2g maf w/ 750cc injectors causing idle surge?

[forcefed86]

So after spending a couple more hours with the car today I'm stumped.

Car idled and ran great before I installed 750cc injectors and a 2g maf. No other changes.

Car now runs, No CEL. (14.5afr's at idle) Car now has an idle surge. Is this normal when still running factory ECU/eprom? I'm waiting on my chip at the moment. Just thought I'd get a head start on it.

I've checked all my vac lines several times, everything is as it should be. All the lines on the turbo intake pipe and top throttle body are capped.

The barb on the intake manifold closest to the TB is routed down to a "T" one going to the BOV, the other going to the MBC. The other barb on the intake closest to the FPR also has a "T" one side going to the boost gauge, the other to the AFPR.

The barb on the turbo outlet charge pipe is going to the alcohol injection boost switch.

Are there any other lines I could be missing?

I've checked the TPS and IAC etc. All pass resistance and voltage checks.

Any ideas?

Thanks

 

[habitatguy187]

, I told you not to install those until you got your tuning stuff.

 

[forcefed86]

Yea I know, I'm not cruisin' around or anything. Just want to have it ready so when my chip gets here all I have to do is drop it in and go. Figure if I have other problems it would be good to get them fixed while I'm waiting.

 

[hhuricane]

The computer has no way of controlling that large of an injector. You need something to tune them.

 

[forcefed86]

The computer has no way of controlling that large of an injector. You need something to tune them.

Yes, as I said I'm waiting on a chip right now burnt for the 750's. But if it was a fuel related problem it would show by fluctuating numbers on the WB02. Once the car is warmed up and the RPMS settle the AFR's are right around. 14.5 and steady as a rock. This mixture is not overly rich or lean IMO. So fuel is not the issue here.

I'm just wondering if the IAC can keep up with the addition of the larger maf and the previously installed BC-272 cams. I may just be flowing to much air at idle for the IAC to process. And the chip should fix this.

I know this is very common with mustangs when they upgrade MAFs, cams, TB, heads etc. They make a plate that fits in between the IAC and the TB with adjustable bleeder screws.

 

[steve]

While you have a serious issue with the injectors and MAF and no tuning device I don't think that is the cause of your surging. You changed the injectors and MAF. To put the MAF on you had to change it post MAF piping and to put the injectors in you have to touch the seals in the head. Both of these can cause air leaks and it's those leaks that are the usual cause of idle surging.

Start by pressure testing and fixing any leaks no matter how small.

 

[forcefed86]

Well it got alot better with the new chip. Roughly a 200 rpm surge or so now and it only does it at times. Seems like every 3rd- or 4th stoplight it will surge a tad. Also if I turn the AC on it surges about 450rpm. Think I'll replace the IAC and go from there.

Thanks

******************************************************************

Well I pressure tested it today. Found a pretty decent crack in the weld on my IC up-pipe. Then an even bigger leak at the BOV base. Makes sense I had removed the BOV to mod it for high boost.

So I welded the up-pipe and made a new seal for the BOV. Smeared RTV all over the gasket this time as well.

Started it up and it immediately surges. Just like it did before. Can't find any more leaks with the pressure test. I'm lost. The ISC shows 35.5 ohms of resistance. The high end of spec is 35ohms. Think the ISC could be bad? If I unplug it there is no change in idle.

 

[steve]

Started it up and it immediately surges. Just like it did before. Can't find any more leaks with the pressure test. I'm lost. The ISC shows 35.5 ohms of resistance. The high end of spec is 35ohms. Think the ISC could be bad? If I unplug it there is no change in idle.

Unplugging doesn't change the ISC position unlike other cars. It just leaves the pintle where it was. If all four coils read 35.5 ohms that would be good for one of the black plastic units. If your old ISC was bad it may have damaged the drivers in the ECU. The way I usually notice is by logging the ISC steps. If they are 0 or >120 then the ECU has been trying to move the pintle and can't get the idle under control. If adjusting the BISS doesn't bring the idle back down and the ISC steps back in line I start looking at the ECU and throttle body.

 

[forcefed86]

Unplugging doesn't change the ISC position unlike other cars. It just leaves the pintle where it was. If all four coils read 35.5 ohms that would be good for one of the black plastic units. If your old ISC was bad it may have damaged the drivers in the ECU. The way I usually notice is by logging the ISC steps. If they are 0 or >120 then the ECU has been trying to move the pintle and can't get the idle under control. If adjusting the BISS doesn't bring the idle back down and the ISC steps back in line I start looking at the ECU and throttle body.

I doubt it's the ecm. I had a newly overhauled non eprom chip in it before installing the new keydiver eprom ecu and chip. It surged the same with both ECU's.

The BISS does bring the idle up and down, doesn't eliminate the surging though. The surge is less severe the lower I set the initial idle. But the ISC then acts like it's not controlling the idle and the car will stall/die while costing, coming to a stop light, etc.

Is there anyway I can remove the ISC and reset it manually? OR jump voltage to one of the terminals to close it while it's installed? Possibly watch it to see if it's physically moving?

I ordered a scanmaster 3 two days ago so it should be here soon. Pretty sure that checks the ISC counts.

Appreciate the help.

 

[steve]

Once warmed up does the car idle at 750 RPM or whatever speed your chip is programmed to?
Have you adjusted the BISS like you need to after fixing your leaks? The FSM describes how as does the BISS VFAQ

What your describing sure sounds like the idle circuit isn't functioning. There are several parts involved. The ECU is central, it uses the Idle Position Switch to tell it when the throttle is closed, the Vehicle Speed Switch to tell it if the car is moving or stopped, the TPS to tell it what the throttle position is/was, the CAS for the RPM, the Engine Coolant Temp sensor to know if the car is warning up, and the ISC to adjust the amount of bypass air.

When starting the car the ECU opens the ISC all they way to aid in starting. As soon as the car starts the ECU closes the ISC down depend on the current ECT and RPM's. When the car is cold the Fast Idle Air Valve usually provides all the extra bypass air needed but as it closes the ECU steps the ISC to keep the RPMs set by the ECT map. If the car is sitting still with the IPS closed and the RPM's exceed the limit in the ECT decel map and it can't lower the speed with the ISC, the ECU turns off the fuel until the RPMs fall in line. You see this as idle surge.

I'm not an expert on how the AFR impacts an engines idle speed. My mental model is from messing with simple carb engines where you would adjust the idle jet to lean out the engine to the fastest idle and then back it off. Air and fuel interact to set the idle speed. I know that on a DSM most fast idle problems are from too much air bypassing the throttleplate. That can be from leaks, misadjusted BISS, bad FIAV, bad ISC, and other TB problems like the IPS being touched or the factory sealant removed from the butterfly.

It doesn't take a big leak to throw the system out of whack. Think about how little the BISS changes the airflow or how quickly the RPMs rise when you just touch the throttle. That's part of why this is such a hard problem to find and dates back to the really early days of DSMs.

 

[forcefed86]

I come from the same carb. tuning background. Sure would be nice to change a jet and set an idle screw!

That being said, I have tries BISS adjustment per the manual. It's almost like ISC isn't working at all.

When grounding the terminal on the diagnostic port should I get a CEL? Nothing seems to change when I ground this terminal? I was thinking this would possibly reset the ISC? Anyone know what it does?

I'd like to manually close the ISC if possible anyone know how to do this? IE jump power to "X" terminal?

I would think if the ECU was turning off fuel to lower the idle I would see it on my WB02? I'm seeing a steady AFR reading durring my surge. Leading me to believe it's not fuel related. As I said above I have tested IPS, TPC, etc. FIAV being the only valve I have not tested.

Everything points to a vac leak, even the suddenly spiking boost I now have @ WOT. But I can't find a leak? Frustrating to say the least!

 

[steve]

That being said, I have tries BISS adjustment per the manual. It's almost like ISC isn't working at all.

When grounding the terminal on the diagnostic port should I get a CEL? Nothing seems to change when I ground this terminal? I was thinking this would possibly reset the ISC? Anyone know what it does?

I'd like to manually close the ISC if possible anyone know how to do this? IE jump power to "X" terminal?

I've been trying to suggest that the ISC isn't working.

If you have ABS you might get a CEL when you ground the mode pin (10) on the DLC. Remember you cah to ground it and the timing adjust pin under the hood to set the BISS but if the ISC isn't functioning it won't move to the default position and you won't get the BISS set right. What the set the Basic Idle Speed mode does it move the ISC to the default position and hold it there so you can set the BISS for the correct RPMs without the ISC moving.

I'm not aware of any way short of taking the ISC apart to manually extend the pintle to close off the ISC. One test is to remove power from the ECU (unplugging it or disconnecting the battery are two ways to reset it), pull the ISC from the TB and then reconnect the power. When you turn the ignition on the ISC should rehome, stepping smoothly in and out then returning to the default position for startup.

About a quarter of the ECUs I repair have a blown ISC driver that isn't visibly burned up. When you add in the ones where C106 leaked and eat up the ISC trace running under it the number goes up to about half. That makes it common enough for me to suspect ECU issues whenever someone is having ISC problems when they have idle or stalling problem. A bad ISC with one or more shorted windings will destroy the driver for that winding in milliseconds after turning on the ignition. This is why it critical to measure the windings in a suspect ISC before putting a new ECU in or when swapping ISCs.

One thing else you can try is to disconnect the green wire from the IPS. Since the ECU doesn't test for the high idle speed when it thinks the throttle is open it should stop surging and rev until the stabilizes for the amount of air and fuel it's getting. Also make sure you have a good o-ring on your BISS and that the ISC pintle isn't coked up.

 

[forcefed86]

I've been trying to suggest that the ISC isn't working.

If you have ABS you might get a CEL when you ground the mode pin (10) on the DLC. Remember you cah to ground it and the timing adjust pin under the hood to set the BISS but if the ISC isn't functioning it won't move to the default position and you won't get the BISS set right. What the set the Basic Idle Speed mode does it move the ISC to the default position and hold it there so you can set the BISS for the correct RPMs without the ISC moving.

I'm not aware of any way short of taking the ISC apart to manually extend the pintle to close off the ISC. One test is to remove power from the ECU (unplugging it or disconnecting the battery are two ways to reset it), pull the ISC from the TB and then reconnect the power. When you turn the ignition on the ISC should rehome, stepping smoothly in and out then returning to the default position for startup.

About a quarter of the ECUs I repair have a blown ISC driver that isn't visibly burned up. When you add in the ones where C106 leaked and eat up the ISC trace running under it the number goes up to about half. That makes it common enough for me to suspect ECU issues whenever someone is having ISC problems when they have idle or stalling problem. A bad ISC with one or more shorted windings will destroy the driver for that winding in milliseconds after turning on the ignition. This is why it critical to measure the windings in a suspect ISC before putting a new ECU in or when swapping ISCs.

One thing else you can try is to disconnect the green wire from the IPS. Since the ECU doesn't test for the high idle speed when it thinks the throttle is open it should stop surging and rev until the stabilizes for the amount of air and fuel it's getting. Also make sure you have a good o-ring on your BISS and that the ISC pintle isn't coked up.

Well you were right. I removed the ISC. Unplugged the battery and installed the connector on the ISC. Had a friend turn the car and it retracted about halfway. Did it again and it backed off a bit more and stopped. Replaced the O-ring and cleaned in the ISC "hole" on the throttle body and pintle. Reinstalled. Seems to fix the issue. Set the idle per the manual. Worked great on the test drive. Pulled back in the driveway and it started surging again.

So I figure it's probably ISC related. Local autoparts store quoted me $241 for a new ISC. If I look it up on rock auto it looks like hyundai sonata's used the same sensor and I can get one for $45 on ebay? Anyone use these? Are they the same? Rock auto sells them for $75.

94-98 Hyundai Sonata 3000GT IDLE AIR CONTROL IAC Valve:eBay Motors (item 150385455589 end time Nov-04-09 13:37:08 PST)

Thanks

 

[steve]

Just look up the one for the DSM and you'll see that Rock sells new ones for about $80. Used ones are a bad gamble. The newer plastic ones don't seem to fail as often. I used to recommend DSMISC.com but you can now find them cheaper.

 

[forcefed86]

Well I ordered a new ISC.

Just for grins I removed the valve and plugged the hole. I figure if this was my problem I should be able to up the idle with the BISS and it should maintain a steady ,surge free idle.

Well with the ISC hole completely plugged, I started up the car and it still surges. AFR's are pretty steady but lean around 18:1. I noticed unless I have the engine above 1000rpm the AFR's are very lean. Right at 1100rpm I'm rock steady at 14.0-14.5. This is the same with the ISC installed. My chips idle is set to 850 to help compensate for the 272 cams.

What is "normal" afr for a 4g63?

So I removed the plug and reinstalled the ISC. Idle still surges the same. I can remove the ISC as stated above and watch it drive in and out.

I'm thinking I may have other issues.