Loses power under load

[p3dave]

I finally bought the Z car I always wanted (well I can't afford a 240) a 1979 280ZX (which was the year I went in the Navy and while other guys had Z cars I had a 1974 Ford Country Sedan Wagon . Just drove it home and after running fine for about 20 minutes when I got on the freeway it started to "jerk" by losing power going up a slight incline and then surge back gradually going from 65 to 40 mph. I tried to nurse it home but it got worse until it was doing it on the level road and I finally pulled over and got a tow. Called the guy I bought it from and he suggested the fuel filter which looks new (he took the car on trade) but I'm going to go get one and replace it. A couple of injectors were replaced recently. Has anyone else had something like this or have ideas?

Excited to be a part of the group!

[d240zx2]

A plugged filter certainly could be the source of your problem, but be prepared for others...

[Zed Head]

I would check fuel pressure first. With a fuel pressure gauge, you can check your pressure before and after the filter change and know if you did anything. The gauges are a little spendy and you think you won't use it much but the they're a good tool for problem-solving. If it ran for 20 minutes then conked out, a faulty fuel pump might be more likely, or a clogged fuel inlet. If the filter is clogged it will still be clogged when you test pressure. Either way, with a gauge you can confirm pressure before taking it out on the road.

[240260280z]

All of the above

Drain tank and see what comes out (there is a drain bolt usually on the bottom).

Ensure pump and Fuel Pressure Regulator are working fine.

Also check the ignition system. The ignition modules usually fail from heat. When they are dying, once cooled down (after the car sits for a while, they work fine untilhot again)

[zbane]

Drain tank and see what comes out (there is a drain bolt usually on the bottom).

Actually, the S130 fuel tanks do not have a drain plug but loosening/removing the fuel filler hose (at the tank, obviously) will do the trick, though this method doesn't completely remove all the gas. Still, it's pretty easy to remove the tank itself, even with some gas in there.

I would suggest throwing some money at the car through a few new parts. They may not be needed, but since you don't know the last time these were installed, it wouldn't hurt.

New NGK spark plugs, fuel filter, fuel pressure regulator (on fuel rail), air filter, and distributor cap/rotor.

[black gold man]

Do you have any red lights on dash. If you charged the battery to get it going or had to jump start it. Low battery and bad alternator will make the car run like that.

until it dies.

[p3dave]

Thanks for all the responses so far, great to have the group as a resource! When I pulled the filter off gas spurted out and it was full. After draining it I blew through the "in" side and could blow through but the new filter has less restriction to air. I also have picked up some new plugs and wires but have to order a cap/rotor. I inspected the current cap/rotor and will sand the contacts but they aren't too bad, no scoring on the sides or cracks I can see but I will replace anyway. Also ordered the fuel regulator and a friend is going to bring a pressure gauge to test the pump. The car had been sitting for an unknown amount of time but the guy I had bought it from had driven it 50-60 miles. I didn't start having problems until I filled the tank (with midgrade) and it took about 12 gals so I guess the tank holds 21+. About 5-10 miles after that when I entered the freeway it started to cut out and then resume on slight inclines and by the time I pulled off, it was doing it on the level road with more cutting out then resuming. No red lights except a "door ajar" which I assume is a bad switch, that batt/alt appear to be functioning and no jumps required. I did notice in the "fusible link" compartment that the "EGI" ??? link had apparently blown and someone had twisted the wire together without solder etc., so I'll be replacing that but not sure what EGI is yet. I'll post my progress.

[p3dave]

I changed out the fuel filter and while I was doing that I was checking the wiring in the engine compartment (not in depth just taking a look for anything obvious) and it is clear that this car has had some barnyard mechanical work done (no offense to any barnyard mechanics out there). Looking under the distributor I spy a small black c clamp about 3 inches long. The tension screw to allow for timing adjustment had broken off and rather then drill it out or whatever, someone clamped it in place. That is surely a long term fix :-) Anyway, after messing around a bit I turned the key to on and heard the fuel pump (not hard it is a noisy bugger and will be replaced). After getting fuel back into the system she started up OK and I was able to drive around the block with no issue. I'm going out for a longer jaunt here but not far from home. If there is more contamination in the tank, this filter will clog up to if that was in fact the issue.

Another thing I noticed was that at idle the oil pressure indicates middle of the gauge but when I start driving or reving up it drops to zero. Thanks to David I have a copy of the service manual and last night while checking out the EFI system I noted that there is a link between oil pressure and fuel being provided. There is also a link with the alternator (this is the way I am interpreting it anyway, please correct me) for this same reason. However, it appears either one or the other will surfice to keep fuel flowing. I guess this system is some type of safety cutoff in case the engine stops? Does the oil pressure indication sound like a gauge or sensor issue?

[p3dave]

OK, drive was not too long as it started to cut out again at speeds at or under 40 mph. At his point the car was warmed up and water temp was mid gauge. When oil pressure was indicated it was mid gauge and charging was 14V, all normal I would say. Once I got back home I ran it in neutral and it would go up to about 4,000 rpm and cut out dropping to 2-3,000 and then running up to about 4,000 and cutting out. After a minute or two of this it dropped to almost zero and I took my foot off of the pedal and it recovered. Idles normally. Hopefully my friend will bring his pressure gauge over soon.

Any new ideas based on the above?

[p3dave]

Now I am getting frustrated. So far I have (not in this order) replaced cap, rotor, plugs, wires, fuel pump and no difference. Checked the fuel pressure before the pump and it was indicating 30 at idle, dropping when accelerating and when the "cut out" occurs, dropping even more...so changed the pump. No difference. Started to suspect the "damper" mounted near the pump, ran the hose direct by-passing it and no difference. Have not changed the pressure regulator although I bought one since all this appears to be happening before the rail unless I'm missing something. Suspected the old pump since it was making a racket but the new pump is even louder (it is an Airtex bought at an auto parts store. On the test drive I noticed that when the power cutoff the fuel pump got quiet also? Not sure if this is the "failsafe" that cuts off fuel when power stops or something else.

Help!!!

[p3dave]

Well, we siphoned some gas out of the tank from the fuel pump inlet hose. The flow of fuel was much lower then expected. Once we got some gas in a bucket we ran a hose from the fuel pump inlet to the bucket and ran the pump. No noise from the pump as it ran. Then started it up and the pressure gauge indicated normal pressure at idle and with acceleration. So, tomorrow we drain the tank and drop it.

Also some particles of grud/corrosion were in the bottom of the bucket.

Thanks for your suggestions and keep your fingers crossed!

Dave

[Wade Nelson]

I didn't bother to read the entire thread, but a failed Throttle Position Sensor will cause you to lose power under load, runs fine most of the time otherwise. Not too hard to do a quick check on with a VOM.