Carbretarder or Ignition problems?

[Smyrna720]

Ok, so I swapped a new motor in the truck. Said truck ran before the motor let go and then sat for about 4 months with the gas drained. I made sure to suck out the fuel from the tank and took the carb off and drained it. I then put everything back together and now I don't know what the fuck the problem is. I'm 99% sure it's the carb but I'm not ruling out the ignition system. Here is a video of how it's running. All the sparkplugs are sooty and black. The bottom of the intake manifold is wet when the carb is removed. I dunno. I've been through the carb since it needed a needle and seat and cleaned it thoroughly so I don't really know what to do next.

 

 

Also, the carb is a reman less than 2 years old, so I know it's not wore out. It's something else.

 

 

The only other thing is I want to make sure I hooked the control module up correctly, so here is a picture.

 

 

Lastly, all the wires ohm out good and they were on the truck when it was running. Spark for all cylinders is hot and blue. Timing has been checked and verified at a high idle. There are no vacuum leaks that I know of. Pintle has been removed from anti diesel solenoid. Also, fuel level is at the dot on the sight glass.

[datzenmike]

Looks like a feedback carb. The 8? pin connectors had continuity problems. Most usual was the wire breaking inside the insulation. The ECU uses sensor input to map the variable primary jet. When there is a failure it goes into 'limp home' mode and runs extra rich. You have the O2 sensor connected?

 

 

 

To check.... pull an intake and exhaust side plug and put in the ends of the wire, lay on a grounded valve cover and crank the motor. If both spark you're good.

[Smyrna720]

O2 sensor is connected. How would I go about checking the wires? I'm handy with a multimeter, but I need to know where these wires should have continuity to, where I can check my voltage drops and where they break at. I'll check the O2 sensor with my graphing multimeter tomorrow. Thanks for the heads up. I think a Weber is in my very near future, unless a non-feedback Hitachi turns up at a junkyard.

[datzenmike]

It's usually the leads from the round plug to the carb. It's thought the Nissan saved half a yen by running the wires tooo short. Every time you take the air filter housing off they get moved and it kinks them and eventually they break inside. Try wiggling the wires while it runs and see if the idle changes. Run a continuity between the plug pins and the carb body ends.

[Smyrna720]

Ok, I've done some testing and I believe I've come to a conclusion.

 

 

First, using this shematic, I tested the resistance of the variable primary jet solenoid. It measured about 40k ohms, which seemed good. No jumping around, solid reading. I would expect that since being an aftermarket reman carb, I would suspect that they would replace this part. Second, I checked the O2 sensor. Typically they should read around .5vac stoich on a DMM, or if you're on a scope, should cycle between 250mVAC and 750mVAC on a fuel injected app, not sure about a feedback carb. I was getting readings all the way up to 4.7vac. WTF? That tells me that it's going dead rich. Crazy rich. That also tells me that it's working. Cold, voltage started at .000vac and only climbed from there.

 

Sooooo, my best guess is that the variable jet is stuck, not allowing the solenoid to act on it. Fuck.

 

How would I go about pulling that out and cleaning it?

 

Anybody else got anything?

 

PS, for those that might have the same problem and are searching this thread, DMM = Digital Multimeter, VAC = Volts, alternating current, and mVAC is millivolts AC. Stoich is stoichiometric, or perfect air fuel ratio, 14.7 to 1.

[datzenmike]

Nice diagram. 720 World?

[Smyrna720]

Nope, you.

 

http://community.ratsun.net/topic/44964-terrible-to-no-idle/page__hl__idle

 

So, would you agree with my conclusion? I really have no idea how a variable jet works. My other thought would have been that the ECM isn't signaling the solenoid to move.

[Smyrna720]

Here's a link I found discussing mixture control solenoids.

 

http://www.teamswift.net/viewtopic.php?f=22&t=53897

 

I've got more tests to do.

[datzenmike]

The A/F solenoid is constantly opening and closing. The pulse rate is regulated by the ECU with help from a built in fuel map and feedback from an O2 sensor to keep it a stoichiometric. It operates in open loop (no O2 feedback) when motor is cold or during heavy or high speed operation.

[Smyrna720]

Well, I think I found the problem. I took the MCS out and it was full of crap. I could hardly open it. I could feel the thing clicking but it was hardly moving. I'm going to hit the junkyard tomorrow and see if I can pick one up, but I'm not holding my breath. I'm probably going to order a Weber tomorrow, unless one pops up for sale here or NICO.

[elmerfudpucker]

Nice diagram. 720 World?

Nope, you.

 

http://community.rat.../page__hl__idle

 

Now that be some funny shiznit! :thumbup:

[Smyrna720]

Oh yeah, the Weber should be here Thursday. I should have an update Thursday afternoon.

[Smyrna720]

Well, double fuck me Jesus on a pogo stick running sideways up a hill.

 

Needless to say, I got the Weber on. Also, it was not the problem. Well, I'm sure the old carb was a little bit of the problem, but I've got bigger issues.

 

I'll just start posting pictures and we'll go from there.

 

I couldn't get it to run right still with the Weber, so I broke down and bought a compression tester. Wish I woulda done that sooner.

 

Cylinder 1

 

 

2

 

Uh oh.

 

 

3

 

 

4

 

This was while cranking. It would instantly fall when I would let off the key.

 

 

So, I pulled the valve cover

 

I forgot to mention, I found this when I pulled the pan. We didn't know what it was at the time, but I know now. Timing chain tensioner.

 

 

Inside look at the tensioner.

 

 

Somebody has been in here before...

 

New chain.

 

 

Boogered up, so I know it's been messed with.

 

 

This is my OLD MOTOR ON THE STAND. This is what it should look like.

 

 

See how much taller it is?

 

 

Different chain.

 

 

 

So... Now I need to get the cam back in time. I suspect it's not where it should be. Anybody got any good ideas? I'm gonna tear into it and see what I can see.

 

Also, is this an interferance motor? I'm really hoping against hope that the valves aren't bent.

 

Oh, and if I get time, I'm going to put together a "How to install your Weber" post. I got a metric shit ton of pictures of that.

[Smyrna720]

Ok, change of plans. Comparing my old motor to the new one, I've concluded that the cam isn't out of time. Putting #1 on TDC compression, I noted that the cam gear and cam itself are in the same positions. Turning the engine over and checking valve lash, I've concluded that #4 exhaust is too tight, which is probably the cause of the low compression in #4.

 

So, WTF is up with #2?

[Smyrna720]

I'm betting every valve in this mother is bent. I pulled the schrader valve out of my compression tester and used compressed air to see where I was getting my leakage. Low and behold, it's coming out both intake and exhaust on #2, intake on #1 and I didn't bother checking the others. Looks like the head is coming off. Oh, and I just pulled the head on my core motor, both valves are bent on #1, the broken rod cylinder, and the thrust face for the cam is cracked.

 

Fuck.

 

 

[datzenmike]

If it is a new chain the chain guides weren't changed... that's what that black chunk is. It's off the top of the guide in the picture. Likely the chain wasn't changed and that's just normal neglect. As for bent valves... maybe. The only way is if the head gasket blew (it happens on the Z24s) someone lifted the head and turned the cam, then bolted it down with some valves at lift with the piston at TDC and torqued them down and bent them. Bad leaks like that could be just overheated and popped the valve seats loose.

[Smyrna720]

If it is a new chain the chain guides weren't changed... that's what that black chunk is. It's off the top of the guide in the picture. Likely the chain wasn't changed and that's just normal neglect. As for bent valves... maybe. The only way is if the head gasket blew (it happens on the Z24s) someone lifted the head and turned the cam, then bolted it down with some valves at lift with the piston at TDC and torqued them down and bent them. Bad leaks like that could be just overheated and popped the valve seats loose.

 

The chain looks awful new. It's got a bluish tint to it that the chain on the other motor doesn't. I'm not for sure that it's new though, and it doesn't show as much in the pictures.

 

As far as it getting that hot... holy shit, that's real hot. I've seen it done on an LT1 Camaro, and it got somewhere in the neighborhood of 260-280* before it quit. Same deal, head gasket shit the bed, no coolant, valve seats fell out and with no compression, it quit. I've got pictures of that somewhere...

 

Anyways, I guess we'll find out tomorrow.

 

What do you think about the head off my old motor? Wasted?

[datzenmike]

When steel is heated to around 500600F it turns blue. That chain guide rubber is missing. Maybe the chain heated from friction against it?

[Rays74]

Bummer this wasn't caught before dropping the ch$$se on that Weber........well, maybe replacing that feedback stocker isn't all bad...lol.

Sounds like you have some fun times ahead :)

[Smyrna720]

 

When steel is heated to around 500600F it turns blue. That chain guide rubber is missing. Maybe the chain heated from friction against it?

 

Nah, it's blued from the manufacturing process. That's how it's supposed to be. I checked out a factory Nissan replacement chain, and it looked like that. The factory original chain is bare white metal colored.

 

Bummer this wasn't caught before dropping the ch$$se on that Weber........well, maybe replacing that feedback stocker isn't all bad...lol.

Sounds like you have some fun times ahead :)

 

Yeah, tell me about it. I'm still glad I got the Weber... Don't tell my wife that though. ;)

[Smyrna720]

Diagnosis: Fucked.

 

I'll let the pictures do the talking.

 

Head off

 

 

Notice the new head gasket...

 

 

#2 piston was feeling frisky. Said to valve: Kiss me.

 

Intake

 

 

Exhaust

 

 

Same with #3

 

 

 

#2 exhaust

 

 

ALL of the intake valves look just like this.

 

 

Oh yeah, #2 intake valve guide

 

 

Broke the fuck off.

 

Intake # 4

 

 

Cracked.

[datzenmike]

Easy fix just replace the bent valves or get your old head. Some of those marks on the pistons are factory clearance notches. Only way they can hit the pistons is if the cam was timed wrong. By the way....

 

 

Your motor is on Bottom Dead Center. As long as you marked the chain and sprocket so it goes back the right way you should be ok. Someone put it together wrong and caused this.

 

Before installing any head be sure that the #2 OR #3 valves are both barely open while the other ones are both closed. As you can see, the middle pistons are at TDC so one of them must be on the compression stroke the other on the exhaust. Pick one and stay with it. Assume the #2 is at TDC compression stroke. Both #2 valves must be closed and both #2 cam lobes downward with the exhaust at 8 o'clock and the intake at 4 o'clock as viewed from the front.

 

Fit the head and be sure that it sits flat on the block and nothing (like a valve) is holding it up. If there are, then you don't have the cam in the proper position. Remember the #2 valves must be closed and the #3 valves both just barely off their seats. Install the head bolts but don't torque down yet.

 

Because your motor is not at TDC the valve timing cannot be correctly assured without doubt. It should be close though. With the timing chain and sprocket replaced, turn the motor over and line up the TDC notch on the crank pulley with the timing scale. Be sure to turn the motor up to the timing mark in a clockwise direction only. If you over shoot back well up and try again as many times as needed to get it right.

 

Now look through the top hole on the cam sprocket and down in behind at the notch in it. The notch should be under or just to the right of the vertical casting mark between the two rocker arm towers.

 

 

Very faint vertical casting line.

 

 

 

Blurred U shaped notch in bottom fore ground. Is just barely to the right of the vertical casting line. Directly below is fine to but not to the left. This cam is perfectly aligned.

 

As long as you are close it's now safe to torque the head gasket down but you will need to check the final cam timing with the gasket crushed.

.

[Smyrna720]

I've turned it since the head has been off to clean the pistons. I'm in the process right now of taking the timing cover off. I'm going to go ahead and replace the guides since they're foobar'd. Did you see the crack in my old head? I wasn't sure if the crack in the cam thrust face was a big deal or not. Also, I'm going to go up to the junkyard and see if they'll exchange me a head.

[datzenmike]

Ah it's all good. Crack won't hurt. Won't hurt if you replace either.

[Smyrna720]

Got a head. Getting gaskets now.