manifold with carb cleaner and see if the idle pics up some more. you may have intake manifold leak. they are quite common on the ka24de.

[gogg]

where are common areas that the intake manifold leaks?

[s13sr20chris]

cyl four is typical on altimas and cyl 2 is the only one i have seen on a 240sx. it will leak at the gasket right between the manifold and the head.

[gogg]

Update time:

Seafoamed the fuel system, still have the dead spots. I'm thinking the seafoam would have unclogged the injectors or lines if they were clogged.

Also checked for intake manifold leaks, pretty sure I don't have one. But when I was doing that I noticed that at cold start it takes about 4 cranks for the car to start if I don't let the walbro pump have enough time to "prime" the car (just stick in the key and crank) and the car idles at 1500 then I go WOT and it goes down to 1300.

And finally a better explaination of the dead spots, they are more noticable when the engine is cold. When I shift into 2nd or 3rd (more noticable in 2nd) and re-apply the accelarator it's like the throttle takes about half a second to react (not as bad sometimes). I also notice when the car would be around 2500-3000 upon shifting the same issue happens (when warm, just not as bad, but noticable). So all in all there's "dead spots" around 2500-3000 rpm. I'm thinking this could be an issue with the TPS. Thanks.

[gogg]

Another update: I checked the EGR, it works, but the rubber elbow vacuum hose was busted, so I replaced ... I still have all the same problems.

I'm also getting code 14 on the ecu diagnostic test, which is vehicle speed sensor.

Drove it again when it sat overnight, the hesitation is pretty bad at anything below 3000 rpm till it gets warmer, then it just has the dead spots.
Modified by gogg at 1:39 PM 9/26/2004

[s13sr20chris]

the issues when warmed up could be a funky o2 sensor. when you go wot the ecm goes open loop and it could take a fraction of a sec to get to the right a/f after running rich on closed loop(from bad o2). thats a possibility. wot is a ok right? that just makes is seem more like an o2 but could be tps as well. do you have a way to monitor maf, o2, and other parameters while the dead spots are happening?

[gogg]

do you have a way to monitor maf, o2, and other parameters while the dead spots are happening?

the engine would have to be under load...so uh i dunno.....what should my plan of action be?

[s13sr20chris]

well, this is where i would put consult on it and go for a ride. you dont have that luxury but if you have long leads for your meter and some t-pins you can backprobe the connectors and drive with the leads going through the window. lot of work i know. i tell you what. why dont you try driving around with the o2 sensor unplugged. after that maybe try the tps unplugged.

[gogg]

Update: Seafoamed intake, replaced spark plugs, and o2 sensor, cleaned up the wires.

still nothing

(could this be a result of the ditributer, rotor, or cap?)

I did a test on my IAVC-AAC and it said it wasn't working entirely correct.

The test was pinching the hose when the car was warm, the rpms went down about 100, showing the valve is open when it shouldn't be right?

Sprayed seafoam into the hose, hoping that won't mess anything up and maybe it'll fix it, although it hasnt done anything so far.

[s13sr20chris]

iacv aac should not cause this prob. it could be a dist issue. they can be quite tricky to diagnose. you may be stuck with the trial and error parts swapping method. i dont guess you live in pa do you? theres a guy up there who needs to swap some stuff.

[gogg]

A mechanic said my distributor was clicking when he used his stethscope on it, and that it might go out soon... dunno if he was right or not.

[gogg]

Ok, if theres one thing I want to fix, if I could choose from any of the problems it's this: when the engine is cold and I push the accelarator it takes a second to a couple of seconds for the engine to "react".

Is that a TPS malfuction? If not, wtf is it?

Thanks!

[s13sr20chris]

i think that is just nissans cold run strategy. most older nissans(including mine) do it. i would attribute it to a rich condition. maybe with an safcII or hks afr you could tune it out.

[gogg]

Hmm, usually in the morning when I just start up the car and start driving, the car surges, like I'm letting off the gas and then getting back on it. This only lasts about a minute though.

[NateDogg]

Thats what my car would do after the Walbro blew out the stock fpr. Check your fuel pressure. It should be 34psi at idle with the vacuum hose to fpr connected.

[gogg]

What did you replace it with? Another stock? or aftermarket?