Miss fire and lots of smoke

[Danpatters583]

Recently replaced the fuel pump due to long start issues on my 1990 Buick reatta.

 

Did a tune up, and everything was acting great! Drive to the auto parts store and then it wouldn't start. Now it will start if I light depress the throttle but miss fires and spew a bunch of black smoke.

 

Here's what I've checked:

 

1) fuel pressure is good. 40ish lbs on prime. 

2) TPS shows accurate voltage in idle and when depressed

3)spark is good according to inline tester off the coils

4) iac is clean and new. 

5) grounds appear to be good. Cleaned up a few years ago and seem to be fine still. No voltage drop across any grounds.

6) only checked one injector for pulse but appears to be getting an injector pulse

 

here's what I've replaced so far

 

1) icm (Delco) and coils

2) fuel pump and regulator and filter

3) spark plugs (AC Delco rapid fire #14 set to .060)

 

 

Any help or ideas would be greatly appreciated!

 

on a side note, I've noticed a drop in vacuum to the fuel pressure regulator. Is it possible for that vacuum tee on the back of the throttle body go bad?

 

[Ronnie]

1 hour ago, Danpatters583 said:

fuel pressure is good. 40ish lbs on prime. 

Sounds like raw gas is flowing into the intake manifold for some reason when the engine is off. How fast does the pressure bleed down when you turn the pump off?

[rogold]

Could be the fuel pressure regulator has an internal leak, causing the attached vacuum line to suck gasoline straight into the throttle body.  or a leaky fuel injector dumping gas directly into a cylinder.

[Danpatters583]

It seems to hold pressure for a while. Doesn't seem to drop very fast. I swapped out fuel pressure regulators with no change. 

 

I've read on other sites with different cars, that a PCV valve can cause similar issues. I've never had that experience. However, I haven't replaced the PCV valve either... Have you guys ever experienced that?

Edited April 2 by Danpatters583

[Ronnie]

Usually a defective PCV valve or connection to it will cause a lean mixture. That shouldn't produce the black smoke you described. Black smoke is produced by a overly rich mixture or fuel puddled in the intake manifold that has to be burned off when you first crank the engine.

[rogold]

Did you get a few sparkplug wires crossed? Thats the only other thing I can think of.

[2seater]

Unplug the MAF and try it.

[Danpatters583]

Thank you guys. I will try all the above and double check the wires. I'll report back with what I find when I get home!

[Danpatters583]

So I double checked everything. Everything was good. I tried pulling off the connector for the mass airflow sensor and it started running! Swapped a new one in and so far so good.

 

But I'm curious, what is the acceptable reading for a mass airflow sensor? According to the onboarding diagnosis thing on the car it appeared to be working. Which is why I didn't expect it to be the problem. So I'm a bit confused but happy at the same time! 

[Ronnie]

4 hours ago, Danpatters583 said:

So I double checked everything. Everything was good. I tried pulling off the connector for the mass airflow sensor and it started running! Swapped a new one in and so far so good.

 

But I'm curious, what is the acceptable reading for a mass airflow sensor? According to the onboarding diagnosis thing on the car it appeared to be working. Which is why I didn't expect it to be the problem. So I'm a bit confused but happy at the same time! 

I've experienced the same thing myself. In my case it started out as a poor idle before the engine went into closed loop. I caught it before it progressed to the point the engine wouldn't run by unplugging the MAF and saw that it improved the rough idle. This happens so often that unplugging the MAF has just became a routine part of troubleshooting a poor running Reatta engine.

 

Just like testing the fuel pressure and looking at the ICM for the green/gray goo on the side, disconnecting the MAF to see if it improves how the engine runs is just something you learn to do. Just checking the MAF readings in diagnostics undoughtedly doesn't tell the whole story of what is going on inside the MAF.

[2seater]

Things like that are sometimes frustrating because a sensor can work, but be out of range enough to cause trouble, and not set a code. The nice thing about the GM programming is there is a backup or default setting baked in that will take over if the signal is lost. It will be a safe setting although not optimal. It works for almost all of the operational things on the engine, except the ICM of course 😊

[Danpatters583]

On 4/4/2024 at 11:51 AM, Ronnie said:

I've experienced the same thing myself. In my case it started out as a poor idle before the engine went into closed loop. I caught it before it progressed to the point the engine wouldn't run by unplugging the MAF and saw that it improved the rough idle. This happens so often that unplugging the MAF has just became a routine part of troubleshooting a poor running Reatta engine.

 

Just like testing the fuel pressure and looking at the ICM for the green/gray goo on the side, disconnecting the MAF to see if it improves how the engine runs is just something you learn to do. Just checking the MAF readings in diagnostics undoughtedly doesn't tell the whole story of what is going on inside the MAF.

So I've learned! I do have a weird miss fire at high speeds. Like 70mph or so. It ses to go away after a while but I've always had it. Doesn't seem to matter what type of coils or icm I install.