88 K5 hesitation question

[jamezz]

88k5 TBI 350 700R4. I'm getting a hesitation from a dead stop in drive and in reverse only. I rebuilt the throttle body yesterday due to injector problems and that took care of most of my issues. Now I'm just getting a hesitation when taking off and drive or reverse only, and when in park the idol when warm will fluctuate up and down . Is it safe to say it's probably a fuel pump? I haven't checked a fuel pressure yet. I was trying to see if somebody might have had any other suggestions before I dig into this.

 

[jamezz]

I also replace the EGR because it needed it desperately as well as the PCV.

 

[Wes Harden]

Welcome @jamezz

I would 1st check for vacuum leaks. Also after repairing the tbi, the computer needs to adjust it's fuel strategy. This can take some time. A few test drives from cold to fully warm may improve performance

 

[Blue85]

Describe this. New throttle shaft bushings? Did you clean the IAC passages? Did you put new gaskets on and what was your torque wrench set to? Was the battery disconnected?

I rebuilt the throttle body yesterday

If you don't find any vacuum leaks, check the IAC and look at the EGR. How does it drive at higher loads?

 

[jamezz]

No shaft bushings. Proper torque specs to the intake did not replace IAC all new gaskets new injectors AC Delco clean the throttle body and yes the batteries disconnected. Going to pull the IAC and give that a once over and go from there. It has a new EGR.

 

[Wes Harden]

As a test unplug and block the EGR vac line. Also there is vent filter in the EGR control solenoid, under round cap. I f this filter is super dirty it can stop EGR apply vacuum from venting

 

[jamezz]

As a test unplug and block the EGR vac line. Also there is vent filter in the EGR control solenoid, under round cap. I f this filter is super dirty it can stop EGR apply vacuum from venting

I just pulled off the IAC and it looks fine. I plugged it in outside the TBI turn the key on to see if it moved and it looks like it's working fine. I sprayed out the throttle body cleaner and put everything back together. It's got a new EGR valve but when I pull the back line off the EGR I get no RPM difference and when I plug it I don't get any thing different as well. What am I supposed to be looking for when plugging the back line off the EGR?

 

[Wes Harden]

The egr shouldn't operate at idle only at cruise while you are driving the truck. Aftermarket egr valves are notorious for being improperly calibrated. It could be opening at a much lower vacuum, or just be to large of an orifice, and interfering with your air fuel ratio as you accelerate. Unfortunately OEM egr are not available, even AC Delco are not accurate better but still spec'd for an average of applications. Unplug and drive the truck to see if there is any improvement.

 

[jamezz]

As a test unplug and block the EGR vac line. Also there is vent filter in the EGR control solenoid, under round cap. I f this filter is super dirty it can stop EGR apply vacuum from venting

I pulled the EGR control solenoid. Could you elaborate a little further on how to check the vent filter?

 

[Wes Harden]

There should be a round cap on 1 end, this cap snaps off and a round foam filter is fitted over a plastic nipple on solenoid, this the EGR vent and must be clear to allow vacuum release of the EGR control. Iirc when the design changed, but later EGR solenoid did not have the filter and many replacement parts do not. So if yours does not have this not to worry, simple test can confirm function. With power applied to solenoid it should hold a vacuum, no power, it should release.

 

[jamezz]

As a test unplug and block the EGR vac line. Also there is vent filter in the EGR control solenoid, under round cap. I f this filter is super dirty it can stop EGR apply vacuum from venting

Thank you for the heads up. I was sold an EGR for a manual and that's where my hesitation was coming from. I also had bad fuel pump and tank needed replaced. New tank, fuel pump and AC Delco EGR valve and she runs like a champ!