What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Exhaust that will choke a horse!

TommyD11730

TommyD11730

1/2 ton status
 Premium
Joined
Oct 3, 2014
Posts
454
Reaction score
51
Location
NY
Ok the particulars, 91 K5 GM reman 5.7 TBI with all emissions intact. Has possible 180 stat as the motor runs cool (open loop). Aftermarket singal exhaust with aftermarket cat (rattles). Engine runs and drives A-OK with no misfire.

I'm thinking as its running cool all the time were in open loop (rich) most of the time. Coupled with a sick cat (rattles) that isn't helping things.

So I'm wondering. I'm going to replace the exhaust and loose the cat. Does anyone think the horrible (it's real bad, worse then any old car) smell will improve?
 
Getting rid of the cat will worsen the smell, unless your cat is so old that it's not even functioning or something. Putting on a new cat will help the smell, but the better solution would be to figure out why it's running rich and fix that instead. Your gas mileage will improve.
 
You need to get rid of that thermostat. It's a bad idea to run one that cool in any case, doubly so with TBI where it is going to add extra fuel to try and warm it up to what operating temp SHOULD be (195*).

Loosing the cat is bad idea in terms of smell, cats make a large difference when it comes to obnoxious exhaust. A properly running vehicle won't smell much, however under certain conditions they do tend to stink, and a cat helps then too.

The factory "pancake" converters were garbage, they did not flow well at all, however an aftermarket high flow converter (which is pretty much all of them today) will not be a noticeable restriction to power.
 
List up the service number & prom ID. I will tell you what and how its running.

180 will still allow closed loop. I think the cats are a big part of the smell especially with full emissions. High flow cats do not light off like the old school ones.
 
I'm guessing the ECU is in the passenger kick panel? The Prom under the cover of the ECU and no way to scan a number Vs pulling it by eye.

Truck also has some rpm activated pcv valve. It's in theory better then the standard metered oriface in a plain old pcv valve. No clue about this one.

I'm going to fill up today and check mileage. Figure it should be what 12-15MPG?
 
stock cat would be pancake //pellete can should never rattle.

so you have a replacement style most likely . most of them are low quality and crap out these days fast if you don't buy a PREMIUM unit.

and ya 180 stat will work but just do the 195 unit . and if you don't know how old it is = time to change that hard working little guy out .

87-91 square body computers in under glove box . remove 4 7mm hex screws from glove box hinge and remove whole unit . then 10 mm hex bolt for lock down tab ub under dash pad / a/c box area and computer come right out .

2 small 7mm if I recall hex for cover to prom and just read the sticker .
 
If it's running open loop, not arguing that the 180* will force open loop, but it isn't going to help. I don't know about anyone else, but my engine temp will run under the t-stat rated temp especially under light load with the vehicle moving. Part of that is just going to be the poor quality of today's parts I'm sure.

Don't the TBI ECM's/PCM's compensate fueling based on temp throughout the range, even in closed loop?
 
If the cat rattles and it's clear externally that it's not the heat shield, it must be broken inside and should be replaced. I would argue that it will never smell good without a cat, but an old/bad one can be smelly too. Universal high flow cats are really cheap anymore. They don't work perfect, but it's a lot better than no cat. And the restriction isn't so bad.

Plus, the early style cats really relied on the air pump - and who wants to repair/replace one of those if there's ever trouble?
 
Just to be clear it's an aftermarket cat, the pancake OEM style is LONG gone.

I checked the MPG today and with mixed driving I'm getting 12 MPG with the only mod being 31" tall tires.

The temp I'm estimating based on the factory gauge mind you.

I think I'll start with the basics, complete tune up, and change out the stat. Check the timing and replace the filters (oh and make sure the trap door is open on the air filter housing). Oh yeah and ditch that $&@!! Electronic PCV for a factory one.

Funny I have driven Ford Trucks my entire life so it's hard getting used to seeing this in the driveway!

image.jpg
 
Team208Motorsports said:
List up the service number & prom ID. I will tell you what and how its running.
Click to expand...

Hey Guys Have not had much time to work on the K5 at all. However today I broke out the (old) scanner and had a look.

Wow, can’t say I have looked at a data stream from pre OBDII in some time. First, not sure if this answers the Prom question but the ID per the scanner is 6301. Is that enough information or do you need me to physically look at it for another number?

The truck is in fact running closed loop, at about 165F it switched into it. Best I could get out of it temperature wise was just under 200F. I have a stat and gasket coming tomorrow.

O2 reports the usual lean/rich slow rhythm you would normally see on these older trucks. The only thing I saw “odd” and I can’t recall if this is normal or not is the TPS @ WOT is only showing 80%. At curb idle it’s 11%. Throttle response is good so I’m not too worried about it. So that’s about it for now.

Hopefully I’ll have some wrench time this weekend.
 
Don't think any of the BCC's (Broadcast Codes) were numbers. Have to look at the PROM for the BCC, that vintage should be 4 digits, like "APYP".

Believe most can be read just by taking off the PROM cover on the ECM.

Edit: Huh, looks like it can be cross-referenced: http://www.scotthansen.net/BCCLookup.pdf 6301 is listed there, looks like the correct application to me, which would be BCC ARJU.

As with gear ratio/RPO tags, at this age unless original owner, I like to make certain, but if the scan ID is 6301 and the table is right, ARJU should be it.
 
82355 said:
Electronic PCV?

Martin
Click to expand...

Yep, that's whAt I said. I'll shoot photos after I remove it however it looks like they meter the vacuum to the valve via tach sig.

Truck came from Cali.
 
Oh and what's with the .035 plug gap?? It's electronic for goodness sake!
 
That'll work. As stated 6301 brings up ARJU. I'll grab the file and post up some shots.

Right away though I see ARJU is a California Emissions BCC........
 
All right. I pulled your Bin file up and compared it to a non Cali emissions tune. Lets go through the differences then I'll get into a little performance.

1) Main Spark table is 3-5 degrees lower in the general cruising area. 40kpa-60kpa / 1200 rpm-1600 rpm. At idle you are about 16 degrees as long as the dizzy is set right.

2) Spark added vs EGR. EGR is only active when coolant is above 120 degrees and over 3.5% TPS. So if your TPS is set wrong you could be activating the EGR system. Someone will ask doesnt EGR rely on MPH too, yes it does but in the BIN its set to 0 MPH.

3) The O2 Thresholds are set to make the O2 switch on the lean side of stoich. Not good for smell. This is changed in the Cali BIN. In the Non emissions BIN they are 50 mv higher. That may not sound like much but its the world when you talk about a sensor that uses less than 1 volt.

4) The open loop lean Limit and Max Lean are 2 points higher. Again, running the engine leaner for emissions.

Screen%20Shot%202015-08-19%20at%205.59.28%20PM-X2.png


So what to take away from this.

You have a Cali Emissions BCC. This will run lean with less timing. Lean and low timing stinks very bad, it makes for a HOT exhaust. That in turn warms the cat. Lean lowers HC and CO emissions but NOX goes up. NOX is that eye watering choke condition. BTW you are set to enter closed loop at 150 degrees.

On to the performance side. I will grab some more pics of a performance tune and post it up.
 
Last edited:
Otay, lets just hit the basics. Think back to a carb. You need correct fuel for air and correct timing.

Here is a very basic shot of cleaning up a stock tune that will run substantially better on a stock rig. I say basic because I have 5 tables open out of maybe 50 that get adjusted. Also, the timing table shown is a rough table and final by no means but its also not a hot table at all.

Screen%20Shot%202015-08-19%20at%206.40.50%20PM-XL.png



So you see that the timing doubled and even tripled in spots. This table with proper fuel does not ping a lick. Timing is all in by 3600 and in the proper range for a SBC. There is no timing being added by any other table.

You will also se PE, Power Enrichment. This is TPS vs AFR. This is setup for proper AFRs with fuel today. You also see that as RPM go up TPS goes down. This is to keep you in PE easier when in the higher RPM range. That way if you are in and out of the throttle slightly you do not get any type of surging.

Next to all that is AE, Acceleration Enrichment. Thats your old school pump shot. TPS is quick hit to help fatten up and MAP is the duration until the VE table can even out. These are very important when working on a total custom tune.... Why would be a whole other conversation.

Now you will see I didn't put up a fuel table. Thats because this theory is based on a stock engine with a stock tune. That should not have to be adjusted as long as the fuel system is healthy.

Remember this info above is very basic and is more operation than tuning advice. LOL
 
To eliminate some confusion. The shots are not Cali vs Non Cali. The top is Cali and the Bottom is the start of a custom tune.

Timing from Cali to Non Cali is described in the post with all the Cali data.
 
You must log in or register to reply here.

Latest Posts

Top Bottom