Rich Renix?

[slowrider]

So I swapped an 89 engine from a manual trans rig that just smogged into an 87 longbed MJ auto with a warn out engine and it fails now on hydrocarbons and carbon monoxide. The truck runs well and just made the 750 mile round trip for the Rubicon run getting 15 to 18 mpg on the highway burried in spares but it won't smog and has an erratic idle that's usually a bit high. The entire manifold and CPS stayed with the truck and worked well with the other engine despite the blowby it had; any suggestions for what to check?

 

[5-90]

HC and CO indicate running rich - so I'm thinking (mainly) engine management.

First things first - how old is the cat? Factory original? I have a funny habit of replacing mine with "universals" spec'd for BBChevvy, and they work just fine. Pass smog, too!

Vacuum leaks? Even with the manifolds coming over, if the manifold bolts were working loose, they're going to still be loose - unless you retorqued them while you were swapping. And, it's entirely possible that they could have been "knocked looser" by the work involved in the swap. Check 'em.

HEGO sensor? It provides feedback for fuel metering - if it's shot, the engine will run in "open loop" - which is, as I recall, a bit rich by definition.

MAP sensor? How old is the thing?

IAT sensor? TPS? Both issues that you might want to just handle.

Vacuum lines? Those stupid Nylon things get brittle with age, and usually want replacing. I posted the three part numbers you'd need from NAPA a few months ago - see if they're still there. Those part numbers were, as I recall, good for ALL RENIX 4.0L (1987-1990, A/T and M/T.) If you didn't get them to replace concurrent with the swap - SHAME ON YOU. You really should do goofy stuff like that automatically...

It's the "erratic idle" you mentioned that lean me toward the vacuum leak - they're fairly common on inline sixes in general. Does the idle settle down once you get the engine warmed up? If it does, that's probably another symptom of a "core" vacuum leak - meaning intake manifold mounting or possible throttle body and EGR valve mounting...

Just out of curiosity, what did you do with the old engine? The only thing I can think of that is different between M/T and A/T, offhand, is the TPS on RENIX engines - and the A/T TPS works with the M/T (you just have an unused connection with an A/T TPS on an M/T rig...)

5-90

 

[slowrider]

HC and CO indicate running rich - so I'm thinking (mainly) engine management.

First things first - how old is the cat? Factory original? I have a funny habit of replacing mine with "universals" spec'd for BBChevvy, and they work just fine. Pass smog, too!

Vacuum leaks? Even with the manifolds coming over, if the manifold bolts were working loose, they're going to still be loose - unless you retorqued them while you were swapping. And, it's entirely possible that they could have been "knocked looser" by the work involved in the swap. Check 'em.

HEGO sensor? It provides feedback for fuel metering - if it's shot, the engine will run in "open loop" - which is, as I recall, a bit rich by definition.

MAP sensor? How old is the thing?

IAT sensor? TPS? Both issues that you might want to just handle.

Vacuum lines? Those stupid Nylon things get brittle with age, and usually want replacing. I posted the three part numbers you'd need from NAPA a few months ago - see if they're still there. Those part numbers were, as I recall, good for ALL RENIX 4.0L (1987-1990, A/T and M/T.) If you didn't get them to replace concurrent with the swap - SHAME ON YOU. You really should do goofy stuff like that automatically...

It's the "erratic idle" you mentioned that lean me toward the vacuum leak - they're fairly common on inline sixes in general. Does the idle settle down once you get the engine warmed up? If it does, that's probably another symptom of a "core" vacuum leak - meaning intake manifold mounting or possible throttle body and EGR valve mounting...

Just out of curiosity, what did you do with the old engine? The only thing I can think of that is different between M/T and A/T, offhand, is the TPS on RENIX engines - and the A/T TPS works with the M/T (you just have an unused connection with an A/T TPS on an M/T rig...)

5-90

The MAP and cat are unknown entities as I bought the truck used and haven't delt with them yet so I may just do that. The IAT, TPS, CPS and vacuume harnesses are 6 mo old. What the hell is the HEGO sensor? I can't find any more vacuume problems but that dosn't mean much; those things are everywhere. The Manifolds stayed with each truck not each motor so it is possible it's coming loose but it has had the issue from the first turn so I don't think that's it. The idle dosn't settle down when it's warm. When looking for a leak and pulling vacuume lines one at a time they all caused a higher idle except for the one to the map sensor which caused the idle to slow and stumble until I plugged it back in. Thanks for giving it some thought.

 

[old_man]

The MAT sensor is a common culprit to an overall rich condition. Other possibilities are MAP and O2.

 

[5-90]

Sorry - HEGO = Heated Exhaust Gas Oxygen sensor. Standard nomenclature, and I often forget that I haven't gotten the Lexicon completed and posted yet...

I don't need to tell you where it is, do I?:laugh3:

Critical sensors to fuel management are MAP, IAT, TPS, HEGO, and CTS - roughly in that order.

MAP = Manifold Absolute Pressure sensor, on the firewall
IAT = Intake Air Temperature sensor, in the intake plenum
TPS = Throttle Position Sensor, on the front of the throttle body (for RENIX)
HEGO = Heated Exhaust Gas Oxygen sensor, in the exhaust manifold (below where all the pipes come together, above the collector.)
CTS = Coolant Temperature Sensor, on the driver's side of the engine block. NOT the one for the gage (which is in the cylinder head) or the Thermal Fan Switch (TFS) - that's in the driver's side radiator tank. OBD-I eliminated the TFS, using the SBEC to trigger the electric fan relay, and OBD-II uses a single sensor, with BOTH external functions driven by the SBEC (the indicator gage/light was driven off the CCD bus, and the electric fan triggered by an SBEC output.)

SBEC - Single Board Engine Controller. Also called PCM (Powertrain Control Module) and SMEC (Single Module Engine Controller,) it's Chrysler's answer to OBD. The RENIX system is "pre-OBD," which is something that causes me NO END of fun when I have to get smogged every other year (times five rigs now...)

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