'91 missing and would like a second opinnion

[tccrab]

Originally Posted by ZR-1Mikko

before I pull the plenum one more time I have couple things I'm wondering if anyone would happen to have answers for?

So if I pull the injectors to check for leaks can I just connect the battery and turn the power on from the key to prime them or what would be another way to prime them?

Is it possible to ohm out the Dis module to see if it is failing? Or should I just borrow someones Dis and swap it?

With the plenum off you can pressurize the fuel rails and actually fire individual fuel injectors and see them squirting fuel.
With the battery disconnected, pull the yellow plug out of the ECM. This the one closest to the outside of the car.
There are 24 pins in the plug, 4 rows of 6.
Put the battery cables back on and turn the ignition key to the 'ON' position.
The fuel rail is now pumped up.
Using the following chart (is for '90 - 91's, others are slightly different) to determine which pin in the yellow plug goes to which fuel injector. For example, Fuel Injector 1 for cylinder 1 is Y1, position 1 in the first row of the yellow plug.
All you need to do to fire fuel injector for cylinder 1 is apply a good ground to pin Y1 and looking down the appropriate injector housing hole you can visually see the injector squirt fuel on top of the valve.
Use a very thin wire, nothing larger than a small paperclip.
DO NOT, I repeat, DO NOT use anything that is larger than the male pin on the ECM itself to ground out this circuit.
If you stretch the female pin inside the plug with too large a wire it will FUBAR the connection and it could take you YEARS and $$$ to figure it out and fix it!!!
(don't ask me how I know this, just accept it to be fact.)



Tom

[ZR-1Mikko]

so i finally got around to pull the plenum again and went to try to fire each injector individually from the yellow ecm connector and nothing happened. No fuel pressure and obviously no fuel from injectors. So I went and connected the yellow ecm connector back and was able to get the fuel pressure when I turned the key on. Looking down to the injector housings's none of them are leaking... How ever the fuel pressure goes up to about 30 lbs and starts coming down slowly right after I turn the power on. The car has new fuel pumps and fuel filter, so I don't see those being the problem. Talking to couple people we are wondering if it could be the Fuel pressure regulator leaking and causing the issues I have been having with the car?

I guess there is no way of checking if the regulator is bad? I just hate go buy a $200 part without knowing for sure...

[tomtom72]

Originally Posted by ZR-1Mikko

so i finally got around to pull the plenum again and went to try to fire each injector individually from the yellow ecm connector and nothing happened. No fuel pressure and obviously no fuel from injectors. So I went and connected the yellow ecm connector back and was able to get the fuel pressure when I turned the key on. Looking down to the injector housings's none of them are leaking... How ever the fuel pressure goes up to about 30 lbs and starts coming down slowly right after I turn the power on. The car has new fuel pumps and fuel filter, so I don't see those being the problem. Talking to couple people we are wondering if it could be the Fuel pressure regulator leaking and causing the issues I have been having with the car?

I guess there is no way of checking if the regulator is bad? I just hate go buy a $200 part without knowing for sure...

There is a procedure in the FSM for checking the regulator. Also, pull the regulator vacuum hose off of the plenum connection and see if there is gas in that hose, gas in hose = regulator N/G. Obviously make sure the hose is not collapsing under engine vacuum.

In the "driveability and Emissions" section chart A-7 has a two page diagnostic for the fuel system. Pages 6E3-A-28 is where it starts. Sorry my office phone rang...work interferes all the time. You may want to look over that chart and maybe look in the "Intermittents" section, 6E3-B-1. I know if you slowly pinch the return hose the FP should go up, and if you pincgh off the fuel feed line the pressure should hold. But those are only small parts of the entire diagnostic chart. I wish I kne enough to say you diodn't have to run the entire chart....but I'm afraid that I don't. Sorry.

Originally Posted by ZR-1Mikko

so i finally got around to pull the plenum again and went to try to fire each injector individually from the yellow ecm connector and nothing happened. No fuel pressure and obviously no fuel from injectors. So I went and connected the yellow ecm connector back and was able to get the fuel pressure when I turned the key on. Looking down to the injector housings's none of them are leaking... How ever the fuel pressure goes up to about 30 lbs and starts coming down slowly right after I turn the power on. The car has new fuel pumps and fuel filter, so I don't see those being the problem. Talking to couple people we are wondering if it could be the Fuel pressure regulator leaking and causing the issues I have been having with the car?

I guess there is no way of checking if the regulator is bad? I just hate go buy a $200 part without knowing for sure...

Mikko, if you need a regulator to check, I have one. I'll ship it to you, if it works pay then. If not return it.

The manual has a pretty good diag of this, and it is fairly simple to follow along. But I am thinking it is not the regulator, but maybe a checkvalve on the fuel pump. The section you need to be in is 6E3 Section A. There is a fuel System Diagnosis chart.

[ZR-1Mikko]

Thanks guys. I found the chart. Will be doing the diagnosis tonight and let you know what I find.

[ZR-1Mikko]

Well I'm officially going crazy with this thing.

After following the fuel system diagnostic chart I came to a conclusion that the injectors are leaking. How ever after testing the injectors like Jeff suggested I was not able to see any gas leaking from the tips of the injectors. So I just can't figure out what am I missing here... I can not find any gas leaking anywhere...
The only thing I'm did different from manual is that the plenum was off when I did the test. But that shouldn't affect the test should it?

I think someone is trying to tell me I'm not meant to work on this car and just drop it at local shop to see what they can get out of it...
Unless one of you guys want a round trip to Vegas and give it a try

[XfireZ51]

Originally Posted by ZR-1Mikko

Well I'm officially going crazy with this thing.

After following the fuel system diagnostic chart I came to a conclusion that the injectors are leaking. How ever after testing the injectors like Jeff suggested I was not able to see any gas leaking from the tips of the injectors. So I just can't figure out what am I missing here... I can not find any gas leaking anywhere...
The only thing I'm did different from manual is that the plenum was off when I did the test. But that shouldn't affect the test should it?

I think someone is trying to tell me I'm not meant to work on this car and just drop it at local shop to see what they can get out of it...
Unless one of you guys want a round trip to Vegas and give it a try

You might talk Ccmano to drive his 90 out to see you from LA!

[tccrab]

Since you've already got the plenum off, I'd yank the injectors and take them someplace to be flowed.
You never know, you could have a bad one or two.

TomC
'Crabs

[tomtom72]

Not to be a wise a$$ Mikko.....when you checked the injectors did you put a paper towel or tissue under them or did you just do it by eye?

I'm only saying that when ever I do anything on my fuel system, like R&R the filter I use a tissue at the connections to check for leaks. Found a slightly worn O-ring that way last weekend.

Okay, barring any leaks the results say injector leak....what do the plugs say? Also, I agree with TomC that maybe a flow/leak test is in order......If you are positive ( again not trying to be a wise guy ) your run thru chart A7 had no mistakes on your part. I do that alot, make mistakes using the charts.


Tom

I just had a BFO.....I remember another write up about a mystery miss that turned out to be one of the metal pipes on the in-tank pump/sender assembly having a hair line crack in the tubing. Sorry I didn't think of this sooner.

[Paul Workman]

Initially, the suggestions were in line with what I might have suggested, so I kept quiet to see what the results were. But, after reading the thread, a couple things come out which may be more the result of putting stuff in writing, so take this with a grain of salt, if I'm off base:

Troubleshooting: One of the deadliest traps one can get into is to assume something or another can't be the problem because it was recently replaced with a new item. I read this several times in this thread, and so I raise it as a flaw in the logic. A technique that has saved my bacon many times is to assume NOTHING about the condition of a device is known unless it is tested!! You might be well served to step back and then proceed to test functionality of components in question and forget about when it/they were replaced. (In fact, one of my new - out of the box - Airtex fuel pumps had bad check valve resulting in a failed leak-down test. I had to isolate the pump to determine the problem (more on that later, if you want - got pictures showing how that is done).)

The other is putting a scanner on it or a computer and data logging to see what is going on. Problems leading me to buying my own scanner stemmed from "no codes thrown" condition, yet ran like chit (and a "no problem found" from the dealer's mechanic) In one case one of the O2's was shorting out after reaching about 3000 rpm, but it wouldn't do it all the time. Try to run THAT down without a scanner! My point is, a scanner and data logging will show you what is really going on over 40 some sensor and readout results and time stamp them all so you can see the interaction.

Hope this doesn't sound "preachy". Just that I'm late for work - gotta run!!

Mo later if ya need.


P.