Hardbody driveability issues, hesitation, light bucking

[HRH]

EDIT: FIXED! Post #25

 

So here's the thing, the D21 made it to Canby and back, she's been running great, getting consistent 21-22 mpg. Recently however, she's begun to have a few issues.

 

Basically it's been a slight oscillation/bucking right at tip-in, light load, mostly at 2000 rpm or close to it. It's fairly annoying as it's almost non-existent, but it's there. When I first noticed it, the stick shift moved back and forth, and I could feel a slight vibration in the drivetrain, as if the motor was lugging to the point of kicking back. But it was in a more controlled manner.

 

I thought it was the tires/road surface/generally the rough ride of a truck, that's how small it was. After a while though, I found it wouldn't do it all the time, only part of the time. However, when it was possible to get it to do it, it was repeatable, usually right after tip-in, light load in 3rd or 4th gear around 2000 rpm. Granted that's low, but here's something, it doesn't seem to do it when the motor is lugged at 1500 rpm, so it has enough beans to carry the weight.

 

One thing the truck has done since I got it, was have an issue with hot starting. After the truck has been shut off for usually longer than a half hour or so, she won't start right back up if you get in, turn the key and go. It'll snort, gasp, and die. I've been ignoring this since if you turn the key on and let it prime for 4 seconds, it'll start right up.

 

So today, I finally hooked up the fuel pressure gauge I got from Jegs to it. During the first test, initial pressure was reached at 43 psi, pump kicked off after priming like it's supposed to, and then the pressure started to drop (as observed on the videos I shot while testing) immediately, but it still fired right up. While it was running, tested the fuel pressure regulator to exhausting, it's definitely fine. However, when I turned it off, pressure dropped to "0" immediately.

 

Fast forward to this afternoon where I repeated testing. Let it sit for an hour after the first session, and went to replicate the hot start issue. Sure enough, she cranks over for like 10 seconds trying to start, fuel pressure at "0" until finally shooting up to 32, then starting. After that, everything is fine. Now here's the funny part. After shut off, fuel pressure was held like it's supposed to be. Did this a few more times, and pressure was still holding a few hours after.

 

So what would make the fuel pressure drop? It's technically a separate issue from the hesitation/bucking issue, but I can't help but think the two are related somehow.

 

I changed the TPS a few days ago, set that, reset initial idle, reset TPS idle with IAC valve unplugged, etc. etc. Thing idles great, runs well. It's completely driveable, but the hesitation is still unpredictable and I'm dreading the day it leaves me on the road side, which is why I'm trying to find it now, as minor as it may be.

 

So far, I've exhausted the reading of the FSM and have found some interesting things. One mentions hesitation during running regarding the purge valve on the vacuum canister/carbon canister thing. Mentions removing, plugging the vacuum line and running to see if hesitation is gone. That I'll try tomorrow.

 

Aside from that, I've tested the IAC, it appears to be fine, the TPS is new, it's set correctly and fine. The truck idles well and responds well, if you romp the throttle she shits and gets.

 

My thought now is leaning toward the fuel system somehow. I haven't been able to run the truck and get a pressure gauge reading of the hesitation issue, in which I expect to see a fuel pressure fluctuation. Or not, not sure. But since I don't have a consult it means taking off the hood, duct taping the camera in the engine bay and driving around trying to replicate the issue. I figure I should be able to diagnose it without doing that.

 

So aside from the fuel pump there is a fuel check valve which also has a rollover valve built into it. It's a ball type like in a shop vac, so it shuts off if at 90 degrees or 180 degrees, but isn't like the Ford type you have to reset to get fuel flowing again. There is a separate portion of that unit though that is just a check valve and I don't know if it's function is to hold line pressure or somehow it functions differently.

 

Anyone have any bright ideas here? I love fuel injection but I'm damn near ready to throw a Weber on her and call it good! ;)

[Creepy Cruiser]

Hey Matt, when you figure it out let me know, mine's been doing the same thing for over 15 years, lol.

 

When it starts getting bad, I just replace the cap and rotor with a new Bosch set and it goes away for quite a while. Also if I run anything in it other than Premium, it gets really bad. Not sure why it effects it, (because it shouldn't), but it makes a huge difference. Look in your cap and see if one of the coil legs is melted off, that's when you know it's really gone bad, lol.

[HRH]

I talked to nismo dr on this some and one of the things he mentioned was the CAS (distributor) ground lead will show good, but is not. The solution is running a redundant ground from that connector, which I also did. Did seem to help a little bit, but the overall problem is still there.

 

I read a long time ago on some issue regarding the harness on the hardbodies having a break in it, right where it split off, but for the life of me I can't remember where. Going to have to find that article again if it's still on the web.

 

 

Had a new cap and rotor wires plugs all that in the last 1000 miles, so shouldn't be it. Plus it doesn't do it all the time, though it seems to get worse the hotter it gets. But then it's also bad right between the transition from closed loop to open loop.

[HRH]

So going around the interwebs, I ran across this. Forgot I had a similar issue on a previous hardbody, though it was much less. Perhaps less because it was 2wd and I wasn't lugging around 1000 extra pounds which tends to amplify things. I never did figure that one out, just ignored it.

 

http://www.autosportsnorthwest.org/forums/viewtopic.php?p=1720&sid=4852c10d785e697f60cc2808e3eeccb9

 

I am considering replacing the IAC valve. Cleaned it on the NX to no avail, figure since I can get them cheap enough, I may try that with the hardbody.

[HRH]

Where'd my post go? Okay, that's weird, I totally posted something and it didn't show up. Anyway, found something interesting regarding the fuel pump being controlled by the ECM.

 

When the CAS unit in the distributor senses the 1 degree slit signal, it says okay, the engine is turning, and sends signal to the fuel pump. If no signal, the ECM shuts off the fuel pump to save battery because obviously something is wrong and the motor won't run.

 

So this could explain the hot-start problem I'm having where I get it warmed up and run it, then shut off and leave for a half hour or hour. Coming back and trying to start it still cranks, but takes a long time to get fuel pressure. It was as long as four seconds while reading 0 pressure during yesterday's procedure, before it finally got fuel pressure and started.

 

Now, let's just say the CAS is failing or dirty. That COULD lead to the intermittent hesitation off idle as it doesn't sense the slits and momentarily shuts off pressure. The annoying thing about this is it's integrated into the distributor and to buy the CAS unit itself is nasty expensive. Better off to buy the whole reman distributor, but then I'll have to swap guts since my dist has been lathed down to fit in the Z24 housing instead of the KA.

 

The only test procedure I see is turning by hand and voltage should oscillate between 5v and 0v. If I can do the hot test again and get it to malfunction, that would be great. Somehow though I imagine it's going to show me it's good. We shall see.

 

Now that I think about this, I keep remembering that old mechanic's creed: "90% of fuel problems are found in the distributor." :)

[Creepy Cruiser]

Interesting, maybe I should try swapping in an extra dizzy that I have and see if it fixes my issue then.

[yello620]

Had a new cap and rotor wires plugs all that in the last 1000 miles, so shouldn't be it.

 

 

Would be nice to think that, but i bet you installed Belden wires didn't you.

 

I have had to warranty way to many sets of those damn things.

[HRH]

Oh ho, you think so? :P No, I have a nice set of NGK wires on there. Great quality, very pleased with them. Belden does seem to have lessened their quality in recent years, but still not too bad.

[HRH]

AH HAH! So Ken at Kentech (local shop, was a Nissan master tech for 20 years, good guy) told me I should check TSBs. And I went online to Nissan's site which they list the TSBs, but want you to subscribe to get ALL the info, though on some they tell you basically what's going on. So I didn't want to pay $20 for a one-day subscription, nor $720 for a 1 year subscription, so I went up to Sears where Buddy works and borrowed their computer. Our Mitchell's at work was basically useless, only listing 5 TSBs total. Sears has all-data which is much better.

 

Problem one of hard starting due to loss of fuel pressure after key-off: NTB 94031. They make it sound all mysterious, and I open it up and it's two lines. "Replace original pump with countermeasure pump and replace o-ring." Really? All that for "replace the part." Anyway, most definitely that is one problem so a new pump will be installed. I hope that takes care of the other problem, but it may not.

 

Another issue not so much on my list is NTB 94106, which is idle fluctuation. I don't really have that but I may check this anyway. Where the B/G ground from the ECM meets 3 other wires for the coolant temp, EGR, and TPS can have a connection that is crimped but faulty, in which case the ground will be intermittent which will throw bad info to the ECM. I think this is right around the throttle body, but they don't show a picture in the TSB. I've seen a picture before, but can't find that website anymore. Either way, shouldn't be that hard to find. Cure for that is to unwrap and solder the connection and no more issues.

[yello620]

Oh ho, you think so? :P No, I have a nice set of NGK wires on there. Great quality, very pleased with them. Belden does seem to have lessened their quality in recent years, but still not too bad.

 

Agreed, the NGK's are good. :D

[Creepy Cruiser]

Very cool, keep me posted.

[ggzilla]

TSBs are free to look up. But not at every web site, some want you to pay.

 

But don't forgot the common causes. For example, bad spark plug wires can cause hesitation & light bucking. You can test them with an ohmmeter:

* Visually inspect the spark plug wires carefully for cracks or burn marks. Throw away any that have them.

* Measure resistance with an ohmmeter. Resistor wires (modern wires) should be around 10,000 ohms per foot. Throw out any with resistance too high.

* Check the metals ends of the wires and the distributor cap. If one end is oxidized compared to the others (e.g one plug end is oxidized, the other three are shiny), that cylinder isn't firing correctly. Could be the cap, the wire, a vacuum leak, bad cylinder compression or some other reason.

[HRH]

This is true ggzilla, but in my case everything on/in this motor is brand spanking new. Anyway, here we go with pictures of the starting of the fuel pump switcheroo.

 

The biggest fear I have after reading some other people's D21 build threads on other forums is snapping the bolts that hold the plate on the fuel tank. 6 bolts. Hit them with PB Blaster tonight, then sprayed all the dirt/mud off with the hose, then came back with WD40 to displace the water, and in the morning I'll hit them with PB Blaster again and cross my fingers.

 

Broke off one bed bolt which should be easy enough to replicate. They sit in the frame channel of the bed with little wings, should be able to put a rectangular washer on a regular bolt and accomplish the same goal. We shall see.

 

I'll be uploading pictures in a minute, apparently godaddy had some security issues and as a result they reset my password for the server. In the process of changing that now, hopefully will be done soon.

 

Oh yeah, the stuff used to lift the bed is mule tape. Got it from a friend a long time ago who worked for the phone company. They use it to pull line through conduit. Little 1/2 wide strap, 1800 lb test. Bitching material.

 

 

 

 

 

 

 

 

 

 

 

 

[wildmaninid]

Looking good. Afraid to drop the tank? That shits easy son!

[motavated]

Might as well clean and paint the frame. LOL!

[HRH]

Hehe, yeah, easy, especially with no lift! I hate dropping tanks. Plus you have to disconnect a shitload while underneath. 10 bolts total for the bed off. 6 main bolts, 1 ground strap, three screws in filler neck. Viola! Took me about an hour start to finish, only because I had to jockey the cars around, push the other motorless 510 out of the way, get everything aligned, back the truck in, check on the people outside puking on the curb (too much beer) and then finally lift the bed off.

 

I like room when I'm working on my shit. Coolest thing I ever saw was a Jeep with fenders hinged at the rear, and they swung open to be able to easily work on the engine. I would LOVE to do that to the hardbody.

[HRH]

Dammitall, have I mentioned what a pain in the ass it is trying to get the bed aligned juuuuust right? I neglected to measure the distance between the cab and bed. I remember it as being hard to get my fingers in, so 7/8 inch or so. Anyone have a hardbody they care to go measure the gap right above the body line?

[ggzilla]

So what would make the fuel pressure drop?

The regulator could have gone bad. I doubt if it is the pump as you reach the full 43psi while it is running.

[HRH]

ggzilla, you must not have read the whole thing! ;) See post #9. Regulator has been tested to death, it is fine. One interesting thing after bringing home the wrong fuel pump is the correct '92 fuel pump (it's a late '92) has a pressure valve dingus built into the pump. Can't remember if that's just to prevent the line from "water hammering" or if it's a separate pressure regulator in addition to the one at the rail.

 

Anyway, bed is finally on, actually looks better than factory for the distance between the cab which seems to be about 7/8". Going to eat lunch and take the dog for a bike ride and see how she works. Hoping this may have had some effect on the light throttle fluctuation issue, but that remains to be seen. I wouldn't be surprised if that issue is still there. Either way, one problem is fixed.

 

I'll post pictures later.

[ggzilla]

I didn't see that you tested the regulator pressure valve. The part that keeps the pressure up after you turn off the pump. On earlier Nissans there was the regulator in the Injector loop, and a regulator/damper back near the fuel pump. Maybe it doesn't apply to the in-tank kind of system.

[HRH]

Alrighty then, I think these pictures should clear up any confusion. The truck is back together and running well. Not any hard start issues today. Get in, about 3 revolutions and it catches, just like it should. The 2000 rpm hiccup is still there. The solution is to not run it at that rpm unless in 1st or 2nd, as I think it's partly a lugging issue. I have a theory that because it's such light load and it's right at tip-in, the system is going back and forth between idle circuit and normal running and given the low rpm, starts to stutter back and forth. It also might be exploiting the slop in the drivetrain, which doesn't help. Either way, I don't think anything is wrong with the truck. ECU says all good, all sensors have been checked and everything is new. So, decided I'll drive it like the 510. I don't drop below 2500 generally unless coming to a stop. That has a lot to do with gearing but also the cam overlap.

 

So without further ado, here are the finished pictures of the fuel pump swap to address the Nissan TSB.

 

 

 

 

 

 

 

 

 

[HRH]

 

 

 

 

 

 

 

 

[ggzilla]

So what exactly did you do to the pump? Just replace it?

[HRH]

Yep. Per the TSB, pump was defective, randomly drops line pressure for no good reason.

[HRH]

AH-HAH!

 

Finally found the issue I've been chasing for months! So the hesitation under light load, say 4th gear, 2000 rpm, flat ground, around 40 mph right? Ever so slight, tach stayed dead steady but you could feel a back and forth motion in the drivetrain.

 

Went to CDA the other day and like always the freeway driving was fine. It's been getting colder here lately. Into the 40s/50s by day, 30s at night. I get off the freeway and start down 41 toward Rathdrum prairie to cut over to Hayden where my buddy Mike lives. Anyway, the truck starts shaking like a paint shaker. Not bad enough to stop driving, but definitely got me thinking more about the tires. So I check them over and find that the small heat checks have gotten a bit bigger and now circle about a 1.5" foot section of tread. Rest of the tire is fine.

 

So I called my buddy Justin at Sears, told him to order me in two BFG TA KOs and went in this morning to get them changed out. Examining the old tires, there were rubber bits on the inside and it was apparent that the tires had started de-laminating. These tires were brand new almost no miles BFG TAs, but old, not KOs (newer style). Talked to Justin, the guy I got them from was an acquaintance and turns out he must have had these on his Jeep before he switched to bigger tires, and probably had it outside in the sun sitting for a while before he took them off, unused, and then stored them in his garage for quite a while.

 

They lasted a little while, and weren't so bad this summer and the heat checks (cracks) weren't there when I bought them, so looks like they just fell apart due to storage and non-use conditions.

 

Anyway, put the new tires on this morning, been driving all day, haven't been able to make it do the hesitation/stumble/surge/nasty thing it did. So I'm all freakin' happy now! :D