87-91 chevy TBI issues, "Code 42"

[Vbb199]

Changed the knock sensor, took the truck on a test drive.
A hell ride.

Ran the hell out of it from stops, cruised for long periods of time at 55, took it down some back road locally Where's there's ALOT of curves with deceleration and acceleration couple straights running her hard and running 85-90 mph down the road.
.
No check engine light?
That was all in about a 15 min drive. Engine definitely was up to temp... Makes me wonder if the knock sensor was the issue or not.

Still kinda seems sluggish to me though.

There was a time and place where the big Bertha of a truck felt like a hot rod in town and on the freeway, accelerating and passing people was never an issue.

Idk. I just feel like that same substantial amount of power still isn't there.
Wondering if I should swap out ESC's and see if anything happens.

Even on hard downshifts. It just didn't seem like the power was there.

To be clear I guess, for a 1989 SUBURBAN to get up to 65+mph in 3 or so seconds isn't necessarily bad. I just feel like something is still stealing my thunder.

 

[Vbb199]

Those time frames and expressions don't make sense about "driving it for a long time" and the span was about 15 min....

Think I'm off on my drive time, but regardless, the general idea is given.

 

[Vbb199]

Curious on vacuum, I checked.
Motor makes a healthy, steady 55 in/hg

However, after just manually checking the EGR to see if it holds vacuum. It does not.
I pushed the diagram in, blocked off the little hole with my finger, and the return spring still allowed it to open back.
So no doubt the diagram must be busted.

That's DIAPHRAGM Damnit.
Not diagram.

 

[Vbb199]

That was pretty cracked out.
I said 55 in/hg.

I meant 22.5 or so. LMAO.

 

[bucket]

Lol, you had me confused with that 55 number. I was thinking it must have been some kind of newton meter measurement that I didn't know about.

The EGR system must be working? If it's not opening, it will normally set a code at steady speed 55+ or whenever coasting down from those higher speeds.

 

[Vbb199]

Lol, you had me confused with that 55 number. I was thinking it must have been some kind of newton meter measurement that I didn't know about.

The EGR system must be working? If it's not opening, it will normally set a code at steady speed 55+ or whenever coasting down from those higher speeds.

There on the gauge you can see the confusion lol!

Last night I tested the EGR solenoid, I got 40ohms, and I got 12v (whatever battery is) at the input of it. Solenoid no doubt works fine.

But I took the EGR, depressed it with my fingers, blocked off the vacuum hole, let off and it just expanded.
There's a leak somewhere in that diaphragm.

So I'll say the EGR does NOT work.
I may have to have driven it longer?

Drove it a good bit today. Never set any codes, nice healthy power coming from her.

But I know that egr is jacked up.

It's looking like im closing the gap on performance/engine health issues, other than the ****** thermostat that sticks sometimes.

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[Vbb199]

Lol, you had me confused with that 55 number. I was thinking it must have been some kind of newton meter measurement that I didn't know about.

The EGR system must be working? If it's not opening, it will normally set a code at steady speed 55+ or whenever coasting down from those higher speeds.

Today, from a dead stop, I romped down on it, and let off almost immediately after as the tires started to spin, just wanted to put a big load on the motor at temp and see what happened.... And then I heard it...

"Hissssssssssss"

The ECM must've commanded the solenoid open and when it went to pull a vacuum, because the diaphragm is broken, it started leaking air...

Which obviously map detects, then combustion Temps increase, causing pinging, retarded timing, etc etc etc.

I think that is my last issue.

 

[Vbb199]

If I get a chance today, I'm gonna "tee" my vacuum gauge in, and duct tape it down somewhere outside the truck so I can watch it.
Im willing to bet on heavy engine loads and 55 mph I'll see a drastic drop in vacuum.

 

[eric 87]

Funny thing is I just got my shipment from Summit yesterday to swap my TBI to carb. about 1000 in parts and yet here I am reading about MY code 42 that was the thing that tipped me over the edge to carb. I thought I had my issues resolved except for this erratic idling even though I have replaced everything at least one and tested every new sensor with a multimeter either on voltage to and fro or Ohms. And boom I still have idle issues but also now I have code 42.
again it is a problem I shouldn't have once I do the swap this week BUT it is sitting in my crawl that the TBI bested me. Such is life I suppose.

 

[Vbb199]

Funny thing is I just got my shipment from Summit yesterday to swap my TBI to carb. about 1000 in parts and yet here I am reading about MY code 42 that was the thing that tipped me over the edge to carb. I thought I had my issues resolved except for this erratic idling even though I have replaced everything at least one and tested every new sensor with a multimeter either on voltage to and fro or Ohms. And boom I still have idle issues but also now I have code 42.
again it is a problem I shouldn't have once I do the swap this week BUT it is sitting in my crawl that the TBI bested me. Such is life I suppose.

I would put holley a efi on this if I didn't want to keep it original in appearance, so I don't blame you

 

[eric 87]

I would put holley a efi on this if I didn't want to keep it original in appearance, so I don't blame you

original under the hood and the interior I think was redone in stock format to original colors according to RPO code and the body was white from factory. It is white but it is white pearl. You can see how I got in from the avatar picture. Those wheels are in the garage but NOT on the truck. I found a set of original rallies with a new set of Cooper cobras and put them on. But the rear bumper is gone and there is that roll pan of which will come off. Will be going to standard bumper and not step. I would have kept the TBI had it not just been giving me fits. And after I shot the parts cannon at it....the shop I took it to found the bad pick up coil. Every single item was replaced as I said before for the TBI. The idle never got corrected. And oddly before chasing the missing and popping it idled fine. But one minute it is about 700 idle and then BOOM it goes up on its own to 2500 which is half throttle or more. Two IAC's and they were tested later and it still did it. Then the code 42 was the kicker.
I will admit this for the fun factor. Code 42 is ignition module. I replaced even though it was entirely new Distributor. Other thing is fuel circuit most often the relay. Well I replaced TWO of the relays. Still code 42. Here is the funny
When taking apart the top of the engine I unplugged the ignition module. I was laying on top of the engine and I happen to catch 3 copper or gold pins inside a 4 pin plug. ONE of the pins or female half was GONE. So this is the reason for the code 42. IT was an open circuit. I bet when he replaced the distributor and unplugged it the plug lost that contact in it and it didn't make contact with the wire when he plugged it back in.
Too late and that would not have fixed the idle issue either.
Now I am trying to figure out if the computer has anything to do with the AC. Trucks in pre computer had AC without a computer so I know if it runs through the ECM there should be a way to wire without the computer.
I wanted to do all this wiring before installing the new intake carb and distributor since all that wiring is up at the firewall. Now would be the best time to do it. That and I want to rewire my entire fuel system while at it to get away totally from the computer. I will add a safety relay and use an electric pump back on the frame rail. I see there is a 3 way valve instead of the 6 way I have or is it 7.....anyway it will wire through the dash switch but I need to learn how to do that wiring circuit as well. THen it is a matter of putting it all back together. Just turning 60 I had thought I wanted to have old stuff so I can work on it myself. Been out of it for awhile. I can work on my 69 firebird. Easy to reach. This truck I am laying on the engine and rethinking my life choices lol! Once I get it all sorted I will take the very little body work before it gets bad and rusts through. I want to paint it myself !!! Maybe a nice pearl Blue. I know the original color is white and it looks fine. But there are so many white vehicles now especially trucks.
I want some color AND the interior is black and charcoal gray so it will go with any color. No black grey silver or white. Most reds would be out as well.
So a fuel circuit and AC if it is tied to the computer. I may end up ordering a complete harness for a much earlier year that had AC. And have them add a circuit for electric fuel pump. Then rewire it completely and have it done right.
These things are rolling projects though.

 

[wvsteveg]

I found out after 2 replacement distributors in my 87 V10 305 and after preforming all test in shop manual that some aftermarket ignition control modules arent compatible with the ecm-put original icm in replacement distributor and code 42 cleared and has not returned,been told ac delco icm is best