Interesting Tach Issue

[EmersonHart13]

Working through the short list of general maintenance and issues on the 99 Suburban with a 5.7.

When off the tach needle rests at the bottom just below 0, as it should.
Put the key in and turn to on but do not start it and it reads 1800 or so.
Start the truck and it reads somewhere around 2600.

Um, yeah, that ain't right!

Anyone every seen something like this before?

TIA,

John

Click to read more...

 

[Frank Dukes]

had a tach drop out ocasionally on an old car and it was the CPS. food for thought.

 

[EmersonHart13]

CPS, Crank Position Sensor?

 

[Frank Dukes]

indeed.

 

[EmersonHart13]

Did it throw an engine code?

 

[Dasfinc]

Working through the short list of general maintenance and issues on the 99 Suburban with a 5.7.

When off the tach needle rests at the bottom just below 0, as it should.
Put the key in and turn to on but do not start it and it reads 1800 or so.
Start the truck and it reads somewhere around 2600.

Um, yeah, that ain't right!

Anyone every seen something like this before?

TIA,

John

I've seen this with tampered gauge clusters before (common on riced-out hondas), for example, if you pull the needles off to install white faced gauges, and then re-install a needle incorrectly. It will still read 0 when off, but when turned on will jump to the wrong number. IF THAT IS THE CASE, and its just reading 2000RPM high, you can remove the dash cover, and remove the cluster. Remove the clear plastic 'shield' or cover, and then plug the cluster back in again. Start the truck, remove the needle, and reinstall it where it would be at warm idle. Turn off the truck, start it back up, see if it has been corrected.

this can also happen if someone swapped a cluster into the suburban that was out of a different model with a differen't V-8, or even a V-6 as the cluster may be interpreting the signal wrong as there are resisters etc. in the cluster. I've seen this frequently with Explorers/Rangers since the ranger platform came with 4/6 cylinders, while the Explorers came with 6/8's but shared the same cluster (Ala nearly all late 90's chevy trucks as well)

For example: My ranger was originally a 4 cylinder, and I put a V-8 into the truck. With a V-6 cluster, it read almost 'double' RPM's.

There may be a sticker or code on the back of the cluster that you can google once you pull it out of the truck.

 

[EmersonHart13]

I am thinking it is that because the motor was swapped and it runs fine. I actually had that problem when I put white face gauges on my old GP and had to place it again. I probably need a scan tool to see what the actual RPMs are first.

I just did some reading on the CPS and usually it results in a no start condition which I do not have problems with.

 

[Dasfinc]

I am thinking it is that because the motor was swapped and it runs fine. I actually had that problem when I put white face gauges on my old GP and had to place it again. I probably need a scan tool to see what the actual RPMs are first.

I just did some reading on the CPS and usually it results in a no start condition which I do not have problems with.

Could be a different year engine than the truck.

Explorers for example used a 3 wire CPS on the V-8 from 96-98, and then switched to a 2 wire CPS for 99-01.

 

[Bob Kazamakis]

What kinda basket case did you buy John?

 

[EmersonHart13]

I know for a fact it is different. Motor is a 97, truck is a 99. The sensor is the same part number.

THE BIG KIND! Not really a basket case? This is the only problem other than some basic crap like a tail light out and other normal maintenance.

 

[Bob Kazamakis]

What happened to the original engine? They're just sbc's in those right? No LS till later?

 

[EmersonHart13]

No LS... It is an L31... 5.7 Vortec V8. I believe it wore out. (I asked more questions about the new motor than the old one) Which is rather surprising considering these things have a 200k+ life expectancy.

 

[Dasfinc]

I know for a fact it is different. Motor is a 97, truck is a 99. The sensor is the same part number.

THE BIG KIND! Not really a basket case? This is the only problem other than some basic crap like a tail light out and other normal maintenance.

are you SURE the sensor is the same? Some systems are bad about which year some of these change-overs happen. Advanced had the same part number for all years of the V-8 explorer, but Rock Auto showed it had changed.

I'd do some digging to see if there are any other sensors or wiring differences between the 97 and 99's.

 

[EmersonHart13]

Well according to the research I have done they are the same, but yes there is always a chance. I checked a few different sites and no one has shown a difference yet.

The guy messed with the cluster to adjust the mileage to that of the new motor so I would not be shocked to find that he did not put the needle on right.

And on a side note I love Rock Auto prices!

 

[Bob Kazamakis]

Illegal. Sue him.

 

[EmersonHart13]

Car is over 10 years old, mileage doesn't matter. And I have the CarFax and it is still the nicest truck I saw at this price point.

BTW switch your avatar back, the old one was cooler.

 

[Bob Kazamakis]

!

 

[Bob Kazamakis]

But I got 2 soda pops

 

[EmersonHart13]

LOL, drunk at work again?

 

[Bob Kazamakis]

BETTER?

 

[EmersonHart13]

Yes, thank you.

 

[Runtz52]

i had a similar issue with my speedometer in my civic, would be at 0 turn the key to on and it would jump to 20 and stay there regardless of how fast u were going, trip and odometer stopped working as well, swapped in a new speedometer and its all good now,

 

[Dasfinc]

i had a similar issue with my speedometer in my civic, would be at 0 turn the key to on and it would jump to 20 and stay there regardless of how fast u were going, trip and odometer stopped working as well, swapped in a new speedometer and its all good now,

Civics especially are known for this (Because of those cheap white-faced gauge inserts).

 

[Runtz52]

Civics especially are known for this (Because of those cheap white-faced gauge inserts).

i had a full si gauge cluster in there, worked fine when i got it back in dec and around feb it just stopped working, might have been the vibrations from the innovative mounts, noew i got a blue speedometer from a civic ex and orange tach and gas/temp gauges lol

 

[EmersonHart13]

But they look SO good.