Hey all, I recently was given a beautifully running 280ZX 2+2 GL by a friend. It needed a new clutch slave cylinder, and after that it ran great until these past few days. Basically, it'll run fine when I first start it but once it starts to warm up, it bogs down at increasingly low rpm's. Like after a warm-up at idle and a 5 minute drive, it won't go past 4,500rpm...Then as you keep driving it starts sputtering and surging at even lower RPM's until it's barely driveable.

What I mean by sputtering and surging is that it acts like it just won't burn the fuel it's being given - Once I let off the throttle it'll backfire and increase RPM's a little but if I try to add any more gas to keep going it'll do the same thing, and it'll do it over and over.

I replaced my cap/rotor/plugs/wires yesterday to try and fix the problem but it didn't work. I also took the AFM apart and gave it the polish of a lifetime and adjusted it. The coil looks pretty old so that may be my next purchase. Tomorrow I'm going to check the TPS for corrosion and adjustment. I'm also running 93 octane in it so maybe I'm over-octaning it? I don't know.

I'll give you guys a brief history on the car, it sat for several years before I got it because it wouldn't pass inspection. It's very beefy - Full exhaust, injectors from a turbo, a cam (not sure which), the top end was balanced/adjusted by a local Z specialty shop, upgraded swaybars and struts/springs. It's got some rust but it's a 280ZX...

Any ideas, suggestions, theories will be appreciated.

 

Hehe, chick question, but does it have gas? Mine does the same thing when it's running out......that's just my two cents. What about fuel filter?

 

It's got just under a 1/4 tank, which I'd assume would be enough. Fuel filter should be good, I unhooked the top hose and it shot fuel all over the place somethin' awful.

 

Well, I'm currently outta ideas. (looks for the men here to help) ......and welcome to ZDRIVER ^.^

 

Ouch ... next time, disconnect the fuel pump (connector is located the center of the rear cargo area, under the carpet) then try to start the car. That will release the pressure and cause less spillage when removing the fuel filter hose.

 

lol, ok, another gal

 

Usual problems with your symptoms:

AFM
Distributor - Check your timing
Vacuum Leak - While engine is warm and idling, unscrew oil cap and see if there's any change in idle
EGR - disconnect the line while engine warm and idling, and see if there's any change in idle
Fuel Filter - If you haven't replaced it, you should
Fuel Injectors
02 Sensor

 

if all those check out and you suspect a vacuum leak, spray starter fluid around your intake vacuum hoses and listen for your idle to change suddenly.

 

Well, unless you have something controling those turbo injectors its probibly running beyond all richness, which explains the smooth idle, but as soon as you get on it theres not enough air to compensate for all that fuel. You have to remember that the ECU is tuned for the injectors it has. Try finding a non turbo at the junkyard and get the injectors.


I'm no expert but I'm sure someone here can back me up.

 

Yeah but, the car's not exactly stock and as I mentioned previously, it ran beautifully up until two nights ago. Then the problem started, since then it's been getting worse and worse.

 

A F M = No Bueno

P.S.
Welcome to ZDriver!

Rod.

 

ill give my 2 cents, has the engine recently got wet? cause if so, the crappy connectors in these 25 year old cars corrode and short with moisture, also those injectors if controlled by the stock computer are too much, you would need a step inbetween stock and turbo, or a aftermarket fuel program, trust me i know, my n/a is on stock ecu/injectors running really strong, and im just strating to run outta fuel at the top end only. check the tps sensor, on the throttle body, it can cause simmilar symptoms, as well as the head temp sensor.

 

Yeay, The Guys Show Up!!! ^.^

 

Yeah the engine actually has gotten wet recently, I had the hose that goes out of the head for the heater bust on me and it shot water all over the place. I fixed it but the connection itself started leaking on me as well without my knowledge. So now that's fixed too. Water was all over the starter motor and those connections from the battery but I figured they'd be ok once they dried out.

Not sure what electronics are in the car, all I know is that the guy who gave it to me said they were upgraded, and another Z enthusiast told me they were the injectors from the turbo model.

 

It's easier to just take out the fuel pump relay in the engine bay right next to the fuel filter. It will be the largest out of the four.

Let the car idle
pull off relay
wait until car dies
no more fuel, no more pressure

 

I've tried that, and found that disconnecting the harness to the fuel pump itself reduces the most pressure.

 

Definitely check your ignition timing. The fact that it started out of nowhere being that goofy either sounds like major vacuum leak, ignition timing, or AFM.
On my car the ignition timing was right, but when I replaced the Ignition Module/Ignition Coil the timing was thrown way off. I think my coil or module was bad and giving me just the wrong spark setting so that when they were correct my timing was way different.

 

I'll try that but here's a newb question, how do I use a timing light? A friend let me borrow one and I've got no clue how to use it, I've always tuned timing by ear.

Also, how far do you think I could safely advance the timing running 93 octane? I'd like to know for when the problem gets fixed.

 

Ok, took it for a short trip to the store to get it warmed up to check everything else and now it's doing it even when cold. But if I blip the throttle repeatedly or hold it steadily about 1/3 the way down it'll rev beautifully, but adding any more than that (or driving in gear) and it'll act like it's got no ***** at all.

I did the engine oil filler check for vac leaks and it checked out good, I think I'll try to adjust the AFM again and clean the TPS. I need to find someone with a multimeter too...

 

I'm still not really clear on exactly what the symptom is... At first it sounded like an AFM issue, but from the way you have occasionally described it... It could be the good ol' "I got my TPS connector Wet" syndrome too...


Could you be more specific about exactly what it's doing?


Rod.

 

Well...When driving it'll start stumbling and dropping RPM's if you try to give it gas. When revving in neutral or with the clutch pushed in, it'll rev but you can't give it more than just the littlest bit of gas or it'll do the same thing it does when driving.

It's like the ignition is cutting out when I give it gas because once it cuts back in, it'll backfire and gain a few RPM's.

 

sounds like the tps sensor is wet, unplug, blow dry, or use wd40 (stands for water displacement) then re-plug and drive, try that for me dspec. the timing light connects to your batt. and the other lead connects to your #1 spark plug lead. then at idle, point the gun at the timing mark on the pass. side of the engine bay, you may need to get the serivce manual to find it more easily and read the marks, easch tick, is 5 deg of timing, for now, to solve your problem, stay at 10 deg timing. then once the problem is figured out, move it to 15 deg. try not to exceed that, cause you wont have any bottom end, or top end, thats why the manufacture states that the timing should be 8 deg, but thats just an all round good #. we can fudge that a bit.

 

Update: Readjusted the AFM, problem is still there. Although when I pulled the battery wire to reset the ECU it seemed to go away for a few seconds, but that could be my imagination running wild.

Edit: Ok, do you mean the harness or the TPS itself?

 

Sounds to me like it's either loading up, or leaning out... My money is on loading up. This takes us back to the earlier discussion about having over-sized injectors. The only caveat is of course the fact that you say it just started doing it and it was running fine before. Could possibly be Fuel Pressure Regulator problem, but that is doubtful.

Try backing the AFM adjustment down as described in the "How to rebuild your AFM" Sticky thread under the performance/technical 280ZX section. If you can lean it out enough to run better, you will know that it is definatly an over-fueling problem. Then you will just need to determine why it is dumping too much fuel. You don't want to just adjust the AFM and keep running that way, or you risk being too lean at higher RPM's and doing some serious engine damage.

But, that will atleast help to determine the true nature of the problem.


Rod.

 

I'm buying my brother's A/F meter out of his car and am going to install it today so I'll be able to tell later on if it's running rich or lean. I've tried adjusting the AFM both ways and honestly, adjusting it leaner made the problem come on sooner, and adjusting it richer made it come on later. Now it doesn't matter as it'll barely drive at all.