Severe Power Loss = HELP!!!!!!!!!!!!

[AZ260Z]

The Problem: What started out as an intermittent power loss during acceleration has progressed to nearly a constant problem including at start up. I am now relegated to starting the car in the driveway and an occasional trip around the neighborhood. It does however has it’s moments. Just 2 months ago after not starting it for a couple of weeks, it started up, idled smooth and revved up smoothly so I took it out and it didn’t act up so I took it on the closest highway and had it up to 80mph and had a lot more but was afraid of getting a ticket. The total trip was only about 30 minutes, I was elated. Decided to try it the next day and it acted up on start up. This has been going on for the past 5 years and am on the 5th mechanic not counting the countless hours myself and friend have spent trying to diagnose the problem.

Background: I am the original owner of the 1974 260Z w/manual trans. I drove the car for 14 years, parked it for the next 14 years(Bad Idea!!), then decided to get it running again in 2003. After a lot of time, $$$, a friend, my old “Z” mechanic(who has since retired & moved out of state) we got it running. It ran great but after a few hundred miles I noticed condensation coming out the tailpipe. I took it into the shop and discovered the water jackets in the head had rusted out and couldn’t be repaired so had to put a rebuilt head on. Drove it occasionally around town for the next few years for another 1300 miles. The only problem it had before and after head replacement was it would get hot if sitting at idle for any length of time. Decided in spring of 2005 to give the car more of a driving test by taking a day trip from Phoenix to Flagstaff. About 30 miles into the trip it started overheating so I pulled off the highway (steam was coming out the overflow tube) let it cool down, then added water and took it easy, monitoring the temp gage all the way home. Shortly thereafter I had the radiator rodded out and replaced the fan clutch which seemed to cure the overheating problems. The car seemed to be fine, so I put that incident behind me. It could have been months or even up to 2 years before this current problem arose. It’s hard to pinpoint the timeframe(sometime in 2006/2007) because of the infrequent use of the car but I know it was long enough not to associate the overheating with this current problem. In 2008, thinking it was a fuel issue I replaced my original flatop carbs with older roundtop rebuilt SU’s with the hope it would solve the problem. It had zero effect.

In 2009 I took the car to Mechanic#1, he too thought it was a fuel issue. He drained some fuel from tank, poked around inside the tank looking for obstructions, replaced electric fuel pump & filter, all with no improvement. He swapped out the coil and ballast resistor with no improvement so reinstalled mine. He then replaced distributor cap, rotor, plug wires & plugs, no improvement. He had the car for 4 months and finally gave up (under duress from his boss to either fix it or move it).

During this time I was reading literally hundreds of posts on this site looking for similar symptoms and solutions. Unfortunately these symptoms can run the gamut from fuel, electrical, spark, timing, etc.

After getting the car back, I replaced the alternator, voltage regulator, and swapped out a pick up coil, spare distributor, spare transistor ignition unit, all with no impact on fixing the problem. I also pulled all the electrical connectors apart and used deoxit on them, nothing.

In 2011 I took it to mechanic #2 which in addition to general work, they specialized in electrical problems. They called me and said they suspected it was a fuel issue but couldn’t be specific. They even took the car to their other shop who had an older mechanic. He checked it out and said it could only be 1 of 2 things, either back pressure or the timing chain had jumped a tooth. They called back a few days later and said it was nether of those things and they still think it might be a fuel issue and recommended a carburetor specialist. So to put this to bed I took the car to him (Mechanic#3). Turns out, he’s an older guy, runs a 1 man shop and does nothing but work on carburetors. He even owned 2 different “Z’s” in the past, so he was very familiar with SU’s. He went completely through the fuel delivery system, checked pressure, volume, plugged lines, etc. He fine tuned the carbs and said it was running great. He then went to back the car out of the bay and it went into the no power mode. He called me and said I don’t have a fuel issue. I still had a gut feeling it was an electrical issue so after researching and talking to mechanics. I was referred to a guy that did nothing but electrical and had a mobile service and did consulting work for several repair shops in the area. I contacted him(Mechanic#4) and he gave me his rates and said it would be cheaper if I could bring the car to him. So I raced over to his place(max speed of 25-30mph) He called me that afternoon and said I didn’t have an electrical problem and was getting spark to all cylinders. He did notice that there was no discernable difference when pulling the plugs out individually on the front 3 cylinders. He then suggested I take it to Mechanic#5 who he said was honest, reasonable and knowledgeable. He called ahead and told him I was on my way. After having to climb some inclines and venture into a rotary at rush hour, I finally made it. He’s had the car for more than 6 weeks now but has only recently spent time on it. When he first looked at it, guess what? He thought it was a fuel issue not getting to the front 3 cylinders. I asked him to do a compression test which had not been done by any of the previous mechanics. He called me and said he got around 100 on all 6 cylinders and did it twice (cold & warm). He didn’t seem concerned that they were all this low until I told him that everything I’ve read says the compression should be around 150. In fairness to him, he had a Haynes manual for the car but it doesn’t state what the numbers should be. If the numbers are all pretty much the same, that’s supposed to be a good thing, right? As a caveat, he said he wasn’t 100% sure his gauge was accurate. He threw out some possible causes: head gasket failure, or cam/valve timing issue. I read up on the cam/valve timing and came across timing chain stretch and asked him to check the slack while I was there.

[He did and it was approximately ¼” or less than 5 degrees. I also noticed that when the #1 piston was at TDC on the compression stroke, the cam sprocket was set to timing mark#3 which was at 11 o’clock and the groove was just to the right of the notch. I did not see any shiny link the manuals talk about but that may only pertain to when you’re installing the chain. Does this all sound OK to everyone?]

[While he was adjusting/checking the valves, he noticed the slack side of the timing chain would slap against the guide when he would crank the engine with a remote starter button, other times the slack was gone. He seemed concerned by this and wasn’t used to seeing this on other vehicles. Is this normal on “Z‘s”?]

He also noticed some water/coolant residue on a nut & bolt located just behind and to the right of the thermostat housing. It’s the same area that I’ve heard a slight hissing sound after the car is at normal operating temperature and I shut off the engine. He then raised the car on the lift and we could see residue/stains on the side of the block below. He said I might have a leaking intake/exhaust manifold gasket.

[He’s seemed to have dismissed the head gasket as a cause. I am not getting any coolant in the oil. Also, I checked for exhaust gas bubbles in the radiator and didn’t see any. I don’t remember having to add any coolant since the overheating issues were resolved. Is there any way my overheating episode could have damaged the head gasket or warped the head, causing the low compression #‘s yet I‘m not loosing coolant?]

If this hasn’t put everyone to sleep by now, I would greatly appreciate responses to the questions in brackets along with any other suggestions or questions. I would love to be able to drive my Z again and resolve this problem before I either run out of $$$ or time left on this planet.

[madkaw]

WOW- and I thought Ive had car issues- my condolences .

Fuel- did you or anyone pull out the fuel sending unit from the tank? The return or sending side could be plugged with junk causing pressure build or no fuel at times.

Cylinder head- get a new compression guage and do the test yourself- google the proper procedure.

Also, you can borrow a pressure tester from autozone to test for a bad gasket. It works pretty easy by just measuring the radiator pressure while the car is running. You can watch the pressure build and pull spark plug wires one at a time to see which cylinder is bad-- if the pressure is building.

Electrical- those years had a brain box for the ignition- right ? I would try and replace it. I think I have one of those that came off a late 73 240 that you can try if you can't find one.

Coolant- have you run any type of rust removal product or flush through the block?

[Bruce Palmer]

First thing i want to know: do you have flat top or round top carbs?

Pull the coil wire and fuel line to the front carb and have someone crank the motor to make sure you have gas getting that far.

In the float bowl lid is a fine mess screen called a "final filter" and it may be nothing more than it is plugged with crap from the tank after sitting so long which is disabling the front carb not all the time but some of the time.

Your write up was excellent but a little disapointing from the standpoint that that many guys who call themselves "mechanics" couldn't stumble on something that'd help solve the problem.

[AZ260Z]

WOW- and I thought Ive had car issues- my condolences .

Fuel- did you or anyone pull out the fuel sending unit from the tank? The return or sending side could be plugged with junk causing pressure build or no fuel at times.

Cylinder head- get a new compression guage and do the test yourself- google the proper procedure.

Also, you can borrow a pressure tester from autozone to test for a bad gasket. It works pretty easy by just measuring the radiator pressure while the car is running. You can watch the pressure build and pull spark plug wires one at a time to see which cylinder is bad-- if the pressure is building.

Electrical- those years had a brain box for the ignition- right ? I would try and replace it. I think I have one of those that came off a late 73 240 that you can try if you can't find one.

Coolant- have you run any type of rust removal product or flush through the block?

Back in 2003, first thing we did was to drop the fuel tank and send it out for cleaning, it's so long ago, can't remember inspecting the the sending unit.I'll definitely look into getting a compression gauge, so I can feel confident about the readings. Thanks for the tip on borrowing the pressure tester from Autozone. I was able to get (2) brain boxes(TIU's) and swapped them out, so I think I can eliminate that possibility. As far as the coolant, back in 2003 I drained the system, backflushed until it was clear, pulled the radiator and took it to a shop for repair. I didn't add any rust removal product, but on a tip from my old mechanic, made a screen filter and put it in the top radiator outlet to capture any rust particles and periodically would check and replace it. The amount of rust particles diminished to almost nothing. Guess it wouldn't hurt to add some rust removal product now? Do you have any input on the questions regarding the timing set up and slack in the chain as well as possible damage to the head caused by overheating? Thanks for your input and tips.

[AZ260Z]

First thing i want to know: do you have flat top or round top carbs?

Pull the coil wire and fuel line to the front carb and have someone crank the motor to make sure you have gas getting that far.

In the float bowl lid is a fine mess screen called a "final filter" and it may be nothing more than it is plugged with crap from the tank after sitting so long which is disabling the front carb not all the time but some of the time.

Your write up was excellent but a little disapointing from the standpoint that that many guys who call themselves "mechanics" couldn't stumble on something that'd help solve the problem.

When the problem first occured, I still had my flat top carbs, which were rebuilt as part of the restart in 2003. Problem first occured in 2006/2007 timeframe.I replaced them with '72 rebuilt SU's in 2008, thinking that would cure the problem, which was a costly assumption.

I don't know if the float bowl screen was checked by the "Carb Specialist", but I will definitely do that myself when I get the car back. Any other input on the timing set up/slack in chain or possible damage to head or intake/exhaust manifold gasket from overheating? You can't imagine how disappointed I am and have searched for a "Z" mechanic in the area but haven't been able to find one. Thanks for the tip/input.

[Zed Head]

How about a fuel pressure gauge installed so that you can check it when the problem occurs? A direct, immediate measurement as the problem is happening. Might help narrow the range of possible causes.

[AZ260Z]

How about a fuel pressure gauge installed so that you can check it when the problem occurs? A direct, immediate measurement as the problem is happening. Might help narrow the range of possible causes.

Good question, since the "carb specialist" is relatively nearby I will drive the car back to him and if it wasn't done, I'll have him do it. Thanks

[AZ260Z]

WOW- and I thought Ive had car issues- my condolences .

Fuel- did you or anyone pull out the fuel sending unit from the tank? The return or sending side could be plugged with junk causing pressure build or no fuel at times.

Cylinder head- get a new compression guage and do the test yourself- google the proper procedure.

Also, you can borrow a pressure tester from autozone to test for a bad gasket. It works pretty easy by just measuring the radiator pressure while the car is running. You can watch the pressure build and pull spark plug wires one at a time to see which cylinder is bad-- if the pressure is building.

Electrical- those years had a brain box for the ignition- right ? I would try and replace it. I think I have one of those that came off a late 73 240 that you can try if you can't find one.

Coolant- have you run any type of rust removal product or flush through the block?

Madkaw, Just to be clear, when you referred to the fuel sending unit from the tank, is it what the Haynes manual calls the Transmitter unit which is located to the left of the return nozzle?

[madkaw]

The fuel sending unit drops in from the top, it is what your feed and return lines go to on the tank. The reason I mentioned this was I had a 280zxt that would just basically die and then later clear up. Long story short, when I pulled the sending unit it looked brand new, but the return side was plugged with what looked like a petrafied bug.

Another mechanical adventure in my life with a problem similiar to yours was on a Ford Capri. A girl I worked with went to every shop and paid hundreds and hundres of dollars to try and figure her dying and loss of power problem. In the end it turned out that a mouse had been in her car and had ate away on the insulation on her wires under her seat-where the brain box went. The car would act up and then be fine. So I would make sure your grounds are good-especially stuff around your ignition. I'm leaning towards a wiring issue-unless that sending unit is plugged!

It seems that you have covered your basis well and I feel your pain. It seems like you have been diligent in finding this issue, I hope we can help.

Edited June 10, 2012 by madkaw

[AZ260Z]

The fuel sending unit drops in from the top, it is what your feed and return lines go to on the tank. The reason I mentioned this was I had a 280zxt that would just basically die and then later clear up. Long story short, when I pulled the sending unit it looked brand new, but the return side was plugged with what looked like a petrafied bug.

Another mechanical adventure in my life with a problem similiar to yours was on a Ford Capri. A girl I worked with went to every shop and paid hundreds and hundres of dollars to try and figure her dying and loss of power problem. In the end it turned out that a mouse had been in her car and had ate away on the insulation on her wires under her seat-where the brain box went. The car would act up and then be fine. So I would make sure your grounds are good-especially stuff around your ignition. I'm leaning towards a wiring issue-unless that sending unit is plugged!

It seems that you have covered your basis well and I feel your pain. It seems like you have been diligent in finding this issue, I hope we can help.

There's nothing showing on the top, I wonder if Haynes' lingo for sending unit is Transmitter unit? I'll look in the FSM and see if there is a better description and picture. I hope it's something like that also, because if it's electrical, I can look for chewed wires but I'll need to read up on how to check for good grounds.