Car is an '89. Performing typical leaking intake gasket replacement at about 61000 miles. Putting in rebuilt stock spec injectors recommended from FIC. Also new fuel pressure regulator diaphragm. Fuel pump is new. O2 sensor is new. MAF and relays are new. Car started and ran fine before this work.

My trusted mechanic tells me the system is dumping fuel and back firing. Won't go into close loop. He's letting it cool down for a bit and then will try again.

Any words of wisdom? Does to the computer need more time to adjust?
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are you sure that the new pump is rated the same as the old pump ?

 

What is the fuel pressure? IDK what the stock pulse width for your car should be but someone who does programming might be able to. What does the scanner say the CTS reads? Does it hold pressure at the regulator?

 

Good question and I don't know. It's a Delco part EP375 labeled as NOS. I can only assume it is correct. I measured fuel pressure at the rail after installation and it settled in between 40 and 45 if memory serves. I didn't have any issues at that time.

Could my man have installed the pressure regulator diaphragm incorrectly? Something else unplugged?

What would cause the injectors to spray too much?

It feels like he has missed something. This is/was a straightforward job. I was going to do it myself and don't have the time.

 

Shouldn't matter. Since we are discussing too much fuel and not a lack. This is what the fuel pressure regulator does, sends excess fuel back to the tank in the return line. Having too big of a pump shouldn't change anything... a set volume (Rail and fuel line) with a regulated pressure should not change anything unless the pump is so large it is overcoming the open to take line.

With that being said, the first thing that needs to be checked is fuel pressure. This should be checked first with Key On, Engine Off (KOEO). This should reflect maximum pressure since there will be no vacuum. 89 MAF car should be close to 43.5. Injectors - even "Stock Spec" are rated in supply poundage at an operating pressure. The computer is set with a constant (Flow Rate) to calculate the opening time (pulse width). If pressure is high, the computer thinks you have 22lb injectors, but you are running a high fuel pressure you will get too much fuel.

Now, if the "too much fuel" is just a little too much, overtime the computer will learn this and pull fuel in the BLMs. A fresh set up will not have done this, yet. Older injectors not flowing well enough or a FPR that is letting the pressure drop will get corrected in the BLMs as well by the addition of fuel overall.

Now, being that the computer has stored memory from when the system had old components, has it been reset? Have you checked the fuel pressure? Is the return line free flowing? Also, "New" doesn't mean "Good". MAFs are notoriously known for not working on many make and models. Especially remaned units.

Why did you replace all of this because of an intake gasket? Was there any reason to believe the other components were bad? Was the car running poorly before? If the other components were good before, I would be putting them back on before troubleshooting further.

Do you have a scan tool of any sort?

What is the IAC doing during all of this that is supposed to be controlling you idle? Is it functioning?

 

Hi, aklim.

Just got off the phone and he says fuel pressure is "within specs". They are closing up now and so I will get with them on Monday.

 

Assuming that it is 43 psi, does it hold pressure as Kyle mentioned? Obviously we can't test WOT in this state. Have him scan and see what the ECM is thinking is going on especially with the CTS. Pull the MAF and see if it works better. Is the timing within spec? How is your timing? Is the balancer moving?

 

Nice response, thanks!

The new parts are one's I have done over the past 20 months or so of my ownership. Not related to the gasket job -- I just wanted the situation clearly described.

As i mentioned in aklim's post, the guy is confident fuel pressure is within specs but he is still stumped. They are shutting down for today and will get back to it Monday. I'll post any resolution we find.

 

Lets say he is right. What does the ECM thinking is going on? I had my injector fuse shorted out once. This was because the left bank got crimped under the VC. Well, that bank wasn't firing so the O2 sensor thought it was lean since it doesn't know what the other side is like and will ASSUME all is good. The pulse width became 2.8ms and it smoked and sputtered.

 

All good stuff... did I miss where it was clarified how the car was running before?

Also, I will tell you this. We are going off what your mechanic says, but not what you are saying. How does he know it is spraying too much fuel? Is it because he can smell gas?

When my L98 Iroc sprung a leak on the rail... it would idle like crap if I could get it to start at all. I could smell gas... and then I found it. A leaking O-Ring at the 9th injector port. Just an "outside the box" thought. If one of the o-rings were damaged while he was putting everything back together, he may think it is rich because he smells gas and that the car is running crappy because it is rich. When actually, it could be horribly lean and gas is running down the back of the motor or pooling on the intake.

I don't like the answer "In-Spec". When I get answers like that, I feel like someone hasn't actually checked yet and just covering their *** until they do. I would want a number from them to know.

 

 

Its backfiring? sounds like he F up the timing.

 

 

How? He would have timed it, or so I would think

 

Could have done it wrong, maybe forgot to disconnect the ESC wire?

 

I keep checking this thread to see what the garage said.

 

Anything?

 

The shop is putting the original fuel injectors back in this morning. I will know more in a couple of hours. They are stumped.

 

I picked up the Vette yesterday afternoon. The shop didn't get around to putting back in the original Multec injectors until this past Monday. I haven't been pushing on them hard since I like the shop and I feel they do a good job on my other cars. The specific mechanic has owned an '85 and an '87 so he sounded like he knew what he was doing.

The car runs fine now. Timing is set well and the thing idles as new. As outlined earlier, when he started it up with the rebuilt Bosch units, fuel just poured as if they were all stuck open. They report gasoline spitting from the exhaust. Fuel was in the crankcase so they changed the oil and installed a new O2 sensor.

So, the mystery continues. Double checking the injectors from FIC, they are labeled as 22 pounds at 43.5 PSI. The orange Bosch 3 units. I am contacting them today to see what may have happened. Thanks to everyone for the comments.

 

If they are open then you have no pressure soon shut down and it won't build pressure since it quickly bleeds off. 1 failure, sure. 8? You probably have better odds with the lottery.