Jump to content
HybridZ

Rebuilt l28 engins runs sloppy, intake backfire, low feul pressure, BIG hesitation


Recommended Posts

Hi sorry for such a late response my phone was having issue with the website or somthing of that nature and wouldn't let me post!

 

ok so the timing is at 10 if I remember correctly, I installed a fuel pressure gauge that reads out to be about 28 psi then spikes up to 36 psi when reved.

yes it is fuel injected.

there are no vacuum leaks whatsoever

I also and went ahead and replaced the fuel filter.

also another thing I noticed is that when the hose to the top hat thingy on the fuel rail (I forgot the name) the fuel pressure stays at 36psi

also I had thought the injectors were bad but they looked to be in good working order.

when you start it up it runs as if it weren't firing on all cylinders then it will steady out to a normal idle. if you give it gas slowly it will rev up but if you give it gas fast the rpms completely drop then the engine will rev up but sputter in the process.

Link to comment
Share on other sites

The numbers look right.  Be aware that the PCV system is connected to the intake system.  A leak in one is a leak in to the other.  Described in the Emissions chapter.

 

Also note that many of the old AFM's run lean.  The sputtering is a sign, along with popping back through the intake system.  Adding a potentiometer to the coolant temperature sensor circuit will allow you to add fuel across the AFM range.  It works.  Don't mess with the AFM.

 

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

Link to comment
Share on other sites

  • 3 weeks later...

Ok guys so here is an update. the car is not running much better than before but I noticed that if I unplug the injectors one at a time #1 has no effect when unplugged meaning that Cylinder #1 isnt firing right? I noticed the problem and bought a new injector, distributor rotor and cap and new plugs but the problem is still there. The wires are fine too. What could the problem be??? I think this issue is a big part of my problems so I would like to get this out of the way first. Any help is greatly appreciated guys! Thanks!

Link to comment
Share on other sites

yes I have checked for spark and I am getting it on all plugs. The injectors are all firing correctly but they still seem to be acting up. The engine actually seems to run BETTER with injector #1 unplugged!?!?! The only other thing I think I should note is that the engine seems to not rev over around 3-4K I have a bad tachometer but I can definitely tell its not revving nearly high enough....All these weird problems has me thinking about switching to carbs!

Link to comment
Share on other sites

"there are no vacuum leaks whatsoever" How do you know this?

 

It seems like you're not even using the FSM, that gets mentioned endlessly on any Z car forum you can find.  

 

You can check if the injectors are functioning using a screwdriver and your ear, or a mechanic's stethoscope.  And some small Christmas tree light bulbs to check power pulsing.

Link to comment
Share on other sites

We checked for vacuum leaks with a proper vacuum gauge. Unless that isn't sufficient enough then there are no vacuum leaks that I have been able to find.

I have been looking through the FSM but I simply don't have enough time or money on my hands to go through every single thing in my car to check for a potentially small problem which is why I have decided it would be better to ask some people with more experience than me. As I said before all of the injectors are good and firing, your can easily hear them working and I have used a set of noid lights to insure that each was getting the correct power pulses. I even bought a new injector only to find that the other ones are in as good condition as the brand new one.

Link to comment
Share on other sites

Vacuum gauges don't tell you if there are vacuum leaks.  They only tell you how much vacuum is in the intake system.  Very general information, along with small details about variations between cylinders.  The simple tricks for ID'ing vacuum leaks are to remove the oil filler cap and see if the engine dies, or a vacuum hose and see if engine RPM changes.  You need a feel for how engines should run though to get much out of it.

 

You don't have to go through every single thing.  Just the things you're studying.  Fuel pressure, for example.  You said low pressure in your title, then reported some numbers, but didn't acknowledge that the pressure numbers were correct.

 

You said that you can hear all the injectors working but said above that you can tell #1 isn't.  So which is it?  Listening to 6 at a time is not the same as one at a time.  And you didn't talk about the noid light work.

 

These are the details that will make the difference.  

 

If you want to maximize your productivity when looking, look through the Engine Tune-up chapter and do everything described.  Could be that your valve lash is off.

Link to comment
Share on other sites

Sorry for my lack of info. Each individual injector is firing but cylinder #1 doesn't seem to be working properly. I am getting spark on all cylinders and each injector is firing, but cylinder #1 can have the injector unplugged and it wont effect the car at all. I will look more into vacuum leaks and the valve lash tomorrow. I'm sorry if I don't make sense sometimes but its a little hard for me to explain what is happening in words, I may take a video soon if the issue continues. Thanks!

Link to comment
Share on other sites

Alright so we kinda got the car to run properly. Here is what happened. First we checked the injectors and took them out to make SURE they were actually working properly, and they were. Then we checked the distributor,wires,spark plugs, and timing, and they all were good. Then we checked for compression and all my cylinders had about 170-180, Good. Then we adjusted the valve lash to correct specs so those are good. with all of this done the car still wouldn't run properly. We then today decided to take off the afm again and run some test, we made some adjustments and then closed the circuit on the water temp sensor because I thought it may be bad which is why it started smoking yesterday...BOOM the car ran properly for the first time since I had bought it! I let it run for awhile more then turned it off for a minute or two to move our other cars out of the way so I could drive it but as soon as I started it up again it had problems. so now the problem is that the car revs barely over idle (800rpm) then just kind of bogs down for the rest of the way. I am at a completely lost now :unsure: I am going to replace the water temp sensor and check the AFM AGAIN but that all I can think to do. I am pretty sure it is related to the AFM or some computer thingy but that's all I know for now. I will update soon with info but if anybody has had  a similar experience please share!

Link to comment
Share on other sites

We then today decided to take off the afm again and run some test, we made some adjustments and then closed the circuit on the water temp sensor because I thought it may be bad which is why it started smoking yesterday...BOOM the car ran properly for the first time since I had bought it! I let it run for awhile more then turned it off for a minute or two to move our other cars out of the way so I could drive it but as soon as I started it up again it had problems. so now the problem is that the car revs barely over idle (800rpm) then just kind of bogs down for the rest of the way. I am at a completely lost now :unsure: I am going to replace the water temp sensor and check the AFM AGAIN but that all I can think to do. I am pretty sure it is related to the AFM or some computer thingy but that's all I know for now. I will update soon with info but if anybody has had  a similar experience please share!

 

Try working through the Fuel Injection Guide.  You can't fudge your way throguh the EFI system.  You need to get everything set back to factory levels.  Might be too late for the AFM.

 

http://www.xenonzcar.com/s130/other.php

 

And work through the FSM chapters.  You haven't even confirmed that basic things like cam timing are correct.  Engine Mechanical chapter.

 

Who rebulit the engine?

Link to comment
Share on other sites

Ok I will look into it...I honestly have no clue as to who rebuilt the engine as it was already in the car when I had purchased it. Its practically brand new though. I have read that it says you can troubleshoot the problem via the 30 pin connector for the ecu? I will do all the test but is it a good way to find the problem or is it unreliable? It sounds like the most effective way to solve this.

Link to comment
Share on other sites

Alright guys I have decided that I am going to do the switch to carbs. I have had it planned out for awhile now but wanted to fix the efi first but because of all the trouble and cost I am going straight to the carbs. I will post in the parts wanted section but if any of you guys have a setup [triples or 4 barrell] I will gladly buy it off of you for a reasonable price. Thanks!

Link to comment
Share on other sites

That doesn't seem particularly wise until you figure out if it was purely EFI based. My initial thought is timing being off, enough fuel gets in there you can diesel the car for a few moments which may sound like it is running. Firing order is another simple one that comes to mind.

 

If switching to carbs be mindful of the pressure requirements, you have to swap out the fuel pump and such.

Link to comment
Share on other sites

Just had a strange thought. Did you install the distributor?  I once had a friend help me in stall my engine and he installed my distributor 180 deg off. It bolted up fine and was close enough to run but not well and wouldn't rev. Flipped it back and it ran perfect. The rotor still pointed in the correct position but the contact for each cylinders where not in the right spot. This was on a turbo distributor. Not sure what you have. 

Link to comment
Share on other sites

Yeah I have been looking into carbs for a while now and even if the problem is something else it would save me a lot of time to know that the air/fuel mixture is already correct. almost every single connector in the EFI system was severely corroded. The connectors for the fuel injectors were so bad that if you wiggled them they would go out on you. The carbs have been an upgrade I would have made either way but because of how troublesome the EFI is on my particular car I am switching now, and yes I am aware of the fuel pump and other things...believe it or not I do research a lot ;)

 

I didn't install the distributor on my car it was already installed but I will look into that! I probably will have to get some work done to it anyways if I can afford some triple webers, I think if I read correctly you have to get it modded to allow the webers to run perfect.

Link to comment
Share on other sites

You can just run ether to bypass the fuel system for the time being if that is a concern. I hear you on the corroded terminals, that could be problematic to chase down. Just an FYI going carb is not necessarily an upgrade per say EFI with a tunable computer and a TPS instead of the AFM will deliver much more uniform performance across the board, but as you say, if the connectors are all shot then a carb car has more power then a non running EFI car.

 

Just wanted to make sure you weren't planning on putting on carbs and regulating the stock pump down, more then one person has thought that would be ok. 

 

The 180 off is common, but the fact you said it ran makes me think a little otherwise. Just check that the distributor is pointing at the first cylinder and pop the oil cap off and see if you can see the lobes pointed up on cylinder one. Then it is 153624 from there. 

 

It really seems like the firing order is off if it is backfiring out the intake or timing is way off. You can get timing lights with RPM read outs pretty cheaply or you can buy a cheap eBay gauge for the RPM as well. 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...