Why is my Suburban "surging" at cruising speeds?

5DESERTRATS

MEMBER
1987 CHEVROLET SUBURBAN
48,000 MILES

Fairly new to me 1987 suburban with a 7.4 and 3 speed auto. Odomometer shows 48,000 (i honestly don't think it has rolled over).

mods made : throttle body spacer, jet perf. Chip (stage 1), and cat. Converter removal

recent repairs/attempted fixes: new fuel filter, new tranny filter and fluid, new cap, rotor, plugs and wires, tried a new egr valve(no difference), new egr solenoid, new O2 sensor

have checked for vaccum and intake leaks, none found

have bought but have not yet tried a new fuel pressure regulator. Have not checked actual fuel pressure.

hard accelleration seems to be fine.

i might notice a slight "miss" at idle?

any ideas?

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,709 POSTS

The first thing I recommend checking is the fuel pump pressure. Please understand I have to say this. It is federal law that the catalytic converter is in place. With that said, you have to keep in mind that the removal of the cat can cause issues with driveability. The O2 sensor sends information the the computer identifying exhaust emissions. If they are out of control (no converter) the computer tries to compensate for the difference by adjusting fuel mixturers. Chances are that is at least part of the problem. Start with fuel pressure and also check the fuel pump regulator to make sure everything in within spec. It sounds like you have worked around cars, but if you need directions, go to our homepage. Under the DIY section there are directions and a video explaining how to do it.

Let me know what you find and if you have further questions.

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Saturday, October 1st, 2011 AT 10:56 PM

5DESERTRATS

MEMBER
2 POSTS

Ya, I understand the disclaimer. Seems odd that fuel pump pressure might be an issue if it pulls hard under heavy acceleration. I suspected that perhaps the removal of the cat could cause my issues. I wonder if I add a more "free flowing" cat, I would solve my problem?

I'll have to check it out but does the "diy section" describe how to monitor fuel pressure while driving

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Saturday, October 1st, 2011 AT 11:06 PM

JACOBANDNICKOLAS

MECHANIC
109,709 POSTS

Actually, the pump may not be the issue. It could be the regulator. And yes, a free flow cat might be helpful. As far as the DIY, it explaines what should happen when the throttle is hit. Basically, you will see a sudden drop in pressure that regulates back out. If you check it when driving, it should still maintain the manufacturer's spec. I'm seeing between 9 and 13 psi on the TBI models.

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Saturday, October 1st, 2011 AT 11:15 PM