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I am trying to find the problem with my car running rough and no power under load. It's a 75 Z and has run wonderfully for the 20 years I have owned it. I started with checking fuel pressure after the fuel filter. I have a solid 36 psi not running. Running it drops to 29 psi and steady there. It should be 32 I think. Is that much difference a problem? In checking the fuel pressure from the regulator I am getting 36 psi and again a solid 29 psi running. After I shut it down, I am getting very little bleed off of pressure, maybe a pound in an hour.
I guess for now, I am curious if the 29 psi fuel pressure while running is possibly a problem.

Additionally, here is what I have done to the car over the last few months:

1. Pulled injectors and cleaned them - all are functioning basically the same
2. Replaced injector connectors with new ones
3. Checked each connector for electric pulse
4. New fuel rubber hoses for the fuel rail and system under hood
5. New fuel filter
6. New water temp sensor
7. New Distributor Cap and rotor
8. New NGK spark plugs
9. New gas in the tank
10. I have cleaned all electrical connections

So now I am checking fuel pump and fuel pressure regulator and that is where I am at.
I'd appreciate any thoughts.

Thanks,
GT75Z
 

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I am trying to find the problem with my car running rough and no power under load. It's a 75 Z and has run wonderfully for the 20 years I have owned it. I started with checking fuel pressure after the fuel filter. I have a solid 36 psi not running. Running it drops to 29 psi and steady there. It should be 32 I think. Is that much difference a problem? In checking the fuel pressure from the regulator I am getting 36 psi and again a solid 29 psi running. After I shut it down, I am getting very little bleed off of pressure, maybe a pound in an hour.
I guess for now, I am curious if the 29 psi fuel pressure while running is possibly a problem.

Additionally, here is what I have done to the car over the last few months:

1. Pulled injectors and cleaned them - all are functioning basically the same
2. Replaced injector connectors with new ones
3. Checked each connector for electric pulse
4. New fuel rubber hoses for the fuel rail and system under hood
5. New fuel filter
6. New water temp sensor
7. New Distributor Cap and rotor
8. New NGK spark plugs
9. New gas in the tank
10. I have cleaned all electrical connections

So now I am checking fuel pump and fuel pressure regulator and that is where I am at.
I'd appreciate any thoughts.

Thanks,
GT75Z
Running fuel pressure should be between 36 and 38 psi. Pull the vacuum line to your regulator after the car warms up and see if any fuel drips out. This would indicate your fuel pressure regulator is toast.
 

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Discussion Starter #3
Running fuel pressure should be between 36 and 38 psi. Pull the vacuum line to your regulator after the car warms up and see if any fuel drips out. This would indicate your fuel pressure regulator is toast.
Fuel pressure not running should be 36 psi. From what I have seen, fuel pressure while running is less than that, being 32 psi. I have pulled the vacuum line from the fpr after warm up and it is dry. No fuel present. I can't find any problems with the fpr. I don't really want to throw $125 at a new one if that is not the problem. My next move is to do the tests out of the FSM. I don't understand a lot of those procedures but that is my only place to go now.
Thanks, GT75Z
 

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your FP is correct both running and not.
check the TVS see the FSM for the procedure.


I presume you checked the air filter?
 

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Discussion Starter #5
your FP is correct both running and not.
check the TVS see the FSM for the procedure.


I presume you checked the air filter?
So 29 psi is OK for fp while running, correct?
I will look for the TVS procedure in the FSM, thanks.
By Air Filter are you referring to the AFM? I have not run tests on that yet.

Thanks again,
GT75Z
 

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Discussion Starter #6
So 29 psi is OK for fp while running, correct?
I will look for the TVS procedure in the FSM, thanks.
By Air Filter are you referring to the AFM? I have not run tests on that yet.

Thanks again,
GT75Z
OK, I have not done this before and have a question on how to read the check procedures in the FSM. On the left side of the chart we have "Condition" on the right side we have "Check Item Number" and then we just see two or three lines starting with 1, 2 or 3 - followed by a list of numbers in parenthesis (see attached photo from the FSM). I understand that these are probably identifying ports on the 35 pin connector. But I am not sure what to do with them. Do I check each port for connectivity to ground? And if continuity does not exist, do I determine what element that number is relative too.
Also, when you pull the 35 pin connector, I can't seem to find anything that tells me which pin is #1 and which would be #35 .

Thank you,
GT75Z
 

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Discussion Starter #7
OK, I have not done this before and have a question on how to read the check procedures in the FSM. On the left side of the chart we have "Condition" on the right side we have "Check Item Number" and then we just see two or three lines starting with 1, 2 or 3 - followed by a list of numbers in parenthesis (see attached photo from the FSM). I understand that these are probably identifying ports on the 35 pin connector. But I am not sure what to do with them. Do I check each port for connectivity to ground? And if continuity does not exist, do I determine what element that number is relative too.
Also, when you pull the 35 pin connector, I can't seem to find anything that tells me which pin is #1 and which would be #35 .

Thank you,
GT75Z
I think I have the numbers figured out. Run the corresponding test if that number is shown for a condition. I got confused and didn't see that right off. Still curious about how the counting goes on the 35 pin connector.
Thanks,
GT75Z
 

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So 29 psi is OK for fp while running, correct?
I will look for the TVS procedure in the FSM, thanks.
By Air Filter are you referring to the AFM? I have not run tests on that yet.

Thanks again,
GT75Z

I am talking about the air filter. I assume its new and not clogged. always check the easy stuff 1st , its it getting air (air filter) is it getting gas (gas in tank) etc...
 

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+2 on the air filter and checking cheap, free easy stuff first. I would also pay close attention to the vacuum system. A leak in that system can call all kinds of havoc. What's your vacuum at idle and is the needle steady? 'No power under load' also suggests a malfunctioning distributor vacuum plate. Its common for these to get sticky and lose the little ball bearings they ride on after this many years. Traced a similar prob to a '76 I used to have and after fixing the difference in power was dramatic.
 

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Discussion Starter #11
Yes, the air filter is clean. I have never tried to measure the vacuum. What type of gauge do you need. Just looking at obvious things the vacuum seems to be good. But I will check further.
I am not sure what the distributor vacuum plate is. Is it inside the distributor? I just bought a new cap and rotor.

Thanks for all the info.
GT75Z
 

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was there some event that happened prior to the problem. It ran wonderfully for 20 years then (fill in the blank) now it lacks power. Was it a sudden loss, if so maybe something happened (cleaned engine/check something under the hood/had it serviced etc...) looking for clues.
 

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how do the new plugs look? pull them and post up a picture. did you check the temp sensor to see if the resistance is correct for the engine temp? The FSM covers the procedure and the temp/resistance curve.
 

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was all this done AFTER you noticed a loss of power


1. Pulled injectors and cleaned them - all are functioning basically the same
2. Replaced injector connectors with new ones
3. Checked each connector for electric pulse
4. New fuel rubber hoses for the fuel rail and system under hood
5. New fuel filter
6. New water temp sensor
7. New Distributor Cap and rotor
8. New NGK spark plugs
9. New gas in the tank
10. I have cleaned all electrical connections
 

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double check the connections of the water temp sensor and the thermotime switch both the sensor connectors and the bullet connectors to make sure you have them connected correctly. Checking for correct readings at the 36pin connector is the best way to know for sure.


Does your have the dual pickup distributor? if so make sure the water temp switch (not thermotime just a switch) is working, it is what swaps from one pickup to the other after the temp comes up.
 

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Discussion Starter #16
double check the connections of the water temp sensor and the thermotime switch both the sensor connectors and the bullet connectors to make sure you have them connected correctly. Checking for correct readings at the 36pin connector is the best way to know for sure.


Does your have the dual pickup distributor? if so make sure the water temp switch (not thermotime just a switch) is working, it is what swaps from one pickup to the other after the temp comes up.
In short, my car was in an accident. I had body work and paint done which took about 4 to 5 months and it was sitting. She has not run the same since. At first I added fuel injector cleaner and that helped a lot. She would still run rough for about the first 15 minutes and then smooth out to normal. I kept adding the injector cleaner and that did not help anymore but then I started developing leaks in the fuel line. One from the gas tank to the fuel pump and that just needed clamps tightened. Shortly after that a fuel injector hose started leaking and that is when I decided to pull the fuel system (to some degree), cleaned the injectors and put in all new rubber. So NO I was not losing power prior to the additions from previous post.

I have cleaned and checked the water temp sensor and Thermotime. I am going to check continuity at the 36 pin connector today or in the morning. I will also try the temp/resistance procedure.

I pulled the plugs and I am posting pics of them. Yikes, they are not pretty.
Also, I would assume I do not have a dual pickup distributor - not sure what that looks like but I included a picture of my old rotor if that tells you anything.

Thanks for the help,
GT75Z
 

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Classic rich run from temp sensor issue, OR wildly off distributor timing. If you look at the distributor do you see two pickups or just one? snap a pic of the dist with the cap off.


My money is on the temp sensor. maybe a incorrect hookup of the bullet connector or the plug to the sensor it self. the test at the 36 pin connector will tell.


a dual pickup will switch timing as the engine warms up IF the water temp switch is working (its prob not). however I don't think that would account for such a problem, but I don't really know since I have a single pickup.
 

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one other thing that is always a good idea


test compression and look for vacuum leaks


compression is always good just to know its ok


vacuum leaks are sneaky and can create all kinds of problem esp on EFI that does not use feed back to compensate.
a cheap and nasty way to check is get a smoke (cig, cigar, hooka) and plug up the intake at the entrance into the AFM (plastic cup works fine). take a puff and blow into the intake manifold (brake booster port is a good place). Look for smoke. Smoke is hazardous to the EFI health, just as it is to yours. so if you see any wafting out investigate. I had a leak where I missed putting an injector rubber seal back. Sometimes cracks in the tubing, disconnected hoses, all kinds of things can go wrong, esp if you disassemble something then put it back together.
 

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Discussion Starter #19
one other thing that is always a good idea


test compression and look for vacuum leaks


compression is always good just to know its ok


vacuum leaks are sneaky and can create all kinds of problem esp on EFI that does not use feed back to compensate.
a cheap and nasty way to check is get a smoke (cig, cigar, hooka) and plug up the intake at the entrance into the AFM (plastic cup works fine). take a puff and blow into the intake manifold (brake booster port is a good place). Look for smoke. Smoke is hazardous to the EFI health, just as it is to yours. so if you see any wafting out investigate. I had a leak where I missed putting an injector rubber seal back. Sometimes cracks in the tubing, disconnected hoses, all kinds of things can go wrong, esp if you disassemble something then put it back together.
Thanks Dave M. I need to check continuity on the water sensor. I will go do that in just a minute. I very likely have lost continuity.
I'll let you know. Attached is pics of my distributor, now I see what you are talking about and I am thinking it does look like a dual. I've got a vacuum meter coming tomorrow but I have heard of your technique for checking for vacuum leaks and I will try that while I wait. Should I use the larger of the tubes coming out of the intake going to the brake booster?
I can't imagine why my distributor would be wildly off, nor how I would diagnose that, I have never had the opportunity to learn that.

GT75Z
 

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Thanks Dave M. I need to check continuity on the water sensor. I will go do that in just a minute. I very likely have lost continuity.
I'll let you know. Attached is pics of my distributor, now I see what you are talking about and I am thinking it does look like a dual. I've got a vacuum meter coming tomorrow but I have heard of your technique for checking for vacuum leaks and I will try that while I wait. Should I use the larger of the tubes coming out of the intake going to the brake booster?
I can't imagine why my distributor would be wildly off, nor how I would diagnose that, I have never had the opportunity to learn that.

GT75Z
Can anyone tell me where pin 1 is on the 35 pin connector? My guess would be when looking at the connector, pin 1 is the upper right pin, at the end with the wire bundle.

Thanks,
GT75Z
 
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