Alpine951

OK, I will try to start from the beginning. I posted a bunch of times last year related to my problem. Last year I put in a new Vitesse MAF. The car ran terrific. Drove it for two months since the initial install with a wide grin always on my face. All the driving was always at part throttle. Never went WOT. Then one night on the highway cruising at 80mph in 4th or 5th gear I decided to bury the gas pedal to WOT. The next day the car would not idle well and was idling lean, 17+ afr. John Vitesse thought everything pointed to a vacuum/intake leak. Made sense. I did all kinds of leak testing but never found any massive leak. One of the things I did was clean all the grounds except for the 2 under the dash, and I replaced the Battery ground cable with a new one. Still no change. At various times I did notice that if I stepped on the brake the idle got good. That is why I started cleaning grounds. Car never was right last year when I put it away in the garage for winter. When I pulled it out this year it was same but also would have a rising idle up to 1600 rpm and then drop down, then rise again and drop. Been told that is because the ECU knows to shut off the injectors with the throttle closed if idle gets to 1600. Brought the car to a Pcar specialist that is local and they started with a smoke test and found nothing leaking enough to cause this. They think it is a ground problem. They have the same Vitesse system on their race car and are experiencing similar issues. They said the system is very sensitive to ground issues. They think my problem is a ground issue and think all the grounds need to be gone through and tested/cleaned. I told them I cleaned them last year. I didn't test them though. Its going to cost a big chunk of change to go through grounds at $125/hour so I am thinking I need to tackle this myself. Can anyone explain to me how and where I would test the grounds? really want to get this car back to right again. At the time the maf was grounded to a screw on the headlight frame. Then I went to the ground point near the headlight and now I spliced a wire and ran it to the battery.

Alpine951

will do some googling on how to approach this. Have a multi meter just not used to using it so have to reeducate my self.

rlm328

I test for continuity between what ever is being ground and ground. If I have continuity I check the voltage drop.

Tom M'Guinn

I think you need to find a different shop in all honesty. The Vitesse MAF is a red herring. Bad grounds can cause all sorts of problems for sure, but to suspect bad grounds just because you have a VR MAF makes me doubt your shop. Also, grounds generally don't go bad all at once as a result of going WOT. And, the idle can't go up to 1600rpms without extra air. Extra air comes from vacuum leaks or ISV issues (though the ISV can go haywire due to bad electronics). If stepping on the brake pedal alters your idle, then you also might want to look at your power brake booster, as it may be leaking internally. Don't mean to sound critical (I'm not) it just sounds like you need more and better help than you are getting. There's nothing wrong with checking grounds, of course, and stranger things have happened, but it sounds to me like you could use help from someone who has the skills/knowledge to systematically diagnose the issue.

But to answer your question most people start by physically inspecting the ground points, with special focus on the bell housing ground. Take them off, and clean up the contact points with emery cloth. That will fix the majority of ground problems honestly. You can then find any other issues (lurking in harnesses and crimps, etc.) doing exactly what rlm328 says above.

PaulD_944S2

Another source of problem for the grounds is the crimp of the wire inside the lug or connector that is attached to the engine or chassis ground.

Sometimes wiggling, twisting, or lightly pulling on the wire into the lug may reveal a weak or corroded crimp.

jmj951

You can help isolate the VR MAF by running a ground directly from the MAF to the battery post (I was advised to do this by John V to isolate potential ground problems when diagnosing a different problem).

I take it you don't have any of the Vitesse diagnostic capabilities, such as the MoMonitor? If you did, that could be an enormous time saver.

fast951

The issues you are experiencing are not symptoms of the classical ground issues.
Of course, it's always a good idea to inspect and repair grounds, but there is something else going on here.

For starters, as Jon suggested and for your peace of mind, isolate the MAF ground by connecting it directly to the battery NEG (-) pole.

As Tom also suggested, the sudden change after a boosted WOT and the higher idle lead me to think there is a vacuum leak.

Smoke testing the intake system reveals many possible leaks. However, unless you perform a "pressure" test, you are not going to find every leak. Some require pressure/heavy vacuum to show.

Have you inspected the BOV, most shops do not include it as part of the vacuum/smoke test.
Have you visually inspected the MAF?

Look outside the box. I had a customer reporting a problem, it ended up being the BOV hose provided with the kit. He left it inside the air filte (by mistake)r, and it was obstructing the air flow once it jammed against the MAF sensor. Look at the simple things..

I'm convinced your problem is not ground related. Usually, a bad MAF ground causes rich idle not lean as you reported. Ground problems to not happen suddenly, your problem showed up after a WOT/Boosted run.
An air leak causes a lean idle and a very rich condition under boost. A vacuum/pressure leak does occur suddenly after/during a boosted run. High idle means air is getting into the engine.
Your car is experiencing all of the above. All leads us to a common cause: vacuum/pressure leak.

Dave951

This is a real wildcard but are you using silicone hose for your vacuum routing? If so what ID/OD thickness hose did you use? It has been reported that some thin wall silicone hose for boost/vacuum applications will collapse under vacuum and cause a ton of different headaches.

Willard Bridgham 3

If you are going to inspect crimp connectors, solder them before you are done.

Mechanical electrical connectors fail frequently and way more frequently with age/heat cycles.

Alpine951

I disconnected the vacuum line at the booster and plugged the line. no change. I would expect the idle to improve when I plugged the line if in fact the booster was leaking internaly

Alpine951

Hey John, I think that I do have it grounded directly to the battery post as I initially had it elsewhere but then went to the battery last year based on your suggestion then. I did a bunch of pressure tests last year spraying soapy water everywhere. Guess I will have to try again.

Tom M'Guinn

What is your vacuum at idle?

Alpine951

Just got the car back. The up and down idle is gone for the moment. I can't ever recall noticing what my vacuum has been all this time since the problem started ( how could I be so stupid!!!) but right now it is 9. That is low!! I know it used to be higher. I was just searching on here because I know I responded to a poll on vacuum a long time ago but can't find it. I know it was higher though. Low vacuum also points a leak I guess.

Tom M'Guinn

Right, 9" is low. You want to test after the car is fully warmed up, and account for your elevation and rpm, but 9" is about half of what you want generally at sea level at factory idle speeds. With any luck, the low vacuum is the result of a leak and you just need to find it. However, it is also possible you broke a piston ring, burned a valve, or had some other internal failure that night when you floored it. I would start with a simple compression test (or leak down if available) to make sure the motor is still sealing up inside. Assuming it's ok inside, then all signs point to an external leak somewhere that you just need to hunt down.

Alpine951

Now it's at 11 , 900 rpm warmed up.