1995 Isuzu Rodeo Question 2-3k RPM hesitation/sputter

KENYU73

MEMBER
1995 ISUZU RODEO
6 CYL
2WD
AUTOMATIC
155,000 MILES

I've been racking my head over this. I've replaced the O2, Fuel Pressure Regulator and IAC value. I've also swapped out the TPS and MAP sensors (then returned them as they didnt help). I'm currently putting new exhaust on from the manifold back (new cat and muffler inc). I've also replace most vacuum lines. The coils appear fine. Fuel pressure reads 33-36psi

If the new exhaust/cat doesn't fix it. What else could it be? Once I get over 3k RPM the engine is smooth and accellerates fine.

I would like to have some good ideas of what to check for next.

Thanks!

3 Replies

KHLOW2008

MECHANIC
41,815 POSTS

Hi kenyu73,

Thank you for the donation.

Since the power is not affected after 3000 rpm, it should not be due to a clogged catalytic coonverter.

Symptoms seems to indicate an EGR fault as the more likely cause.

Try disconnecting the EGR vacumn hose and plugging it to test if problem goes away.

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Friday, July 10th, 2009 AT 11:33 AM

KENYU73

MEMBER
4 POSTS

I removed the EGR value and the diaphram lifts and sets as I applied vacuum at the hose. I didnt notice any hangs or binding.

I had to order a new gasket before putting it back on, but there is also a electric relay and another diaphram looking piece before the EGR itself.

Vacuum line-->electirc relay switch-->small diaphram--->EGR

I do notice that when I apply throttle, the electic relay clicks. I assume this enables the vacuum past idle.

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Thursday, July 16th, 2009 AT 9:11 AM

KHLOW2008

MECHANIC
41,815 POSTS

Yes, when throttle is opened, the solenoid would click to allow vacumn to work the EGR valve. The diaphragm that you mentioned is the back pressure transducer. It prevents the EGR valve from closing abruptly when the solenoid stops working.

Here are testing ptocedures for the EGR.

1. Check vacuum lines for correct routing. Disconnect vacuum hose at EGR valve, and plug hose end. Connect vacuum pump to EGR valve. Start engine. Apply 4.7 in. Hg to valve and hold.

2. Engine speed should drop at least 100 RPM or engine should stall. Vacuum should not drop more than one in. Hg in 30 seconds. Reconnect EGR vacuum hose. With engine warm, increase engine speed. Ensure EGR valve stem moves up.

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Thursday, July 16th, 2009 AT 1:42 PM