A.I.R system?? -have loss of power… code 43 for knock, and 44 for lean condition????

[scouthead]

As says the title… 1988 TBI 350- manual transmission means it got the AIR /smog pump stuff here in CA.

I drove the truck HARD earlier this week. Rocky trails/sandhills… in and out of low range… revved the motor good quite a bit. Things were running fine… we stopped for a beer.

When starting the engine 30min later -rough idle. Drove away in 4-low and left the play area. Get to open road and shift into 2high- immediately I notice how bad the power loss is- I’m working the throttle and slipping the clutch just to pull away in first gear on flat ground… then check engine light came on and ran even rougher. Then the light went away and it ran a little better again.

The Lights on the dash cluster went out… (there may be something up with the combo switch) lights came back on -repeated a couple times.
I made it home.

Visual inspection and everything looks in place. pulled codes
43-knock sensor
44 - lean condition

 

[scouthead]

I was surprised to see a code 44 lean condition- if anything there’s been a hint of rich exhaust smell for a while.

I’ve been checking things-
-good spark at all 8 plugs
-hooked up smoke machine and looked for vacuum leaks- couldn’t find any with that route.
-EGR is fairly New and seems to open and close correctly with a vacuum pump
-O2 sensor is fairly new and the truck idles bad and runs bad before it’s warmed up, so I’m not suspicious of the O2 sensor right now.
-coolant temp sensor was tested a few years ago and was in spec and functioning… there is still a defined difference between open/closed loop so I’m not suspicious of temp sensor
-there’s no water in oil/oil in coolant that I can detect
-no new noises from engine

 

[scouthead]

After pulling the codes and disconnecting battery to clear them, the truck ran WORSE. Checked timing- seems good. When I disconnect the advance wire it barely runs, but it appears to still be set at 0 base timing.

Suspicious of Idle air control valve- did the reset procedure with no real difference to how things are running.

Got to thinking that the smog pump/ air injection system might have issues and pumping air into the exhaust at all times? Causing the lean condition and if bad enough tripping the knock sensor??

 

[scouthead]

I found that the AIR diverter valve doesn’t hold vacuum. Is it supposed to?? When I connect a vacuum pump, the valve doesn’t hold vacuum. It does redirect air a bit bit, but just for a second before the vacuum bleeds away. This seems like it would have been BOTH:
-a small constant vacuum leak at the throttle body
-continuously pumping air into the exhaust.

I’ve got the diverter hoses off and plugged the engine side/capped the vacuum port on throttle body.

Initially it seemed to idle MUCH better, and I had high hopes. That slight rich exhaust smell is immediately gone. I let the engine fully warm up.

Took it for a test drive =low power, and immediately threw a check engine light. Both codes 43 and 44 again.

Parked it. The EXAUST is REAL hot now. I mean - cats are hot to begin with, but after a trip around the block, my skid plate is so hot I can’t touch it. Got about 3 inches of air gap there- Never been that hot before!

Yes fuel seems to be spraying from the injectors well. I haven’t checked fuel pressure yet, but it was good 4-5000 miles ago when this engine went back in

 

[scouthead]

The Cat is new- less than 2000 miles on it.

I’m going to pull the spark plugs and attempt a compression test just for the hell of it. Anything else I should be looking real hard at?

 

[Wes Harden]

if your cat is that hot, it may be getting to much unburnt mixture. Guessing aftermarket cat. It could also be backing up. What does a vacuum gauge say when reving to 2500ish ?
What does V gauge say at idle ?

 

[scouthead]

Well the vacuum gauge has been on a bunch of the hoses and devices, but haven’t had a reading while running yet… difficult now because after doing a compression test and checking a bunch of stuff (and disconnecting the battery) the damn thing will only idle for 10-20 seconds (and rough as hell) before stalling

Compression test was good- most cylinders 167psi
Highest was 170
Lowest 162

 

[Fastereddie]

I would definitly check the the fuel system pressure and volume.

 

[Wes Harden]

yeah my knee jerk reaction is vacuum leak, fuel pressure is a possibility. Look down the throttle bores with blades open, look for any gasket peaking out. If you see gasket you need a new base gasket. 2nd place that isn't obvious is intake gasket leaking from the lifter valley. If you can keep it running, remove pcv from valve cover squirt some brake or carb clean in the valve cover. If idle changes you have an intake gasket leak.
do not adjust the throttle rpm screw, it create more head aches if you do.
The TBI IAC passage may be clogged with varnish and dirt, causing the iac to not be able to adjust idle rpm. Like wise the throttle blades have ecm calculated air flow, dirt build up at the blades in the bore will reduce the expected air.
How old is this engine ? rebuilt ? if so how many miles ?

 

[scouthead]

yeah my knee jerk reaction is vacuum leak, fuel pressure is a possibility. Look down the throttle bores with blades open, look for any gasket peaking out. If you see gasket you need a new base gasket. 2nd place that isn't obvious is intake gasket leaking from the lifter valley. If you can keep it running, remove pcv from valve cover squirt some brake or carb clean in the valve cover. If idle changes you have an intake gasket leak.
do not adjust the throttle rpm screw, it create more head aches if you do.
The TBI IAC passage may be clogged with varnish and dirt, causing the iac to not be able to adjust idle rpm. Like wise the throttle blades have ecm calculated air flow, dirt build up at the blades in the bore will reduce the expected air.
How old is this engine ? rebuilt ? if so how many miles ?

I will take the fuel pressure stuff with me when I go back to the truck next week. Also I have duplicates of most of the sensors and control modules but not sure where the IAC valves went- will make sure to have one in hand in case I throw a parts fit

I did hook the smoke machine up to the pcv line and pumped into the throttle body… couldn’t find any leaks that way…
What you mentioned about The internal intake leak, and spraying into the valve cover is a REAL interesting idea. I would think a lot of oil would get sucked in? None of the spark plugs looked particularly nasty. Most looked like they HAD been running normally and then recently lean deposits on top.

Engine has had a long life and many prior life’s.
Once from the factory in a suburban -owner just added oil here and there and never changed it. Excessive wear/smoking and burning oil, and ridges in the bores. -then it was rebuilt by me many moons ago… baked and punched out .060 (my engine is a 5.9 liter now?) roller cam from a b-body lt1… lotta turd polishing in the TBI heads… intake punched out to match the custom bored throttle body…

Then years back when it had about 50K on it- there was an incident. I broke a couple piston rings -motor came out and sat on a stand for a while until the OTHER “temporary” “good used” engine spun a bearing…
Then this one got a cylinder honed and new rings on one piston… slapped back together- head gasket and intake back on… now edelbrock TBI intake with a factory TBI on top (the performance one got wear on the shaft and the throttle blades didn’t always close correctly)
Some shop ruined my flywheel… a new one was attempted to “match balance” to what was left of the old one…
Harmonic balancer spun and had to be replaced…
Let’s see… what ELSE has happened to this motor ????

In current version, it’s got 6-7 thousand mixed road and hard offroad miles.

 

[Wes Harden]

So heads have been milled, stronger case for lifer valley intake leak as the angles are off. Oil mist might be sucked in, but not as much as you'd think.
Recenty lean tips on plugs, could mean more air, or less fuel

 

[Blue85]

You may have plugged the cat. Easy way to tell is that the engine vacuum is normal when you first start it, then it decreases until the engine stalls. You would also get a lot of air rushing out if you pulled the O2 sensor.

 

[scouthead]

So heads have been milled, stronger case for lifer valley intake leak as the angles are off. Oil mist might be sucked in, but not as much as you'd think.
Recenty lean tips on plugs, could mean more air, or less fuel

So far, the only thing I’ve been able to confirm in chasing down this lean condition thing, is that the AIR bypass valve does NOT hold vacuum. I believe the diaphragm has been fluctuating, and pulsating air is getting split between the exhaust manifolds and the bypass/dump into the air cleaner. But the hoses have been disconnected and plugged temporarily while I figure this out.

 

[scouthead]

You may have plugged the cat. Easy way to tell is that the engine vacuum is normal when you first start it, then it decreases until the engine stalls. You would also get a lot of air rushing out if you pulled the O2 sensor.

Yeah- the cat was 900 dollars about 3 months ago- so if it’s already destroyed im going to be upset!!
But, it may be time to pull the o2 sensor during a cold start just to see if the truck will warm up without stalling immediately.

Going to check IAC valve and throttle position sensor more seriously first… but then the o2 sensor comes out, or I’m drumming holes in my exhaust

 

[scouthead]

So heads have been milled, stronger case for lifer valley intake leak as the angles are off. Oil mist might be sucked in, but not as much as you'd think.
Recenty lean tips on plugs, could mean more air, or less fuel

Also- side note about the angles of the dangles… years ago when I built this engine the first time? My machinist had a gasket set that he highly recommended as being the best bang for the buck as opposed to ordering the usual suspects out of a summit catalogue… I believe the brand is/was Corteco? Head gaskets and intake are MLS, and coated in an odd white sticky something…
He thought the gasket thicknesses helped compensate for a few thou coming off a deck or heads…

Anyway he bought in bulk and turned them out at really good pricing- I liked that the material between the intake runners was thinner than the castings… so gave me some room to port match, and also less chance of them being misaligned and hanging out into an airway like some of those fat felpro ones I’ve seen…

Anyway nobody seems to sell these gaskets anymore- this last time I had this motor apart I really didn’t want to tear the entire thing down- I was able to find someone on eBay selling 4.5 sets of my gaskets! They bought the inventory from a failed AutoParts store at an auction- didn’t know what the gaskets were or what they were for- they just grouped by part number and spit them out on eBay as fast as they could…

I think I’ve got enough now to build another one or two complete engines, and repair several others -Hope that covers me for any 350s I’ll have apart in the rest of my lifetime!!