OK, my car run rich at idle some times, it isn't as bad as it used to be but something still isn't quite right.

The problem started 5 years ago, when I added Larger injectors, TPIS Big Mouth Intake & Large Tube Runners, ported plenum and 52mm throttle body. I have since removed the injectors and replace a lot of parts/sensors, thinking that was the problem.

Currently, my car has about 17" of vacuum at idle, it seems as though I should have 20"+ at idle. I pulled and plugged all the vacuum ports (TB, PCV, 2 in the rear of the plenum, & Charcoal Carnister, brake booster) to make sure I don't have a vacuum leak. I even tried two vacuum gauges, to make sure of my reading and I double checked every line. I tried carb clean around all the injectors, cold start injector and the top of the intake manifold, nothing seems to affect the idle.

Getting back to my TPIS Intake, it didn't quite fit straight on my heads, the rear seal on the block is about twice that of the front. (The first time it leaked quite a bit of oil everytime I got on the gas, so I had to really goop up the rear seal)

Does it sound reasonable that maybe my intake base is leaking? Perhaps sucking air internally from the engine?

I think my next course of action is R&R the intake and decide wether have in machined straight or get another intake.

Does anyone have any better idea to check for first. I don't want to do an intake just for the hell of it.


[Modified by dgoodhue, 5:44 PM 3/31/2003]

 

I'm not an expert here, but here are my thoughts.
If you did not have the chip done for this set up, the larger injectors would cause the rich condition at idle. As the car "learns" the new combination, it will compensate and therefore be "better than it was."
As far as plugging up all the vac points and the idle not changeing, the IAC would compensate for any differences.
Now the vac thing I'm not sure about... I'm thinking the larger throttle body may be able to lower the vac? If you made a smaller hole for the motor to breathe through, the vac would go up, so maybe vice-versa?
Also, if you installed a performance cam, they generally lower manifold vac.

 

I had a TPIS stage 4 chip burned for my application or atleast I thought it was. I now have all the PROM burning stuff/scan tools. My chip now is a stock 89 code with the injector constant and FP set for Ford Motorsport 24lb injectors (I think it is actually at 25.5 or 26.5) The only good thing about this problem has been, I have read all I can about my ECM and functionality so I have become pretty good at understanding that side of everything. As for better than it was, my MAF sensor was shorting out and I had wired my O2 sensor improperly, I had the trigger and power mixed on the relay.

I mentioned about the idle not changing because of the carb cleaner that I sprayed around everything. Suposedly, if you spray carb cleaner around a vacuum leak the idle will go up.

I have a stock cam and rocker rollers. I don't think the TB would affect my vacuum when closed at idle, but I could be wrong. I appreciate the question and leads as I know that not everyone know my vette's setup, situation and problems.


[Modified by dgoodhue, 5:42 PM 3/31/2003]

 

If the intake base is leaking as you described it should be at the rear ports; in that case the rear spark plugs should show a leaner condition while the fronts show richer burn.

Go to my site and use the method there to see if your ECM is going closed loop and staying there. It will also reveal if the ECM sees a rich condition as shown by O2 sensor readings.

BTW, my vacuum gauge indicates "normal" vacuum to be 18-22 in/Hg.

 

Another remote possibility is a plugged up catalytic converter. You said the car runs rich at idle, which can plug the cat. I also have low vacuum and have ruled out everything I can think of trying. I'm gutting the cat tomorrow after work, and then I'll check my vacuum. I'll let you know if it helped any.

 

That is a great idea, I never thought about that. I will check my plugs tommorow. I may have to take some pics of my plugs for you guy to 'read'

I definately hitting and staying in closed loop but only with a heat O2. My BLM act funny, they slowly move between 108 and 128. It cycle almost approx 3-5 minutes back and forth, which I think is odd. I put in a new ECM.

I wonder if some of my cylinders are running rich and lean and the ECM is try to compensate for each extreme causing it to cycle? Perhaps or maybe I am just pulling this out my rear because I really don't know...

 

I already plugged one Random Tech cat, but I replaced it. My New RT cat only has ~6.5 miles on it and idling (or approx 3/4 tank of gas) so I hope that isn't plugged yet.

 

I pulled the driver side plugs today, the front 2 plugs did smell a little richer than the rear 2 plugs, but otherwise they all look about the same black slightly wet. I maybe applying what I think is wrong to minor difference between the plugs though. I have bosch platnium +4 so they aren't exactly as I would see in plug reading pictures. The vertical edges of the plugs by the electrode have a tan color to them.

The problem with reading my plugs is that my car car has pretty much has only idled on them and for a little while my heated o2 sensor wasn't wired up properly, so I was running in open loop while idling.


[Modified by dgoodhue, 4:58 PM 4/2/2003]

 

I think the EGR valve could cause a lower vac reading

 

Use starting fluid rather than carb cleaner to check for leaks. I have not found that carb cleaner will not change the idle when sprayed on a vacuum leak.

The amount of vacuum you mention does not seem that low to me. Is your o2 sensor working correctly now? Also check the brake vacuum booster for leaks.

 

I will go out and buy some starter fluid tommorrow.

The o2 now works properly. The brake vacuum booster is relatively new, with somewhere around 3000 miles on it.

 

My EGR valve is almost brand new with almost 6.5 miles on it. I pulled the and plugged the EGR port of the TB and it didn't make a difference.