Sean Brereton

I have some trouble recently with my 305 tbi hesitating under acceleration? It appeared to only happen once the engine had warmed up after i had not driven the car for a few days. I read somewhere that the EGR or map sensor could be a fault? The car has thrown up a code 32 in the past which i believe is something to do with the EGR. Anyway i went to check the EGR and the two nuts that hold the valve on were loose. I took the valve off and the vlve appeared to hold under a vacuum and the plunger did move when forced so i assume the valve is ok. M

Sean Brereton

My question is would the valve nuts being loose have caused the problem? I dont know enough about the EGR system to know if it would cause this effect. I

TylerSteez

iTrader: (3)

valve nuts? are you referring to the rocker arms? what makes you think it would involve the valvetrain?

bop11

Fault 32 is EGR. Lose bolts would mean you have a nasty vacuum leak in the intake manifold. The EGR allow a small amount of exhaust gas into the intake. Because the exhaust is not combustible it cools the combustion chamber reducing nitrogen compound emissions. The opening of the EGR is controlled by the computer which pulses a solenoid in a vacuum line to the EGR valve. At idle, when cold or at WOT, the computer keeps the solenoid closed so there is no Exhaust Gas Recirculation. All other times the computer modulates the vacuum to the EGR via the solenoid, controlling the amount it is open. If the EGR is not sealed to the intake manifold, you have a vacuum leak that is after the MFS and therefore unknown to the computer. Not too bad when the engine is cold because the computer runs it rich. But at temperature or under WOT, the vacuum leak leans out the engine and it runs poorly.

Sean Brereton

Thanks guys. Hopefully that was the cause of the problem. The car has run ok for the last two days so i will see how it goes.

ASE doc

Did you replace the EGR gasket? It is probably damaged from the mounting nuts being loose.

eseibel67

This is all true except the EGR solenoid is not pulsed or modulated. The computer can either open or close the solenoid in order to apply vacuum to the valve. That's it, yes or no.


EGR systems designed shortly after these give the computer varying control of, and the ability to take feedback from the valve.

ASE doc

In fact, the valve is controlled by ported vacuum and exhaust pressure. The ECM only allows or disallows the ported vacuum to the valve.

bop11

From the mouth of GM
The EGR valve is opened by manifold vacuum regulated by an ECM controlled solenoid that uses "pulse width modulation". This means the ECM turns the solenoid "ON" and "OFF" many times a second and varies the amount of "ON" time("pulse width") to vary the amount of EGR.
The ECM uses information from the following sensors to regulate the EGR solenoid:
Coolant Temperature
Throttle Position (TPS)
P/N Switch

Pulse Width Modulation is quite common method for computer controlling of flow, pressure and temperature. In the gas business, we use it for Mass Flow Controllers and Electronic Pressure Controllers. Modern stoves and ovens use it to control the temperature in ovens and range tops.

ASE doc

This is correct, but, as I said, the vacuum source to the solenoid is ported, so that the valve is only opened when the ported vacuum signal is active, which is part throttle, cruise.

It's a sort of dual control. At cruise, when the ported vacuum signal is active, the ECM uses PWM, or duty cycle control of the solenoid to manage flow. At full throttle or idle, ported vacuum drops off and the valve closes. The vacuum EGR valves used on this model range are mostly negative pressure modulated and some are positive pressure modulated, which means that they are also controlled by exhaust pressure.

bop11

Totally agree with ASE. One thing to check is that the solenoid valve is connected to the EGR properly, that you don't have the hoses reversed. The solenoid when electrically disconnected has one hose which is open to air. You can suck through it to find out which one. The other hose will hold vacuum when sucked on. The open one goes to the EGR valve. This allows the vacuum in the EGR to escape when the solenoid is turned off by the ECM. If the solenoid has its hoses reversed, then you have an intake leak to air when the solenoid is off and once vacuum is applied to the EGR, it will stay open since the vacuum will never be released. Make sure that the hoses are correctly connected.

ASE doc

I'd like to offer a brief warning on sucking on any hose connected to an engine. I've gotten myself a little sick a few times sucking in gas fumes or exhaust. Better to use a vacuum pump to test things.

nortrek99

Sorry to "bump in" but I simply must! When I disconnect my EGR at the saucer side and put a plugin, my car will not hesitate, and the hesitation I fear will eventually ruin the car. When it is plugged in, it hesitates and I lose power...sometimes I hear "pinging" or "rattling" when it bucks or hesitates. The problem is, if I leave it disconnected, this is VERY HARD on the valves and CATS, and I do not want to do this just to drive the car w/o problems. At a stop sign, with it disconnected, I can also hear the rattling or pinging. I switched to premium to no avail. I replaced the EGR valve, solenoid, and position sensor on top of the EGR. No change. My only option left is to replace those plastic hoses that lead to the EGR and I have patched them in four places. Where the vacuum line attaches is a metal port under the plenum, and it is attached by a rubber elbow connector to accommodate the plastic hose. I cannot pull it off and if I blow throw the same hose on the solenoid side, it feels blocked. I suspect the rubber hose has melted over the port and must be chiseled off.
Any help I would appreciate.

Vader

Welcome Aboard!

If it helps with your diagnosis, there should be NO EGR function with the engine at idle. Disabling the EGR valve by removing the vacuum hoses and/or solenoid with the result being "At a stop sign, with it disconnected, I can also hear the rattling or pinging" should be no different from a properly functioning EGR, since the ECM would also have it disabled at idle and at acceleration from a stop sign.

It the hoses and tubes are suspect, they should be resolved before further diagnosis. Access is not as easy with a TPI, so it would be prudent to to route all new lines before installing the plenum. Keep in mind that it is not a violation of EPA rules to replace all of those hard nylon lines with custom bent tubing (copper works well) and allowing for a short piece of accessible rubber vacuum hose at the connection points.

nortrek99

This is what I have done so far: replaced plastic hoses leading to the solenoid with rubber vac hoses. This source of vacuum comes from a ported nipple under the plenum on my 88 Ford Thunderchicken with a 5.0 engine. Upon removing the EGR, I used a round brass brush and SUCCESSFULLY CLEARED all carbon ports coming in and out of the throttle body, and used a metal gasket that bolts to the throttle body.
My symptom is as follows, following a cold start, the car will run correctly for a good six blocks, then "lean out" or drop RPMs and the vehicle loses power and hesitates for about a minute. The computer corrects the issue and cleans up idle and the car is drivable. If I disconnect the hose from the EGR at the vacuum port diaphragm and car runs correctly and is a joy to drive again. However, nobody passes smog with a d/c EGR, I heard mixed opinions that you will destroy the engine by d/c EGR ( I don't see how this is possible because the cars ran great before the EGR valves came out). Very frustrated- would like some input and thanks to all of you for your understanding.