Reality Check, Lazy man here(?)

[97SVX_SCV]

I hope I posted this in the right place...

97 LSi. 137,000 miles. P0400 code, "EGR flow malfunction". @ factory manual page 235 OBD-II diagnostic procedure 10AJ1, No P0105, p0106 P0403 or P1102 codes. Only P0400.

Used diagnostic connector to check electrical function of all underhood solenoids and fans etc. All -including EGR solenoid control valve- were OK operating electrically as verified by hearing clicking for each one.

Collector removed. All EGR lines intact but old. Some may have tiny blowby/leakby - could that small of a leak trigger P0400?

Next!

Found broken nipple to hose that routes to canister on Purge Control Solenoid Valve. Other nipple to collector is connected via three way (T) fitting to two pipe outlets that exude from beneath throttle body. (Noted and cleaned up lots of oily grit/dust right side engine compartment: seemed to be radiating from below canister.) This solenoid is run from manifold pressure and seems independent from EGR vacuum circuit, YET I MUST ASK: do I assume this 'nippular' damage induced during collector removal or could it contribute to P0400 code?

Also: very bad news for me...the Purge Control Solenoid is a discontinued part. "Part 16102AA020 not available". Anybody know of another part that might be retrofitted? In the mean time I will try to epoxy it back together.

Moving on.
EGR operates as verified by applying vacuum to EGR activation port. Is that kind of activation sufficient to verify EGR fidelity to eliminate as a cause for P0400 or is there other consideration?

Now as a level headed but LAZY man I ask: am I to accept that as long as everything is disassembled, I should unseat my lazy behind and remove/clean/replace the EGR and piping and hoses, the whole shooting match...

or is it better to reassemble everything with new/repaired Purge Control Valve and WITHHOLD FROM refitting new hoses in EGR circuit to be certain that other sneaky teeny leaks are the root cause? Logically. the cost to me of being right about the teeny leaks as the causation is that I have to do it all over again to replace the hoses anyway.

Should I just suck it up and assume everything is hosed and do everything listed as if by regal fiat, bureaucratic policy? It goes against my lazy nature: seems like overkill and imprecise.

Thanks in advance. Maybe I just talked myself into it, but still want to hear from the community. You know, for the humor and camaraderie of it.

[Blacky]

Go ahead and fix everything while it's apart. You'll thank yourself when the PO400 is gone (hopefully gone that is).

Fix the purge if you can but it should be unrelated to the EGR.

You will find that a lot of parts on these cars are NLA.

[TomsSVX]

The only thing that monitors the function of the egr is the temp sensor on the manifold so either the sensor is not reading properly or the passages are blocked with spot and there is no flow. This is all taking into account that you have tested the egr valve and verified it's physical operation. Happy hunting!

[97SVX_SCV]

Originally Posted by Blacky

Go ahead and fix everything while it's apart. You'll thank yourself when the PO400 is gone (hopefully gone that is).

Fix the purge if you can but it should be unrelated to the EGR.

You will find that a lot of parts on these cars are NLA.

Thanks for the opinion. I am also doing a detail cleaning with detergent and water and toothbrush while I am in there. I use a shop vac to vacuum out the muddy residue while rinsing with water from a spray bottle. Anything that is still there after that cleaning gets Q-Tip/Gasoline touch up.

I am going to unplug any available connectors and rinse contacts with electrical contact cleaner and then put a bit of dielectric grease on them before remating.

I am also CONSIDERING redoing the chromate on the fuel lines that mount on the collector to restore them back to the original yellow that has diminished over the past 23 years.

I ask about this stuff because I am in California and passing smog is a hard stop for registration here every other year (I am an odd-year smog check registrant, so, HURRAY, welcome to 2021!). It is exciting and challenging to amend things that have gone astray with the couple of old cars I have.

[97SVX_SCV]

Originally Posted by TomsSVX

The only thing that monitors the function of the egr is the temp sensor on the manifold so either the sensor is not reading properly or the passages are blocked with spot and there is no flow. This is all taking into account that you have tested the egr valve and verified it's physical operation. Happy hunting!

Thanks for the reply...Please help me a little more if you can.

Run that by me again? Which temp sensor?

I asked about the potential for the Purge Control Valve broken nipple because when that valve activates, it connects to the canister, or it would if the broken nipple wasn't broken

Here's my hypothesis:

When it is broken and not connected to the canister anymore, the valve is now open to a source of fresh clean California air downstream from the MAF and MAP and P and R connections to the BPT, injecting whatever amount of clean California air a 3mm hose can conduct into the intake manifold (the "collector").

The canister connection back to the fuel tank is via a two-way valve that meters some amount of vapor into the canister to balance pressure inside tank with atmospheric pressure, and in case of excess vapor in the tank, soaking carbon in the canister with the excess, to be sucked into combustion when Purge control valve activates (if the hose nipple isn't broken, that is.)

Without that connection, purge never happens, the two way valve gets frustrated, carbon in canister gets oversoaked, canister might even exude gasoline or gasoline vapor into the environment. Maybe that why I found so much fuel grit near/around/radiating from bottom of canister.

So I am thinking that small extra unmonitored (by MAP/MAF and downstream of BPT P and R connections) air being bypassed into intake/collector by the broken nipple might generate an out-of-range condition under low flow / low air volume conditions (q.v, idle, hot).

I hypothesize that the vacuum imbalance is because BPT activates EGR by comparing pressure at throttle body plates to EGR/Exhaust pressure and the open connection that would be routing to the canister is open to air and the manifold pressure is lower than it would otherwise be, biasing the P and R measurements, and resulting in an out of range at low flow/hot air. At the BPT, P is left cylinder bank pressure at throttle body, R is Right bank, except at high flow -more than 4200rpm- when the induction control valve opens and flow is shared by both sides.

I speculate this BPT leak would throw a P0400 code because the incidence of the CEL came as I slowed and stopped after more than 200 cruising miles at pretty much constant speed. MAYBE the EGR vacuum measurement remains in range because at flow above idle with open throttle (at idle, throttle plates are fully closed) the leakage via broken nipple is lost in statistical insignificance, but at low air flow / hot temp (low air density) it is detectable/detected.

One other thing: there have been a couple times when the vacuum inside the fuel tank was large enough that when I opened the gas cap I got sprayed with fuel from inside the tank as the fuel vapor in the tank vented to atmospheric pressure and dragged some liquid fuel with it as it rushed out of the filler pipe.

Thanks for listening.

[Blacky]

"One other thing: there have been a couple times when the vacuum inside the fuel tank was large enough that when I opened the gas cap I got sprayed with fuel from inside the tank as the fuel vapor in the tank vented to atmospheric pressure and dragged some liquid fuel with it as it rushed out of the filler pipe".

My '97 does this all the time. I think it's positive pressure though. I haven't investigated the cause. I open the tank very slowly and let the pressure release. No emission tests here thankfully.

[SVX_MY_BABY]

Soon after I go my car the dealer did a retrofit of some type to the fuel filler. Mine's a 92. It was a recall as I recollect but I haven't seen any ref to it in the published recalls on the net.

[97SVX_SCV]

Originally Posted by Blacky

"One other thing: there have been a couple times when the vacuum inside the fuel tank was large enough that when I opened the gas cap I got sprayed with fuel from inside the tank as the fuel vapor in the tank vented to atmospheric pressure and dragged some liquid fuel with it as it rushed out of the filler pipe".

My '97 does this all the time. I think it's positive pressure though. I haven't investigated the cause. I open the tank very slowly and let the pressure release. No emission tests here thankfully.

Oh, OK. thanks again for replying.

I guess, maybe your observation is different from mine. When I twist the gas cap, it goes 'sssssssssssaaaaooooohhhh' in the way that you can kind of tell the cavity is filling with air. Like when you open a can of Planter's or other vacuum packed stuff.

[svxnavyvet]

I just cut a intake in half and the passage for egr was completely plugged.

Originally Posted by TomsSVX

The only thing that monitors the function of the egr is the temp sensor on the manifold so either the sensor is not reading properly or the passages are blocked with spot and there is no flow. This is all taking into account that you have tested the egr valve and verified it's physical operation. Happy hunting!

[97SVX_SCV]

Originally Posted by svxnavyvet

I just cut a intake in half and the passage for egr was completely plugged.

It would be great if you included a picture of that.

[TomsSVX]

The sensor sticks straight up on the r/s of the intake all the way at the back. It is just off the egr supply pipe where it connects to the intake manifold. I would guess that the egr ports are plugged with soot not allowing any flow thus not temp change. The ecm realizes that and sets this fault. Might want to remove the intake and all egr pipes and have them cleaned by a shop with an ultrasonic parts cleaner. It's very common for diesel shops to have these as some charge air coolers and egr coolers will require this from time to time

[97SVX_SCV]

UPDATE: All fixed and no codes. Passed smog. Epoxy fix of Purge Control Solenoid valve. Replaced of old rubber hoses. I am drafting notes that might be helpful for others if they perform similar service. Here are some first impressions:

First, you can likely only affix the front fuel lines that are part of the collector assembly by having enough service loop between the forward and rear fuel line connection. The reasons for this will be explained below. There is a rubber hose connecting the front and rear fuel lines on the left side beneath the collector, and near where the Aux Air Control Valve is mounted to the block. Put a spiral loop into this hose when you reassemble the two fuel lines that are mounted onto the collector to give you some service loop (literally!)when maneuvering the two fuel lines relative to each other during collector/intake reassembly. There is no way to affix this hose while the collector is mounted in place so it has to be affixed before putting the collector in place.

If anyone says you should 'bend the fuel lines out of the way during disassembly' beware of this because I learned the hard way...bending them changes their relative location to the fuel rails and the place where they mount to the collector, and it makes refitting them particularly difficult since they are aligning in multiple locations. You may not be able to bend them back into suitable shape if you get very aggressive with bending things.

Also, the fuel pressure sensor is sensitive to the order to assembly. Its protruding pipe is nearly in contact with the fuel lines when the rubber hose is affixed between the two, so I found it best to mount the collector with fuel lines loosely affixed and then fit the rubber hose onto the fuel line. Then fit the fuel pressure sensor into the rubber hose and then affix it into place on the right side fuel rail with two mount screws. Then move to the left side where you will need to navigate the fuel lines around a water nipple that goes into the firewall. After navigating that into position, tighten down the fuel lines on collector to the fuel rail with two bolts. After all that, then you can tighten down the fuel lines with two bolts on the collector.

I will post the entire lessons learned soon. Here's some pix of before/after of the engine:
Before: grimy & dusty
20201125_135859.jpg

20201125_135850.jpg

After:
20210206_125732.jpg

After assembly:
20210209_133419.jpg
20210209_133448.jpg

[Blacky]

Nice job. Your engine bay looks like new.

[SVX_MY_BABY]

Wow. Job well done.