Tach reading low? (New sensor)

[jrad235]

Hey guys,

I bought a new OE sensor and installed it the other day. The tach reads 400RPM at idle. Sounds fine, and I can take off fine(Stick shift). Also, when towing(55mph), When I spin it up, I can't seem to get the needle to go past 2400 RPM, and I don't want to downshift to third to see what will happen. It will free-rev to 3200 on the gauge, but it seems all-in-and-done at 2400 while towing.

Do I just need to quit being a candy-ass and push it? FYI, 12k Lbs of truck/trailer does NOT like 1500' of elevation. I'm pretty much crawling at that point(30mph)

She is making noise for sure at 2400, and I don't have another truck handy to check out. (Breaker-breaker, Plywood, come on)

 

[OLDBULL8]

It seems to me that if the tach reads 3400 just setting and you rev the engine to 3400 that is top revs for the 7.3 then you run out of fuel and power. Since you have an N/A engine, at 2400 RPM you have run out of power, to achieve any more power you would have to add a turbo and turn up the IP fuel. To gain a little more HP, you will have to shift down to a lower gear, that would let the engine turn at a higher RPM. The higher you go in elevation, that in effect reduces the HP, you could try adjusting the IP for more fuel by turning it up by one hex.
Are you blowing any black smoke at the 2400 RPM?

 

[jrad235]

Yes, she blows black smoke, she just won't go. Timing maybe? I'm having trouble advancing it slowly, and I hate hearing lots of clatter when it's cold, makes me think she's going to come apart.

Edit: I should say, she putters a good dark fog. I don't want to melt a piston, so I usually lift out of the throttle till the smoke clears.

 

[TWeatherford]

At 1500 feet with 12000 lbs gross you should be able to get the rpms right to the governor, and do it in any gear on flat ground. 1500 feet above sea level isn't much. They really feel gutless at 9,000 plus.

 

[jaluhn83]

It's pretty common for the stock tach to read a bit low at idle and then correct at higher rpm.

Sounds to me like the trans isn't downshifting when it should.

 

[OLDBULL8]

It's pretty common for the stock tach to read a bit low at idle and then correct at higher rpm.

Sounds to me like the trans isn't downshifting when it should.

Personally, I've never known a manual tranny to downshift on it's own. Grab that handshaker by the ball on the stick and jerk it back from 5th to 4th or whatever.

 

[jrad235]

Personally, I've never known a manual tranny to downshift on it's own. Grab that handshaker by the ball on the stick and jerk it back from 5th to 4th or whatever.

ROFL! Good one. Sounds like no one has a definitive answer, unfortunately. It just won't hold RPM's while climbing. Just how much smoke is normal to get it to hold rpm?

 

[riotwarrior]

ROFL! Good one. Sounds like no one has a definitive answer, unfortunately. It just won't hold RPM's while climbing. Just how much smoke is normal to get it to hold rpm?

Check fuel pressure at filter head on load and see what's going on...small diagnostic things like this can help a long the path to correction.

 

[jrad235]

Damn, gotta buy more tools. I replaced the lift pump last summer when i was having starting trouble though. runs hard anytime it isn't towing...up a hill.

 

[iverger]

I pulled out of the quarry last week at 20,380lbs and ran up and down the hills between 700 and 1400' elevation on the way home. Was doing 55-60 in 4th with 3:55 gears at about 2400 rpm and didn't slow down much if at all for any of the hills. Not really any smoke at WOT at that rpm up the longest ones. I have a turbo but was 8k heavier. Everything is pretty well stock on mine as well.

Even with an N/A I don't think you should see much if any smoke after 2k.

 

[jrad235]

Well that is just frustrating. It must be my timing then. The truck feels fine around town, but It hates elevation. Pulls on the flat highway no problem. Hit the mountain...Bam. like a wall.

 

[Knuckledragger]

Perhaps timing, but could also be a stock N/A engine. They only made about 170 HP and around 300 lbs/ft of torque. That is being taxed by your load. 1500 feet of elevation is not much, but if it happens in 3/4 mile, it is a big strain. I towed light cars up a steep hill and could maintain 40 mph in second gear (C6) for two or three miles. Coolant temp got high but stopped climbing after 1/2 mile. Do you heat up or just lose power?

 

[jrad235]

That's a good question. I'm still waiting on my real gauges to arrive, so I've been playing it safe. I forget that other places don't necessarily have hills like ours. You are right, the last 600' is within .5-.75 of a mile. Does anyone by chance know which cylinder gets HOT first, assuming injectors are balanced? I'll probably tweak the timing a bit since it is warming up and give it a whirl.

 

[dmaxjoe]

Do you have a pyrometer? Testing on a hill, with a load, without one, can be bad.

 

[jrad235]

It is on the way. where is the best place to put in in the manifolds?