Bad injector? High Fuel Pressure?

[wheels87k5]

MODS: Please move to "Injection Section" if necessary

Bad Injector: Yep

Coming home from the parts store, and while I was on a straight a way, I decided to punch it after it shifted to second to see if it would down shift like it should. And it did. By the time it had shifted to 3rd I had to slow down to make a turn and the blazer died. I shifted to neutral and tried to start it but no go. It would crank over but wouldn't start. I pulled over and started all my checks. First thing was to check the fuses. Both good. Then turn key to on, hear the fuel pump prime, and smell lots of gas.

The wife came to give me some help just in case I couldn't get it started. I had her turn key on but not start it so I could see the spray pattern. Well, there was a spray pattern but it was on the passenger side injector only and it was dumping a lot of fuel when you turn the key. The other injector just sat there. Nothing. I switched connections and same thing so I figured it must be a bad injector. Thankfully I carry a spare set of injectors and went ahead and replaced both of them. After a couple of cranks it finally started. Took her home and checked everything out and all seems ok.

So I'm guessing it was a bad injector. Eventually I'll have to swap the suspected bad injector to make sure but right now I'm nuts deep on a pontiac 400 tear down and need to get as far on that as possible.

Now, there have been a couple of times when driving the blazer it would just die. Wait for a minute and it would start right up. That hasn't happened in a couple of years but it still makes you wonder what caused it to die.


.

 

[wheels87k5]

Forgot to mention: I will post up once I do the injector swap to verify the trouble,

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaand, for Deuling, I'll post pics, in "Other Rides", of the said pontiac 400 tear down and the Y88 it belongs to. That will happen later tonight.

 

[wheels87k5]

I'm not quite sure what's going on but I would like to learn.

I am trying to test a couple of injectors. I want to check out the spray pattern on what's in there now so I put the key in and turn it to on, I do hear the pump (buzzing sound) but there is no fuel coming from the injectors. I started the blazer, let it run for about a minute and shut it down. Waited a couple of seconds, turned the key to on and hear pump, but still no spray from injectors.

And NO.....I am not turning the key to on and then hurrying to get up on the fender to see if there is a spray pattern. I'm not that fast.

 

[dyeager535]

I'm not quite sure what's going on but I would like to learn.

I am trying to test a couple of injectors. I want to check out the spray pattern on what's in there now so I put the key in and turn it to on, I do hear the pump (buzzing sound) but there is no fuel coming from the injectors. I started the blazer, let it run for about a minute and shut it down. Waited a couple of seconds, turned the key to on and hear pump, but still no spray from injectors.

And NO.....I am not turning the key to on and then hurrying to get up on the fender to see if there is a spray pattern. I'm not that fast.

Injectors don't pulse until the ECM "sees" the engine turning over through the DRP (distributor reference pulse). Start it with air cleaner off, and watch.

 

[wheels87k5]

On the first post, I stated that there was a spray pattern on only one injector when turning the key to on. Do you know what may have caused that?

 

[dyeager535]

On the first post, I stated that there was a spray pattern on only one injector when turning the key to on. Do you know what may have caused that?

If it was spraying when the key was turned on but engine wasn't turning over, injector was stuck open. I just assumed it was being cranked and one wasn't spraying at the correct time, not that one was spraying at the incorrect time.

Edit: I suppose there could be an issue where the - lead was shorted to ground. The injectors always have power when the key is in run/start, the ECM pulses the injector to ground to fire it. If the injector - to the ECM was grounded somewhere, it would fire. I believe TBI also used two injector drivers, so a continuity check to ground with the key off on that injector connector should tell you if that is the problem. Since you said the issue followed the wiring, not the injector (did I read that right?) that's the most likely problem.

Are the wires pinched from where they go under the air cleaner? That is a common problem.

 

[wheels87k5]

No...the wires aren't pinched. I checked for that and bad connections. All are good.

I just replaced both injectors with the ones in question. Blazer started right up so I don't think it was an injector.

When the problem was occurring, you just turned the key to on and only the passenger side would spray....and it sprayed a lot. I switched the connections and same thing. It might be what you were saying about a ground problem.

 

[dyeager535]

When the problem was occurring, you just turned the key to on and only the passenger side would spray....and it sprayed a lot. I switched the connections and same thing. It might be what you were saying about a ground problem.

If it was a ground problem, it's bound to come back. Those wires go straight to the ECM from the injectors, if they were grounding out, it is on the engine, body, some other ground, and it's coming from bare wire where there shouldn't be.

 

[wheels87k5]

Thanks for the help.

Just got done with dinner. I'm going to check those wires now. I'll post up any findings.

 

[dyeager535]

It could certainly be an intermittent issue, what you've done (not bad) may have caused the problem to go into remission (lol) and you might not be able to detect it now that everything is working properly. But you'll have an idea if you have problems in the future.

 

[wheels87k5]

It was a bad injector, along with other things that I'm slowly finding.

I had an issue with the throttle body port stem, for the MAP sensor, and so far that's been repaired.

I did a datalog and it shows that when I first take off it's running rich. BLMs were around 114. So I checked the fuel pressure and it's at 14.5 lbs. So I back it down but it will only go as low as 12.5 lbs. I tried a shorter spring in the FPR but same thing. I want to drop the pressure down to get more readings. Is it the spring tension that determines how much pressure? Does the diaphragm have anything to do with it?

 

[black dawg]

spring pressure against the diaphram sets pressure. What pump are you running? 14.5 down to 12.5 is a huge adjustment, I would leave it there for a while and then check block learn. I usually will see big changes in integrator and block learn with small fuel pressure adjustments that are hard to measure on a 1/2 psi increment gauge.

 

[wheels87k5]

The pump is an AC Delco. I thought that the low reading should be around 9 psi but it won't go lower than 12.5. I have 3 springs. They all read the same as far as the low pressure reading. I took one of the springs and cut off a small section. It is now running at 10.5 psi.

EDIT: MODS, please move to "Injection Section"

 

[dyeager535]

The pump is an AC Delco. I thought that the low reading should be around 9 psi but it won't go lower than 12.5. I have 3 springs. They all read the same as far as the low pressure reading. I took one of the springs and cut off a small section. It is now running at 10.5 psi.

EDIT: MODS, please move to "Injection Section"

12-13PSI is ideal for a stock setup. Most indicate that lower than that can cause noticeable issues in how it runs.

 

[wheels87k5]

Yeah, I agree with running it too low is not good. I just wanted to see a datalog with the different fuel pressures. My blazer is always running rich and I'm trying to get it tuned to match the small upgrades.

 

[dyeager535]

Yeah, I agree with running it too low is not good. I just wanted to see a datalog with the different fuel pressures. My blazer is always running rich and I'm trying to get it tuned to match the small upgrades.

I'd set it to 12-13, then tune from there. Should be running lean if the upgrades are increasing engine performance.

 

[wheels87k5]

I'll start with 13, since it's a lucky number, and go from there. I'll do a datalog and see how it looks. I'll also post it on here and see what needs attention.

 

[wheels87k5]

Will too much fuel pressure cause a rich condition?

 

[dyeager535]

Will too much fuel pressure cause a rich condition?

Absolutely, with caveats. The ECM is programmed with "X" lb/hr injectors as part of what it utilizes to come up with the pulse width (how long the injector is open). Injector Lb/hr is a calculation utilizing a specific pressure.

Making up some numbers, say GM rated your injectors at 13 PSI, and they flow 10lb/hr at that pressure. If you changed fuel pressure to 26PSI, they'd flow 14.1lb/hr. Therefore, the injectors are flowing more fuel.

Now, the caveats, with some more made up numbers. If your engine runs 128BLM's under all closed loop operations, and you increase fuel pressure a moderate number, it may push your BLM's down to 118 under the same conditions. That just means the ECM is taking fuel out (reducing how long the injector is open) to keep the engine at ~14.7:1 AFR. However, that is done with feedback from the O2 sensor. When the engine is cold, or under heavy throttle, the O2 sensor isn't used. So that extra fuel means the engine will be running rich...the ECM has no way of "knowing" there is extra fuel.

Whether you go with injectors rated for more flow, or increase fuel pressure significantly, it is pretty easy to exceed the capability of the ECM to adjust fuel delivery to 14.7:1 AFR under cruise conditions. if you've done that, you'd see a rich condition even with the O2 sensor working properly. You would see this in a datalog by the O2 never switching between rich and lean, and the BLM's maxed out.

It's ALL tied together, you can't just change one thing and not affect the way it runs. Even if you can't tell (like a mild cam upgrade, or bumping up fuel pressure) driving it, the only way to REALLY know how the engine is running, is to datalog it and see exactly what is going on.

 

[wheels87k5]

Got the fuel pressure set to 12.7 Did a datalog but windows 10 on this computer is missing the "send to compressed/zip folder" in the menu so I can't zip the file. Would you believe I have never zipped a file before. And when I want to give it a try the files to do this are missing? How else can I put that file on here?