Runs Like Poop in Closed Loop

[flint54]

As topic implies, when the nominal operating temp is reached (~200F), motor runs like crap,

which suggests a poor O2 sensor, even though it's fairly new (<5K miles) and OEM.

 

Curious if there are other inputs besides O2 that are ignored by ECU during open loop?

[skidoo_j]

http://www.pirate4x4.com/tech/billavist ... manual.pdf

[HOrnbrod]

http://www.pirate4x4.com/tech/billavista/PDFs/Jeep_Renix_Fuel_Injection_manual.pdf

He has an HO.

 

As topic implies, when the nominal operating temp is reached (~200F), motor runs like crap, which suggests a poor O2 sensor, even though it's fairly new (<5K miles) and OEM.

 

Curious if there are other inputs besides O2 that are ignored by ECU during open loop?

Virtually all ECU inputs are ignored by the ECU until the closed loop transition; the ECU uses a program stored in memory during open loop. Suggest you install an A/F meter to monitor the transition, and to verify the O2 sensor ECU input. Also check the codes.

[carnuck]

I've had that problem when the coolant sensor acted up.

[flint54]

Ok, finally installed a wideband A/F meter (autometer 3370). Installed also

the separate O2 sensor (that came with the meter), slightly offset from the

OEM O2 sensor (keep out of the stagnation region). This is fascinating to

watch this gauge. During warmup, it hovers around 10. After reaching

temp, it's right at the optimum 14.7, and stays there while moving. Now

here's the puzzle: When I come to a stop, quickly, slowly, doesn't matter,

the reading drops to 10 and stays there, even if I rev the engine. The longer

I'm stopped, the fouler things get. Once I sputter back up to speed, it's right

back to 14.7 where it should be. The TPS is new. The IAC is new (and bore

is clean). Vacuum and fuel pressures are spot on. There are no codes. If

I'm moving and floor it, it pulls strongly almost to 3800 rpm and then sputters

badly. Back off and all is well. Most puzzling.

[mountainman]

Sounds like a stuck open injector. thats super fat. should pretty much never see 10s AFR.

Pull your plugs and have a look, they may be fouled beyond saving.

You can drive along and shut the key off while driving.

Coast to the side and pull the plugs. See which one looks out of place.

If they are all fat.. then your after another issue thats causing ECU to go that fat at idle.

Bad FPR, bad MAP sensor, leaky line to MAP, etc.

 

Your makin me want to toss the wideband on my jeep now...lol

[HOrnbrod]

Yes, check the plugs for sure. Another think I'd try is checking the timing and advance. Hook up a timing light and verify that it's steady on the timing cover mark at both idle and advances steadily when increasing the idle to 2000-3000 RPM or so. I guessing it will be jumping all around at idle and steady at higher RPMs.

 

Didn't you have some distributor problems awhile back? :hmm:

[flint54]

Yes, I had a distributor issue, and replaced the whole thing.

Coil and wires also new.

 

The plugs, to my surprise, weren't really fouled at all, in fact

the ceramic was whiter than I would like to see. All six plugs

are identical.

 

I'll check timing again tomorrow, but last check it was on the mark

at idle and had smooth advance.

 

The injectors were very recently replaced, and the FPR is new

Hesco adjustable, and set per FSM.

 

Vacuum is excellent, but I've never touched MAP. It's about the

only thing I haven't replaced yet.

 

By all means, go for the A/F gauge. It's a lot more fun to watch

than the road.

[mountainman]

I know how you feel. I build carbs and tune carbureted engines and have my whole life. So the last 6 years or so ive been putting widebands on everything to help dial tunes in exactly.

It makes life 100 times easier.

No guess work and far less plug reads. :)

[flint54]

So, following up on this, after checking all suggestions I found

that three things were happening together. The timing was

steady, except for an advance pulse (maybe 20 degrees) about

once per minute. During that pulse, the RPM dropped about

200, and the A/F meter pulsed from the steady 10 to 15, then

back to 10.

 

I gave it all the thinking I had, and came up empty handed. I took

it to my local trustworthy garage, and they agonized over it for

8 days, telling me I had already tried everything they had in mind.

Then, in a stroke of brilliance (or sheer luck), they noticed that I had

the MAP sensor vacuum teed into some other lines coming off the

manifold. They isolated the MAP vacuum line directly to the manifold

and BINGO! problem gone. So, even though the manifold vacuum

was solid correct, the MAP wants a direct vacuum only. No telling

what the ECM was trying to do, but all is well now. A/F is locked onto

15, as it should be, under nearly all conditions.

 

And so now I can finally return to making things better instead of just

making it run right. Yaaa Hooo !!!

[mountainman]

:thumbsup: .......

[HOrnbrod]

Then, in a stroke of brilliance (or sheer luck), they noticed that I had the MAP sensor vacuum teed into some other lines coming off the manifold. They isolated the MAP vacuum line directly to the manifold and BINGO! problem gone. So, even though the manifold vacuum was solid correct, the MAP wants a direct vacuum only. No telling what the ECM was trying to do, but all is well now.

 

Glad you found it. :cheers: The MAP sensor is more sensitive to vacuum fluctuations than any other vacuum device. That's the reason the OEM vacuum line from the intake to the MAP is not shared. Also it should be a rigid plastic line which also helps maintain the exact vacuum to the MAP. The use of a flexible rubber hose to the MAP isn't recommended and can cause vacuum fluctuations especially on hard deceleration or WOT applications when the vacuum really changes fast.

 

A lot of newer vehicles now have the MAP sensor bolted directly to the throttle body to eliminate the vacuum tubing and maintain a steadier vacuum. This isn't possible in our rigs unfortunately AFAIK.

[cruiser54]

I eliminated the vacuum line from the TB to the MAP on both my Renix Jeeps. Ran one from the intake manifold directly to the MAP and tapped and plugged the TB opening with 1/8" plug. Had an extra hole in the intake where I had removed my IAT when I moved it to the air cleaner housing.