Low Boost

[CedarGrove]

My 98 K3500 is only putting out 3lbs of boost max. I would generally see 9 or 10 pulling a hill unloaded.

I noticed the other week that the vac pump seemed to be slightly noisier than normal. Do these vac pumps fade out like that or do they normally go all at once?

I just noticed the boost tonight so I have not done any poking around yet. I was going to look for leaks (exhaust and vac). Just wanted some insight on the vac pump.

Thanks,

Lewis

[Robyn]

HI

Check the vacuum at the pump, should be 26" and steady on a gauge.
If gauge wiggles, pump is shot.

Be sure the plastic lines to the wastegate actuator are in good order.

Also check the wastegate solenoid.

Generally the OBD II trucks will show codes if there are isues with low boost or ???

If the pump is noisy then its likely the culprit.

A great fix is to replace the vacuum system with a Turbo master
On a 98 truck you would probably want to step up and get a reprogramed ECM. The earlier trucks had a replaceable Prom.

The TM is a rod and spring thing that replaces all the vacuum stuff and is adjustable with a set of nuts on a the rod.

You also need to add a set of gauges so you can monitor the engine.

(Boost and Pyrometer)

Now the computer keeps things in check, with a TM you must do it to keep from melting your little 6-1/2


Let us know if we can help further


Missy

[CedarGrove]

I slapped a Turbo Master on it a few days after my original post and have not looked back since. The TM seems a bit spendy for the little bit of hardware that it is, but it seems cheap compared to the complicated vac system from the factory. It does the job more reliably for my K3500. EGTs are down. Boost, power under load, and MPGs are up. She'll climb a steep grade at 65 mph without breathing hard with the TM. Might get a SES light now and then, but no biggie.

The vac pump was what went tits up on my system. My little diaphragm dingy still seemed to hold pressure so if anyone needs one for a 98, let me know. We can make a deal. Deleted the vac pump and picked up a serp belt for a '93 which turned out to be a bit long at 101". Went back for a 99.5" belt and it's all good. If anyone needs a serp belt for a '93, give a shout. Also have the original belt for the '98 with the vac pump that someone might like to have for a spare. I'm not going back.

Lewis