Hey,

I recently bought a ported intake set off the classifieds, and just finished up the swap this weekend. It's a ported Edelbrock intake, ported SLP runners, and ported '90 plenum. Before doing this swap, car ran fine, consistent 15.1x-15.2x, but I couldn't pass up the deal. So here's the scoop.

Got everything put back together, all vacuum lines back on, sensors plugged in, distributor set close, all that good stuff. Started up the car, it started right up, but died right out. Tried moving around the timing a bit, but nothing would keep it running unless I kept my foot in it. Thought maybe I had a vacuum leak. Re-tightened everything, made sure my vac lines were all on snug. The '90 plenum uses an extra port for a MAP sensor, but that's been capped. After tightening everything up, I have the same results.

This leads me to think it's something with fuel, but I don't see how. I didn't change anything with the fueling, why would doing an intake swap mess with that? Never touched the IAC, TPS is set at .51, close enough to .54. Getting a fuel pressure gauge on there tonight, but any ideas in the meantime? Thanks!

Update: Car runs, idles, etc. When warm, it starts hard. Have to put some pedal to it. Also, I can rev it up to 5k easy the first time, then the next few times the tach moves up very slow. On the road, it's just terrible. WOT and it has almost no pull. Could a loose distributor cause this? My bolt bottomed out just before the dizzy was tight, just enough that a force of hand can spin it. Could this be the problem?

 

Take the runners back off and make sure the gaskets are all lined up right

 

That was one of the first things I tried. I suspected vac leak because the bolts were too long and bottoming out. I trimmed them down and put the runners back on with the gaskets already on supported by the bolts.

Could it possibly be the injector o-rings? Completely forgot to replace them while I had the fuel rails off.

 

Where is your base timing? What does your vacuum read at whatever idle you can maintain?

 

Roughly 6 degrees. It's been tried over a fairly wide range though. Can't hold a steady rpm at all. It either dies out without any pedal, or surges up to ~4k and back down to 1k with my foot on it. It just cycles like that. No consistency at all.

 

If you are certain there are no vacuum leaks or fuel leaks anywhere, and if your timing is set at 6-degrees with the EST disconnected, then your right, there shouldn't be a problem if the engine was running fine before the swap. Disconnect the battery to reset the ECM, then when you reconnect the battery, disconnect the MAF sensor and start the engine. Are you able to at least hold an idle this way? If not, it's either the manifold not seating properly on the heads, a fuel pressure issue, or your spark plug wires are on wrong...

 

Plug wires have been redone twice since the swap, so that's out. I'll try disconnecting MAF after I get off work and post results then. Do you think the injector o-rings would have anything to do with it?

 

If the injectors didn't give you an trouble sliding back into bungs on the lower manifold, then no, I highly doubt there is a problem with them. I usually coat the o-rings with a little petroleum jelly, but again, if you don't smell fuel, and don't see any fuel trickling out anywhere then I doubt there is a fuel problem, unless there was a pre-existing problem somewhere. Pull the MAF and see if she idles more stable. If it makes no difference, and you are positive that your timing and wires are set properly, that fuel pressure is good, and that there are no vacuum leaks up top, then I would seriously look into the intake manifold flanges and make sure they are not warped or cut in any way creating a vacuum leak underneath the manifold (being that this all occurred with the manifold swap to begin with)...

 

You got it, pulling the MAF sensor got her to idle a bit. Also should note, fuel pressure came back at 43.5 psi fuel pump primed but not started. What's my next step then, if it has to deal with my MAF?

 

Also should mention, before the swap, I was lean at idle in closed loop. No wbo2 sensor, but blms read 140-150. Am I just running too lean right now since I have a much better flowing intake system? I don't understand why unplugging the MAF would get it to idle. Can you elaborate?

 

Andrew are you sure there are no codes being tossed your way? Every last wire is hooked up? From what I learned when there is no MAF reference, your in limp home mode?

If you believe your too lean it only takes 1 minuet to add say 118% fuel in the areas where you saw the 150 blm at idle. 150/128= the % of fuel you need to add for the respective areas and use averages over the RPM MAF tables that you recorded. But if you cant get it to run then just throw some chunks of fuel in there and see what happends, it wont hurt to try IMO, since i have no clue also on what else could be causeing your problem.

Ive read a few threads like this below. About if the car will run without the MAF.

"It should be able to. Unplugging the maf forces the computer into limp home mode and uses fixed tables, iirc, for the fuel. It should not only run it should be able to drive decently, considering.
I can't remember offhand the power flow through the relays so if one is fried it may kill something else, somewhere else"

Ive only had my car in limp home mode after extensive mods and I know it literly "barly" ran. Just enough to get it to the side of the road if it came to it.

 

You said your BLM's were reading 140-150 before the intake swap, but what was the INT reading? If you were lean to begin with, a better flowing intake manifold will only increase the amount of air that the combustion chambers are taking in... but not by much as the air is still being pulled in through the same size throttle body bores. Regarding high BLM's, either you have a very substantial vacuum leak, your injectors are too small for your tune, you have a few injectors that aren't opening, or your fuel pump is on its' way out. If your injectors and fuel pressure are okay, then look towards the O2/MAF sensor as being faulty because something is skewing data and telling the ECM to pull fuel when it shouldn't. As a test, with the engine idling, touch each injector and feel for a thumping "pulse". If your having trouble feeling for a pulse, or simply can't tell, with the engine idling pull each injector harness individually and listen for a change in idle. If there is no change at a particular injector when the harness is removed, then the injector is more than likely dead and isn't providing fuel. Check the condition of your spark plugs too, as the condition of them from running that lean will help you pinpoint which cylinders aren't getting fuel. As for unplugging the MAF, the idea behind that was to see if the engine will be able to maintain an idle, and help you to eliminate any possible vacuum and/or spark problems. From the sound of it, it sounds like a fuel distribution problem causing your high BLM reading, and that can be caused by either a mechanical problem (bad fuel pump, bad regulator, bad injector-s), or a bad sensor that is skewing data being sent to the ECM telling it to pull fuel (bad O2/MAF sensor(s), etc)...

 

I think I know what it is then...my MAF shouldn't be bad, as the car ran fine before, I just assumed the high BLMs were from me having an open air filter as opposed to the stock metal canister. But now that you mention it, I'm thinking it's my o2 sensor. I recall reading a thread that mentioned needing a heated o2 sensor for headers, because the bung is in the collecter, much farther down than the stock location on the exhaust manifolds. Something about the exhaust traveling farther before it reaches the o2 sensor, and it being cooler than when located in the stock location. Do you think that might be what it is?

Warmed up at idle 625 rpm, I have a BLM of 149, and an INT of 138.

So, by unplugging the MAF, I eliminated vacuum leaks and spark problems? Just want to clarify. With fuel pump on, ignition off, I have right around 43-44 psi. I'll check the injectors though. What gets me is that the car ran and idled before the swap, and now it barely does. If something was going bad with my fueling before, why would it take effect now? Like you said, I shouldn't be pulling in that much more air, because it's still going through the throttle body bores. Is it just more along the lines of "the car needs more fuel, but a bad sensor/fuel part is keeping the car from getting it?"

Like Mark said, would adding fuel be a "quick fix" until I get a wbo2 sensor or whatever else is the bigger fault? Next Saturday is a pretty big event, and I'd like to be racing for it.

Also Mark, only codes I get are EST when it's unplugged to find base timing, and MAF when that's unplugged. Other than that, no codes.

 

Are you running a catalytic converter? If not, that might be an issue then, as less back pressure equals less heat, but the only way of knowing for sure... if you want to eliminate that as a possibility, would be to aim a laser temperature gun at the O2 bung and literally see how much degrees that area is reaching.

While your at it, check for exhaust leaks before the O2 sensor...

Yeah, that's lean. Bump up the fuel pressure some, if you don't have an adjustable fuel pressure regulator, either convert the stock regulator to an adjustable one, or just remove the stock cover and put a quarter on top of the spring to increase pressure a little. Either that, or burn a new prom and add the necessary fuel...

What is your fuel pressure with the engine idling? The stock ECM can only correct up to a certain percentage, so either the ECM has reached its' limitation, or there is a sensor giving skewed data causing the ECM to pull fuel. Are you surging in Closed Loop only with the MAF connected, or at all times the moment the engine is started...?

 

I don't have a cat anymore, it was removed when I put the headers on, along with a cutout, so that's definitely a possibility. I'll tighten up my header bolts though.

I'll burn a chip now, as I just got home. The car hasn't been in closed loop since the intake swap. I'll also let you know what my fuel pressure is with the engine on.

 

Tightened up the header bolts, started up the car with MAF plugged in. It ran really really well for about 60 seconds, then I turned it off. I did find one vac leak though, had a rubber hose going to the cruise control had a slight hole in it. Wiggling it around I could hear hissing every now and then. Fixed that. Back to what it was doing with MAF plugged in before though, except I can hold an RPM fairly consistently. It just won't idle though. PSI is reading about 40-42 with the engine on at any given RPM, it flickers a lot, but always in that range. Going to check for more vac leaks though, I can hear a hissing noise, but I always just assumed it was my air filter, as it started to hiss once I put the open K&N filter in place of the metal canister.

 

@Rob what are those injectors maxed out at verses the pulse width? Arround 10-11?? I cant remember but that would help him know if he has a fuel pressure problem, by looking at what hes running and what is the high end of the BPW.

Andrew spray away with carb cleaner and find the leak....

 

Is the intake getting super hot? Edelbrock just went through a bad batch of tpi intakes where they drilled a hole to far from the drivers side runner into the egr passage. My car wouldn't idle or hold vacuum. Just something to check

 

I got mass injector o rings for ya so I hope that helps as you did see that you have a leak there.

 

I should have done the o-rings on the injectors, seems like it's got a leak there. Spraying ether made it surge, so I suppose that's the next step. I don't think it's solely that though. Not too familiar with the MAF tables, how much of an increment should I bump them up by? I don't really want to just add a chunk, as it might go too far the other way. It would be much easier with a wbo2 sensor, but I won't have one within a week lol. I just want to get it fairly close to a good idle A/F ratio. It was lean to the point of stalling out every now and then before.

 

Divide you average blm by 128 for the cells. So if you get say 150/128 then that would equal 1.17. Hense you use the multiply tool and mult the existing value by 117%

Im still no help on where you add the fuel as those MAF tables..I have no experience on at all. Search search on here and google asap and youll find out im sure.

One search and I found this so theres alot of stuff out there if you need info right now https://www.thirdgen.org/forums/diy-...djust-maf.html Threads like this should at least help you and me also understand the concept of MAF. I sure wish you had speed density...LOL

 

Andrew Id also like to add this about your MAF set up.

When disconnecting the MAF will put the fuel system in default(Memcal) mode and it will run on a default fuel map using throttle position as a reference. A car with no other issues will run okay this way. Disconnecting the MAF and running the car to check for normal running is a commonly used test for a faulty MAF sensor.
That just means that your MAF does work correct. Just for future reference of your set up and if you wish to see if the senser works correct.

 

Might stop over tomorrow Mark for those O-rings. My plans kinda fell apart for tomorrow. Gonna spend some time at the Pontiac Nationals though. Hopefully I can have the bird pieced back together tomorrow and running correctly. Only took me about 20 minutes to do a teardown, with the engine still warm lol. Hopefully I can get it back together that fast. I'll give you a call tomorrow though.

 

@Formulakid. I'm not sure if I have a bad one or not. It hasn't really been ran enough to get hot. I bought it from a member on here who bought it from someone else on here, so it seems like it's been out a while. How recent was this bad batch? I'll look into that if these o-rings don't fix the problem.

 

Do believe I found the problem. O-rings looked brand new, not the problem. However, to get to the O-rings, I had to pull the runners back off, and I noticed a few things goofy. The gaskets I had to cut were backwards passenger-driver side. Just barely. Where the cold start 9th injector would go on earlier motors, there was an extremely tiny sliver that the gasket didn't cover. Without looking at it good and hard, you'd barely notice it.

That wasn't the full problem though. Turns out, the bolts the guy sent me were different thread pitches. 4 of 1.25 which are correct, and 4 of something thinner. My runners weren't sealing fully around the bottom. Putting them in the first time, it seemed like the bolts he sent me were bottoming out. I trimmed them down a bit, thinking the bolts were just too long. Actually, someone else had previously put the smaller threads in, and screwed up the bolt hole threads. Fixed this using a tap, thank God bigger threads are forgiving, but I'm still short 5 80mm 8x1.25 bolts. Picking those up tomorrow. If the problem persists, I'm out of ideas really. There shouldn't be any vac leaks anywhere around the intake/lower runners, especially with some help of excessive RTV

 

Autozone has tons of those bolts. 8M 1.25 If thats the size your talking about. There about a 4 bucks for a 4 pack. Generly I think almost all the bolts on my car are 1.25 in pitch.

Glad you found the problem!

 

Hopefully it's the problem, won't know until tonight though when I get her all back together.

 

I replaced my EGR valve once... put everything back together... started but wouldn't idle. Spent days checking out the electrical. Eventually paid a GM mechanic to look at it. Vacuum leak.... Exactly that behavior... turns out my runners were on backwards so I can totally see that being your problem. Someone suggested doing the spray can test with some flamamable gas... see if it surges or something.

 

For a long time I wasn't sure which runner was which, they're very similar. The SLP ones have the 9th cold start injector tube sealed though, that's what gave it away. My problem wasn't the runners though. Just the gaskets. Very slight difference, just enough to cause the problem (hopefully that is indeed the problem). I'll be home in about 2 hours, hopefully the bird runs in 3

 

Once I was told the problem... had it towed to my dad's work and took me all of an hour to switch the runners back...

 

She runs now, after a bit of adjusting with the base timing. Apparantly my bolt for the distributor is too long though, as it bottoms out before fully tightening the distributor down. I have a bit of oil around there.

What would cause the car to start really hard, and have really poor throttle response intermittently? I can gas it the first time, and it'll rev right up to 5k, then the next 2 or 3 times it'll take a few seconds to reach 5k. Could it just be too lean? Would that account for both the long start and the bad throttle response? TPS set at .51-.53 volts, IAC was never messed with since I've had the car.

I'll get a datalog and post it tomorrow. I'm certain it needs more fuel especially at idle, but I'm wondering if that's the root of my current problems. Thoughts?

 

Attached is a Closed Loop datalog. Notice the incredibly high BLMs and INTs. Is this lean condition what's causing my intermittent very sluggish throttle response? Or the rough start?

Beware, I exported quite a few of the parameters, as I wasn't sure exactly what you would be looking for. I kept out small stuff like codes, A/C, etc, since they would just take up more spreadsheet slots.

First thing I'm doing is adjusting the MAF tables to get my BLMs/INTs to 128. Any other suggestions?

Also, ignore the glitches here and there in the log. They're identified by all numbers across that time being skewed. Not sure why it glitches like that.

 

Also clean your maf sensor wire.

 

Adjust Idle First in closed loop, then your part throttle, then your WOT throttle. Wish you could borrow my Wideband as it would really help the accuracy and speed up the process.

 

I adjusted idle fueling by 1.125x (144/128), but it didn't seem to help any at all. It actually stalled out twice. Driving down the road at WOT, it had barely any pull. Ideas?

 

MAF was working fine before the intake swap, but I cleaned it up with MAF cleaner anyway. No change.

Re-set the base timing with EST unplugged, 6 degrees on the nose. Car doesn't seem to like to idle with EST plugged back in though, after clearing the code. Perhaps my spark advance table is set too high at low load/low rpm? I'm shooting in the dark now really. Re-checked fuel, 43-44 psi.

Or perhaps I need to add fuel at higher load/rpm? The car starts easy first time around, anything after it starts rough. Once it idles though, it's smooth. When I first gas it to 5k, it moves right up. Next few times, it's very sluggish getting up to 5k. On the road it has very little pull until about 4k rpm, and takes forever to get there. Also, I'm getting a high TPS code every now and then on the road, but it's set at .51 at idle. Thoughts?

 

I had a problem with a truck I used to have... throttle problem. It would bog down under load but fine just reving in nuetral... 4 cyllinder with 8 plugs... and while I never got it diagnosed... someone suggesting it was an ignition problem.... distributor, plug wires, coil. Maybe under load and RPMs the coil isn't able to build enough juice? or something like that.

 

Would a loose distributor cause this? I had to trim down my dizzy bolt for the Edelbrock intake, and I didn't trim quite enough off. Bolt is bottoming out, but dizzy turns with a little force of hand. Fixing this today if I can get a wrench on it...It's proving very hard without a distributor wrench.

 

Maybe, not sure... but you can make a distributor wrench with a torch and a vise and a hammer