Running Rich, Making me Broke

[CBidzinski2010]

Hey all,

87 k20, 350sbc with sm465. Took her in to get inspected and aligned today since I finally got it on the road after waiting 5 months for my title. Shop owner and mechanic say the truck is running very rich which sounds right since I burnt half a tank of gas today. They said it could be an o2 sensor or apparently there are two coolant temp sensors they believe. I've already replaced the one temp sensor on the manifold and was wondering if anyone knows where the second would be. They said that the second one controls the computer and the temp gauge. And my temp gauge is currently not working.

Any input would be greatly appreciated.

Thanks Again,

Cody

 

[Georgeb]

The one on the manifold feeds the computer. The one on the left head between the 1 and 3 exhaust ports is for the guage. Check to see that the truck is warming up sufficiently should have a 195 deg thermostat in it. Next would be to go on a mission cleaning and checking grounds. Primaily that one in the front by the coolant sensor in the manifold by the thermostat housing. Mine ran really rich untill I spent some time timkering with it.

 

[bucket]

Sounds like the shop only knows how to throw sensors at a problem and hope it fixes something.

First things first, need to record the actual mileage and see what it's getting. Or is it running poorly and smoking noticeably?

 

[CBidzinski2010]

Does anyone have a part number for the sensor on the left head between cylinders 1 and three? It isn't the same as the one that goes into the intake manifold is it?

 

[bucket]

Does anyone have a part number for the sensor on the left head between cylinders 1 and three? It isn't the same as the one that goes into the intake manifold is it?

You can get it from any parts store, it is the gauge sender. With the wire unhooked, the gauge should be pegged. With the wire grounded, the needle should be at full cold. With the ignition on, of course. If your test doesn't get those results, it won't fix your gauge and there is another problem.

But that sender has zero effect on mpg or how the engine runs.

 

[CBidzinski2010]

Well I guess tomorrow I will clean up that ground on the intake manifold off of the coolant temp sensor and see where that gets me, the ses light came on and then went back off so I'm going to try to read that code as well, will the cpu store a code even if the light is not currently on? The cts is brand new bit of I unplug it the truck idle will raise up. Them it drops as soon as I plug it in. I guess I need to run that code. Maybe it's a map sensor who knows I guess.

 

[chengny]

I burnt half a tank of gas today.

If you're not familiar with SB's, one thing you'll quickly learn is that the gas gauge indication is wildly inaccurate. Like Mr. Bucket suggests:

First things first, need to record the actual mileage and see what it's getting.

After a fill up, the gauge will stay pegged over the "F" mark for a long time. You'll start thinking that you're suddenly getting hyper-mileage. Then about 40 miles after the fill up, things change drastically. All of a sudden the needle starts to drop - and it drops fast. You can almost see it move to the left as you drive. This free fall continues until the gauge shows about 5/8 full, then it moderates. From that point on down you can pretty much trust the gauge.

This phenomenon is especially disappointing after you've made a repair - and bragged to your friends about what wicked good mileage you are getting since then.

If you can get 11 -12 MPG out of a 1987 4WD 3/4 ton SB with a 350...consider yourself lucky.

I couldn't find the EPA mileage ratings for an 87 K25, but here is the spec sheet for an 86 K25 with a 350 (the 1987 V25 was identical):

You must be registered for see images attach

 

[Speakfordadead]

I burnt half a tank of gas today.

If you're not familiar with SB's, one thing you'll quickly learn is that the gas gauge indication is wildly inaccurate. Like Mr. Bucket suggests:

First things first, need to record the actual mileage and see what it's getting.

After a fill up, the gauge will stay pegged over the "F" mark for a long time. You'll start thinking that you're suddenly getting hyper-mileage. Then about 40 miles after the fill up, things change drastically. All of a sudden the needle starts to drop - and it drops fast. You can almost see it move to the left as you drive. This free fall continues until the gauge shows about 5/8 full, then it moderates. From that point on down you can pretty much trust the gauge.

This phenomenon is especially disappointing after you've made a repair - and bragged to your friends about what wicked good mileage you are getting since then.

If you can get 11 -12 MPG out of a 1987 4WD 3/4 ton SB with a 350...consider yourself lucky.

I couldn't find the EPA mileage ratings for an 87 K25, but here is the spec sheet for an 86 K25 with a 350 (the 1987 V25 was identical):

You must be registered for see images attach

Cricket... My 8.1 gets better than that!!!

 

[yevgenievich]

Cricket... My 8.1 gets better than that!!!

They generally will get better mpg than older small block trucks with no OD. OD and mpfi help.
My 91 V2500 suburban could manage 14-15mpg highway before i changed tires and started driving 75-80mph. While in cali with their generally lower speed limits and stock tires it did very well. Now it is pretty much 12-13 and around 11 of more mixed driving. Still not as good as the 97 big block c3500 crew cab I used to have(15-17 at 75-80mph).

 

[CBidzinski2010]

Alright, so it flashed code 13 and code 15 to me, I looked them up and 13 is the oxygen sensor, and 15 is the cts. I have replaced my cts though so I'll have to clean the ground on it and see if that helps. The truck bogs when at low rpm and runs like a top at the higher end. This is where the rich running idea is coming from, not just due to fuel usage, maybe I should have been more clear about that sorry.

 

[yevgenievich]

That would indicate running rich condition. After checking cts, other things to look at are ignition and fuel pressure

 

[Speakfordadead]

They generally will get better mpg than older small block trucks with no OD. OD and mpfi help.
My 91 V2500 suburban could manage 14-15mpg highway before i changed tires and started driving 75-80mph. While in cali with their generally lower speed limits and stock tires it did very well. Now it is pretty much 12-13 and around 11 of more mixed driving. Still not as good as the 97 big block c3500 crew cab I used to have(15-17 at 75-80mph).

Agreed.... I get about 17 when long hauling from Bay Area to SW WA.... and when I romp on it.... it makes me smile....

 

[bucket]

Alright, so it flashed code 13 and code 15 to me, I looked them up and 13 is the oxygen sensor, and 15 is the cts. I have replaced my cts though so I'll have to clean the ground on it and see if that helps. The truck bogs when at low rpm and runs like a top at the higher end. This is where the rich running idea is coming from, not just due to fuel usage, maybe I should have been more clear about that sorry.

You probably got the code 15 when you unplugged the CTS with the truck running.

If the O2 is plugged in and the wiring looks good to it, it would be a good idea to replace the sensor. It also would be a good idea to check the timing after that. Timing set back too far can cause a lack of low end power and poor mpg.

 

[Georgeb]

You probably got the code 15 when you unplugged the CTS with the truck running.

If the O2 is plugged in and the wiring looks good to it, it would be a good idea to replace the sensor. It also would be a good idea to check the timing after that. Timing set back too far can cause a lack of low end power and poor mpg.

Yeah, I believe the factory spec is 0 deg but mine liked 10 deg advaced

 

[bucket]

Yeah, I believe the factory spec is 0 deg but mine liked 10 deg advaced

That's my experience too. 8-12 advanced works best in most cases.