Hello all, I have been pulling my hair out trying to find the reason that my car won't idle. 1991 Formula, 350 with a 730 repinned as a 749, the usual deal that many people seem to have had success with. 42lb injectors. Lower idle vacuum than stock from a slightly larger cam. I believe I have the BPC set appropriately, and the IAC wiring doesn't seem to have an effect on the problem. The car is hard to start, and when it does start it will stay running but as soon as I take my foot of the gas, it sits at 800rpm for a moment (where I have my idle speed set) and then it dies.

I've tried different calibrations from the stock Sy/Ty BBZB as a base, to Bin files that I've collected from various sites. None of them have allowed the car to stay running.

I know I need to hook up a scan tool and perhaps that will give me some clues as to why this is happening, but is there anything obvious that I am overlooking that may contribute to this problem? It seems as if it's an IAC or fueling problem. I'm open to any and all ideas, I'm curious if this has happened to anyone else.

If you need any more details just ask. Thanks for any help you can give me.

 

Look at the spark plug for an answer. A wideband will also help. If the engine starts, dies, and restarts without a hitch then it's more than likely too lean. When you're too rich you'll know it because it won't want to restart and you'll get smoke out the tail pipe.

 

Ok, thank you for the insight. It is hard to start after it dies, so I'm going to assume it is too rich at idle, possibly while cranking as well. Can you point me in the direction of the tables I would want to modify? Should I lower the VE numbers at low RPM and MAP areas?

Also, what BPC should I really be set at? It's a 350 bored .030 over and 42 lb SVO injectors.. I'll check my notes, but I believe I am currently at .058 (using promgrammer). Too high? Too low?

 

I haven't played with the $58 code yet so I'm not going to advise you on what to change. Before assuming it's too rich, look at the spark plugs. A lean plug will be very clean with not a lot of carbon deposits. A rich plug will be darker and way rich will be black and wet when it's fouled. Looking at the spark plugs has always been step 1 on getting a new engine to idle. It's a critical step.
As for how to richen/lean out the calibration, it all depends on what the engine does when it's warmed up and idling. There are lots of ways to lean and richen things up but some are better than others. The real trick is to first get it running and running well at idle. If you've got a "hot" engine with more cam, heads, and exhaust, you'll more than likely need to lower the VE and add some timing, 4-8 degrees. Remember though that the idle MAP of a stock motor vs a larger cammed motor might not be remotely close!
Sunday I was working on a 2 bar map 93 Lt1 stroked, ported, cammed, intercooled Lt1. That thing was really easy to get started but was too lean everywhere else. Found out the fuel pressure was turned all the way down to 30psi on the "42#" injectors. No wonder it would idle with a 32# injector constant, lol. Needless to say it was apparent that it was lean by just looking at the spark plug. Within 5 minutes of me asking question I got him to tell me the fuel pressure . Moral of the story; make CERTAIN, you're mechanically all fit and ready to start tuning. Check the fuel pressure and set the injector size, then don't touch it until you've gone and modified the VE tables on a WARM engine. This way the VE doesn't need messing with for a while and you can focus on the correction tables to address starting and cold start open loop conditions.
Some masks use pulse width modification routines that need adjusting since they aren't linked to the actual injector flow rate. In these cases you usually need to scale down the tables by a factor between 0.5-0.8 .
Good luck with the tuning and hopefully somebody with a similar setup and code will chime in to help you.

 

without a scan tool you are going to continue to struggle.

Get a scan tool hooked up and see what happens.

There are 2 main fuel tables, one close throttle 0% tps, other open throttle.

Start in the closed throttle table.

Again i wouldn't attempt anything or come to a conclusion without a scan tool.

 

Ok sir. I will pull a plug and see what it tells me. The engine actually is not stock at all, with an HSR, Trick Flow heads, SLP headers, a Procharger, etc... so it's very likely that I need to lower VE in some areas. What's interesting is it will fire up and idle perfectly with $8D, so I wonder what makes $58 different. I wonder if I should start by copying that VE table over, but then again maybe I would be getting ahead of myself by doing that because there may be some other table modifying it that I don't know about.

I will verify my fuel pressure and base timing, along with making sure the BPC is where it needs to be. Hopefully someone can chime in and tell me if I'm near the ballpark I need to be in that respect, and if there are any other tables that modify the pulse width or anything else that need to be changed. I've done a lot of searches and reading but it feels like I am missing something.

 

Good to know. It runs when I give it throttle, and dies when I let off. So this table could be affecting that. I have Freescan on my laptop so I will scan it as soon I get a chance. Thank you.

 

Tunerpro RT can scan also, the xdf and ads files are on nwstp.com for your ecm.

 

Ok, you were absolutely right.. the plugs were horribly fouled. I've replaced them, and have tried to get the car to run.. it seems to run better, but then it dies. I guess I'm not sure exactly how much VE to take out in the closed throttle table, to actually make a difference. Would my BPC vs. %EGR setting affect how much I'll need to adjust my VE tables? I've also added timing in the idle RPM areas.

Also, do I need to touch the "Min base pulse" setting, which according to Promgrammer is at 0x036A? Could this possibly not be allowing the pulse width at idle to not be small enough? I haven't really seen much talk about this, so I'll assume not, but who knows.

 

You really need to get a scan tool on it to tell much.

You MIGHT get it to idle without one, but it will take you 50 years to tune a car without one, and probably 20 motors.

Once you get a scan tool and can give me some #'s from it, we can move forward.

 

Interestingly, I was having some chip issues and found that the car would run in limp home mode, without a prom installed.

Also, inadvertently I found that the car will idle in $58 using a 1-bar map sensor, but with the chip set as 2-bar. It dies when it's set as 1-bar. I tried this after adjusting the closed throttle VE with no success. So I guess that would mean that it thinks I am running with a higher map reading than I really am, right? Since a 1-bar would put out twice the voltage at the same manifold pressure compared to a 2-bar map. (I don't have a 2-bar map sensor yet, so I've been running it set at 1-bar.)

You are right, it's definitely time to hook up my scan tool and see what's going on. I will post my results as soon as I can.

 

I think your BPC setting is too low assuming your fuel pressure is correct. You said you had it at .058 in Promgrammer. I calculate it should be .068 based on your specs. This might be why it runs when set to 2-bar in the code while using a 1-bar MAP. I'll bet you could have fouled the plugs if you tried using a stock $58 bin without first changing the BPC....just a guess, but it's easy to quickly foul a set....been there, done that!

 

Ok, now I really need help because I don't know what what would cause these problems.

First off, one weird thing - with $58, the tach jumps around while cranking and reads erratically when the car is running. With $8D, or with no chip in the memcal adapter, it doesn't do this.. any idea what might cause this? I thought it could be an ESC or memcal problem, but it only does it with $58. Also, with the car running, if I switch the AC on, the tach jumps down a few hundred RPM and the engine starts to run really rough.. does the AC send a request to the ECM that needs to be adjusted? I'm stumped on this one.

Ok, so to get everyone up to speed.. the car starts and idles now, with the BPC set at .068 and idle speed set to 800 rpm in neutral and in drive (shouldn't matter, the car is a manual and as far as it knows it is always in neutral). It seems to have decent throttle response and doesn't stall when I rev it. It is driveable.. when it is first started and cold. Then it comes up to temperature and suddenly the idle is erratic (on the verge of stalling), then it pops and backfires violently. I assume this is a tuning issue because it never had this problem with $8D... but where to look in the tune?

I have been using Datamaster for scanning but I am still trying to understand how to output the numbers I would need to post.. so far I have only figured out how to "replay" the runs in the program. Is this the desired format for you guys to look at or would you prefer something else?

Thanks a bunch.

 

When a MAP engine first starts, it takes a sec to pump the manifold vacuum down to what it will be running at. You might try adding some fuel in the 400-800 RPM areas, at 85+ K/Pa.

 

I am pretty sure I have some sort of electrical problem, that is the only explanation I can think of. Today, I started the car and it ran and idled for a good five minutes, reaching operating temperature within that time. The tach did not jump, and it was relatively smooth running. Out of curiosity, I switched the AC on and off and the tach didn't move and the engine didn't stumble like it had the day before. The ac thing sounds weird but it's the only way I had been able to recreate my jumping tach problem.

Then after another minute of the engine running smoothly, the tach reading fluctuated between roughly 3000 and 0 RPM (the engine didn't change speed) and then the SES light came on and the engine died. It set a code 42.. ESC or memcal error? Attempting to recrank the engine, the tach jumps WILDLY and the engine does not start. Wait 10-15 minutes and it starts up fine, and the process starts over.

Now, I thought maybe I was burning my chips incorrectly but then wouldn't it have set the code immediately? I have tried stacking the bin, and burning the bin at $4000, no difference. It also does it with both of the V8 memcals that I have. Do I have something wired incorrectly, or could some electronic part be overheating and causing problems? The distributor, pickup coil, and ignition module are all new, also.

 

Hm, could a bad/loose connection at pin D5 cause the tach to move around wildly and a code 42 to set? That pin is right next to the injector ground pin that I moved when I repinned for $58. I have a hunch...

 

Ok, forget about D5. I meant D7, which is the EST bypass wire. I found that I had it connected to D6. I fixed that, so now I have no code 42 and I now have spark advance at idle. That could have easily been contributing to the car running rough and being on the verge of dying, I never thought to verify running timing with a light, all I had done was verify base timing. Thanks to all that have helped me so far, this has been a big step in the right direction to getting my car on the road.

Now it sets a code 35 for not being to control idle, looks like I need to verify my IAC wiring once again, maybe change it back to the original configuration..