What next?!

[ktm]

K.I.S.S.

Your best bet is to test "Various electrical measurements on the EFI, per the FSM.

Otherwise, everyone is guessing in the dark and making you a car hypochondriac.

You know you are running rich, therefore that can help you reduce the scope of your diagnosis. Unfortunately I do not know too much about the stock ECM as I am running a modern aftermarket EMS. However, the FSM does have a detailed procedure for testing each circuit/function and the respective specs.

[FastWoman]

Point taken about the solder joints.

Bart, the oil filler cap does introduce air after the AFM -- via the hose between the valve cover and the inlet to the throttle body.

ktm, you're right, of course.

Update: I haven't quite finished removing all of the old fuel rail. I still have 3 frozen injector screws, and one mounting bolt snapped after I had turned it several turns. Still soaking with WD-40, and I'll be drilling out the bolt tomorrow. If the screws still won't turn, then I may end up drilling off the heads, removing the injectors, introducing WD-40 closer to the corrosion, and backing them out with double nuts.

It shouldn't be this hard to remove these screws and bolts. I don't think a bit of antisieze compound was used on any of this hardware when the previous owner had a single (yes, one) injector replaced 5 or 6 years ago! I've done injectors before. I've never had this much trouble -- not even close!

I'll also check out the cold start valve tomorrow before reassembling. I have a spare valve, so I can clean both and use the better of the two. (I'm optimistic that at least one will be good.) I also have a new filter, so my fuel system will finally be reworked from tank to injector -- clean tank, new hoses, pre-filter, flushed pump, new check valve, cleaned damper, new filter, clean fuel rail, new injectors (with fresh wiring and connectors), cleaned/checked cold start, and cleaned/checked fuel pressure regulator. I went through a lot of crusty/crumbly equipment to get to this point.

More tomorrow!

[Z train]

My point about the ECM is that it is the beginning of the system.On a vehicle this old(or just basic trouble-shooting)you need to establish a good baseline.So if appropriate verify the ECM and move on.My ECM drove me nuckin futs before i found the issue.

[mlc240z]

Skip the WD-40.

It's useless on rusted fasteners. At least useless by comparison.

Buy some PBlaster or Kroil.

I've used PBlaster since I read about it on this forum and it is SO much better than LiquidWrench (which used to be my standby).

[FastWoman]

Kinda late... But I'll try PB Blaster the next time.

Update: I spent the entire afternoon on the rusted fasteners. I extracted the bolt and cleaned up the threads just fine. Then the three injector screws. (These seem to have been rusted in place by a very slow coolant leak the previous owner had let go -- the one to the air bypass.) I've never seen anything rusted in place so badly. I finally drilled the heads, pulled the injectors, and then worked on the long stubs to extract them. The only thing was that the last screw -- the lower #1 injector screw -- would NOT come out. I could turn it back and forth, and I worked it back and forth for maybe an hour, working WD-40 down the hole all the while. I made about 5 turns progress before the screw died of metal fatique and gave way at the base at an odd and rather difficult to drill angle (considering that the throttle linkage tower is in my way). Grrrrrr....

So now I'm trying to figure out what to do.

I need to replace the exhaust manifold gasket anyway, so maybe I pull both manifolds and run the intake to a machine shop for them to work their magic?

[LeonV]

Skip the WD-40.

It's useless on rusted fasteners. At least useless by comparison.

Buy some PBlaster or Kroil.

I've used PBlaster since I read about it on this forum and it is SO much better than LiquidWrench (which used to be my standby).

That's funny, I had the opposite experience! I used PB for a while until I read that Liquid Wrench is better in an article. They backed it up with some testing as well.

I finally got my spindle pins out after using Liquid Wrench. I'd been going at it with PB for a looooong time! I don't know whether it was coincidence or not, but Liquid Wrench has been working very well for me. I switched to LW because it's what my local store had. Looks like ATF/acetone home-brew is the best bet, out of the tested choices.

[Nazgul280]

Bummer about those injector bolts!! Use anti-seize on the new ones and you won't have that problem again!

I've read your posts, and it looks like you've put a lot of thought into this. I just have a few thoughts that maybe you can consider...

1) Good idea to replace the temp sensor that you know is bad, and sticky injectors will certainly enrich the mixture.

2) Air leaks will make it run lean, and possibly raise the idle speed.

3) Cold start valve continually operating will keep it rich, and it's tied into the temp sensor for the cold start cycle. If in fact your ECU always thinks the engine is too cold it will run on the enrich schedule with the cold start valve.

4) One thing you or anybody else did not mention: if after all those above still haven't fixed it, then I would pry open the black dust cover on the AFM and reference the Z Tech Tips related to the AFM.

Here is a great place to start for the theory and help about a rich running Z: http://www.atlanticz.ca/zclub/techtips/runningrich/index.html

5) As a last resort, adjust the AFM teeth to change the overall fuel mixture. This will change the mixture on the entire bandwidth. Also, you will probably see if a previous owner has messed with it. I don't know if you developed this problem recently, or if it was always like this, but sometime you inherit problems created by POs. Often times people will mess with the AFM setting to cover a problem they can't find, then, when the other problem is corrected all of a sudden the car is not running well. Here is the link for the detail and adjustment (which is HIGHLY informative): http://www.atlanticz.ca/zclub/techtips/afm/index.html

I encourage you to reference these directions and I feel certain you will find your problem...keep going and you will have success!

Don't forget to post the results when you find the solution so we can all learn and for the benefit of those who come after you.

Good luck!:classic:

-Dana

[FastWoman]

Thanks for the encouragement, Dana. I keep looking back on that last screw and thinking, gee, maybe I should have soaked it for a week, or maybe I should have used two nuts and a socket, instead of a small vice grip. I keep kicking myself over it, but I know I gave it my (almost) best effort. The thing about it, though, was that the first couple of turns were only moderately difficult -- with a screwdriver, even. As I said, though, the manifolds have to come off anyway. I've had the manifold bolts soaking in PBlaster (thanks for the suggestion, Bart). I'll probably give them a try today.

I've already studied the AFM adjustment info on the Atlantic Z website. That's a great resource they've got. Right now I'm looking at my system much the same way you probably are -- a mixture of malfunctions, some of which lean the mixture, some of which enrichen the mixture -- all of which work in combination together and in opposition to give me a (poorly) running and somewhat unresponsive engine.

I did pull the cold start valve yesterday, and it appears to be stuck open. I also noticed some damage to the lower EGR gasket, which I hadn't replaced when I replaced my EGR valve. (The big iron spacer was stuck in place, so I didn't think it was necessary.) There may be a leak in the intake manifold gasket for all I know. I found another small leak where a fitting was loose. I'm sure I'll discover lots of interesting stuff.

My general approach will be to go through the entire system, component by component, to ensure that it is mechanically and electrically sound. Then I'll see how it runs and make my final adjustments to the AFM.

That said, I'm considering a minor redesign of my fuel rail (see thread in the EFI section). I'm considering incorporating an adjustable fuel pressure regulator in that design. That can be used to fine-tune fuel/air ratio a bit more easily than cracking open the AFM. What do you think?

I've found these nice looking regulators on Ebay, but they seem maybe "too" inexpensive. I presume they're made in China:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=170535789792&viewitem=&sspagename=STRK%3AMESINDXX%3AIT

Also with such a broad adjustment range of 0 - 140 psi, I wonder how accurately I'd be able to adjust the fuel pressure.

[Z train]

Fastchick-i think you're getting way ahead of yourself.Fix the stock system in the stock configuration.There is nothing wrong with it all things being equal.Then move on from there.

First thing i would do is install an inline fuel pressure guage between the filter & the fuel rail.The readings will tell you volumes.

[FastWoman]

Ztrain, I have a gauge I often have temporarily installed inline. I don't think it would last very long as a permanent installation, but I don't mind driving around with it for a day or two or three.

Just altering the plumbing isn't much of a mod, functionally. If I can set the stock pressure, nothing has really changed. Right?

[Nazgul280]

I'm considering incorporating an adjustable fuel pressure regulator in that design. That can be used to fine-tune fuel/air ratio a bit more easily than cracking open the AFM. What do you think?

I've found these nice looking regulators on Ebay, but they seem maybe "too" inexpensive. I presume they're made in China:

Hmmm, they look like Aeromotive knockoffs to me! $130 vs. $28. Either that's a good deal or we are just paying too much for name-brand regulators!! Looks like they have a 7 day return policy, so if you hope to get a refund on a defect, don't buy it until you are ready to install and run the engine again. It looks like what you need if that's the route your going, which is a slippery slope in the world of modification. :classic:, but the price seems too low: the gauge alone is usually 10 bucks, and they are supplying the fittings, hose, and mounts too. I'd have a backup waiting if it doesn't work!

I'm thinking you're only going to need an adjustable range of 30-45 psi. If you are going to get a fuel rail (I responded to your thread in the EFI forum), you might as well get a permanent fitting and fuel pressure gauge, which can be found easily on Summitracing.com or other popular aftermarket performance suppliers like Jeggs, etc., and stick it near the fuel rail. I did it, and can see the difference in pressure between my FPR and upstream at the beginning of the fuel rail. That way, I can adjust the pressure accordingly.

Sounds like you are on the right track. These L28s are notorious for leaking at the exhaust manifold at the #6.

[Z train]

Ztrain, I have a gauge I often have temporarily installed inline. I don't think it would last very long as a permanent installation, but I don't mind driving around with it for a day or two or three.

1)Just altering the plumbing isn't much of a mod, functionally. 2)If I can set the stock pressure, nothing has really changed. Right?

1)True

2)I want to agree,but something is sticking in the back of my mind and i can't put my finger on it.Maybe something to do with vacuum.

ANd i tend to agree with Nazgul about the reg.Too good to be true.Hit up your local speed shop.