My car is idling kind of rough and sputters under load. I was thinking a vacuum leak and was checking things like the fuel pressure regulator. When i disconnected the vacuum line to the regulator nothing changed. Should the idle quality have gotten even worse?

------------------
1989 Iroc-Z TPI 350 auto 4-spd Removed MAF screens K & N filters, Hedman smog shorties, accel 8mm wires, made for you wire looms.

 

Anyone?

 

When you disconnect the vacuum line from the FPR, it should simulate FP at WOT...I'd expect the fuel pressure to increase 5-6 PSI anyway, and at that time, the idle quality should change some.

Is there vacuum on the line when you pull it off?

 

There is vacuum when i disconnect the line, i tried to see if there was any fuel being drawn up by the vacuum but i couldn't se any. It idles rough, runs rough under load at low rpm's but smooths out above idle when in gear and in park/neutral.

 

If you're suspecting a fuel problem, best thing to do is purchase fuel pressure gauge. Also a vacuum gauge to see what's happening.

Does it set any codes?

Have you tuned it lately?

 

No codes, runs closed loop, fresh cap rotor and plug wires, fresh o2 sensor installed with headers. Ran fine for about a month but now somthing jacked. It's like one day i started it up to drive home and when i got home the car was ideling rough and the next day it was running crappy like i said before. It acts like a vacuum leak or a fuel problem but all the intake gaskets were replaced with the motor six months ago. The cars got a lot of hard miles on it so i'm still working bugs out of it.

 

Do you do a lot of idling and stop and go? Could be an issue with headers cooling down and the car running in open loop..and a little too rich, causing the O2 sensor to foul or get lazy.

A heated O2 sensor may be in order.

Seems as if you access to a scan tool, monitor open/closed loop and O2 sensor when putting around.

Also, look over the plug wires real good, may have burnt one on the header.

Thing is, unless it's a pretty significant vacuum leak, a TPI car can adjust to some degree, in fact the IAC valve really is a controlled vacuum leak to maintain idle.

A compression check should put your mind at ease (or realize your fears) if it's internal.

Back to your vacuum line and FPR test...this may be as simple as a clogged/clogging fuel filter, or a weak fuel pump, you can eliminate the filter quickly enough by replacing it, but will stil need a pressure gauge to check out the pump.

You can also get "old school" as well, disconnect a plug wire at a time and see if the idle chages....do the same with the injector harness connectors too.

 

I already have a three wire o2 sensor, and an autometer a/f gauge, the car is running closed loop almost all the time. I pulled the plug wires off one by one and all i learned from that was that i could shock the crap out of myself . When i disconected the plugs i noticed a difference with all of them, i'm gonna pull all the plugs and wires this weekend i guess. I didn't think to try it with the injectors I'll do that when i get home today. Could i have a bad injector?

 

Aw man, I had to laugh.

Hmmn, if you get a idle decrease when pulling the plugs, you're most likely getting fuel into the cylinders as well.

You could still have a fualty injector with a weak spray pattern, but the only way to know would be to do an injector bleed down test on each one with the proper tester (about 60-70 bucks) or send them out for cleaning.

Another thought is the MAF sensor, you can disconnect the harness at the sensor and see how it runs, the MAF has direct input to timing and fuel control.

Is the TPS working correctly, set to .54v at idle and a smooth sweep through to WOT?

Problem with all the guessing as to what it could be, is you can toss a lot of parts at it, and get nowhere.

You need to narrow it down to fuel, ignition, internal engine (bad valve, broken valve spring,etc.) or a bad sensor. The easiest way to do this is with the proper test equipment, which in the long run will be cheaper than a few hours of shop time, besides having some new tools in the shop to show off to your buddies

 

I haven't tested the tps, but that's very possible it has had a slight bog off idle when the throttle is snapped quickly. Looks like i got a few things to test this weekend. I pulled the maf and that didn't change anything. I'm gonna go today and buy a fuel pressure gauge.

 

Problem solved, i had a burnt plug wire. It was the number six so it was pretty hard to see. Runs alot better now that it's hittin all eight.