Closing in on a problem

**1great40** · 08-30-2014

Jim, The PROM says AKMH

**1great40** · 09-01-2014

First of all, let me take a minute to thank all of you guys who have commented and made suggestions about the problem I'm trying to troubleshoot. I'm in over my head here, but I feel less so because of the effort you're all making to help me. Hopefully, someday I will be able to constructively comment and help someone else here, but don't hold your breath :)

I have a gauge permanently mounted in the fuel line under the truck. This morning I fired the truck up and backed it out and checked the gauge. The needle vibrates some but it's reading about 11 1/2 psi. Which is right where I set it when I modified the stock fuel pressure regulator to work with the Holley inline pump. So, I'm guessing that the lean condition at idle is probably not from the fuel pressure.

I'm wondering however, the truck engine is bone stock with the exception of a 2" full dual exhaust with a crossover pipe and no cats. I remember well an old nova my brother had which had a habit of loosening the nuts that held the head pipe to the manifold, That thing would run like crap till the pipe was tightened.

I noted a small exhaust leak between the head pipe and the exhaust manifold, you couldn't hear it (well at least I couldn't) but you could feel it puffing out. This is on the side with the o2 sensor and it's ahead of the sensor. Obviously I'm going to fix that pronto but I'm wondering if there is sufficient backpressure in the exhaust system for the way the stock engine was calibrated. If I were to plug one pipe and force the exhaust from one side through the crossover tube and have everything come through one muffler, what should I be looking for as far as a change in values that I would read while logging data? I think it couldn't hurt to try that and then I'll post up another datalog. Then the all knowing sages of Gearhead-EFI can tell me if I'm deeper into the toilet than when I started.

**jim_in_dorris** · 09-01-2014

When I first got my PU, it had dual exhaust, no cats, not crossover. I had to add cats to get emissions legal, and noticed a huge improvement in how it ran. I can't say what yours will do, but plugging 1 side and forcing the exhaust out the other shouldn't hurt in the short run. The exhaust leak up-stream of the O2 sensor however will show lean, so fix that.

**1great40** · 09-01-2014

Tell me if I'm all wet, but from what I have read, I would have to actually run and drive the truck somewhat to see a change in the way the engine runs and data returned from the ECM. If I'm understanding things correctly, after some driving time, the BLM number should have shifted, indicating that the fuel trim numbers that the engine is working from are different. Is my understanding correct?

**jim_in_dorris** · 09-01-2014

Yes, fuel trims are learned over time. When I finally got the correct BIN in my ECM, I had to drive around for about a week to actually see the BLM's start to come close the where I want them.

**1great40** · 09-02-2014

I repaired the exhaust leak at the manifold. Then I stuffed a rag into one tail pipe and installed a cheapie tail pipe expander so that the rag couldn't blow out, effectively making a single exhaust system. Then I drove the truck about 40 miles. There is a marked improvement in the idle. In fact I would go as far as to say that it runs about as good as a pre-balance shaft 4.3 ever would. I will continue to put some miles on it and do another data log. It will be interesting to see if the idle AFR is where it's supposed to be, or at least close. This would certainly be the smoking gun as far as low backpressure causing a lean idle condition. If it's the case, now I have to become a tuner and figure out how to compensate the AFR for the dual exhaust, or just put a single exhaust system on the thing and be done with it. Once there is enough data gathered about the exhaust change, I would be curious to go back to the chip that Mark made for me to see how it runs with the single exhaust. The chip he made is supposed to bump up the idle speed and was modified for no EGR, AIR, and canister purge.

**1great40** · 09-07-2014

There's now about 200 miles on the makeshift single exhaust system and the engine idle is consistent every time I have used the truck since the change. I'm thinking it might be enough driving time to do another data log. I'll try it this afternoon and post it up, hopefully Jim or someone else who understands this stuff can comment on it. Thanks.

**1great40** · 09-09-2014

I took another couple data recordings tonight. When I first started looking at the data live, the number for the BLM was 151, I think that's a little lower than the first data log I did but the number was still in red, so I'm assuming that it's not a great value. A few minutes later I noticed that the BLM number had dropped to 141 and was no longer red, I'm assuming that this is a step (or steps) in the right direction. I'm am uploading both sets of data. Hopefully someone can comment on this new information. If it does show that the AFR is not as lean as before, this would indicate the dual exhaust does not have sufficient backpressure for the calibration that I have. Thanks for looking at the data.

**dave w** · 09-09-2014

The ideal BLM number is 128. Numbers above 128 are lean. The bigger the BLM above 128, the leaner the engine is running. Numbers below 128 are rich. The smaller the number below 128 the richer the engine is running. The BLM average in the two data logs was 141, which is lean. Usually BLM's between 123 ~ 133 are considered acceptable.

The INT is averaging close to 128, which is good.

I think (1.0 PSI) more fuel pressure will help get the BLM's closer to 128.

dave w

**jim_in_dorris** · 09-09-2014

I agree with Dave, try bumping your FP up. I think you should read the sync vs asynch thread on this forum. Almost all the 4.3 bins are asynch and are hard to tune. I think ony found a 4.3 synch bin, APAA or APAB that may make tuning easier.

**1great40** · 09-10-2014

Thanks for looking at the data. I should not have a problem raising the FP up a pound. I will post again after I reset it

**1great40** · 09-14-2014

Hi, I read lots of stuff about synch/asnych on here and frankly, I'm more confused than before! in any event, I did bump the fuel pressure from 11.5 to just under 13 PSI. Like I said, the gauge vibrates a bit so a perfect read is tough. I would have done it sooner but I had forgotten what type of screw I used when I modified the stock regulator in the TBI so I had to pull the whole injector pod off to remember I slotted the factory screw.

**1great40** · 09-18-2014

Well, I have run the truck about 100 miles since I upped the fuel pressure. I did another log tonight. When I was monitoring the BLM was at 144 which I guess is a step backward. Then while I was recording the data, the BLM jumped up to 146 and the value displayed in red again. I take it this is not a good sign. I'm wondering if another bump in fuel pressure is warranted?

Here's the data:

**dave w** · 09-18-2014

Originally Posted by 1great40

Well, I have run the truck about 100 miles since I upped the fuel pressure. I did another log tonight. When I was monitoring the BLM was at 144 which I guess is a step backward. Then while I was recording the data, the BLM jumped up to 146 and the value displayed in red again. I take it this is not a good sign. I'm wondering if another bump in fuel pressure is warranted?

Here's the data:

That was a very short data log.

Anyway, there are not many options available to you? Changing fuel pressure only? I think the best option for now would be to add more fuel pressure, maybe 15 PSI or 16 PSI. The first and foremost challenge to tuning is getting the Base Pulse Width (BPW) correctly set. Changing the fuel pressure to a higher pressure has the same effect as increasing the BPW, which will lower the BLM's.

Having the ability the make changes to the PROM programming is very helpful, maybe even mandatory for your TBI system to run correctly? You have made great progress in getting data logs posted!

I don't think it was a step back, I think it was a huge leap forward to learn TBI tuning ... trial and error.

dave w

**1great40** · 09-18-2014

Thanks! I guess it's true that without the ability to make changes to the programming, all I can do right now is bump the fuel pressure. I'm having a bit of a problem with the whole concept of "tuning" though. The engine is bone stock, with the exception of the exhaust system, so I need to be sure that I'm not masking another problem by trying to tune my way out of it. I'm just being cautious here and trying not to change a whole bunch of stuff at once otherwise I'll never know which change has which effect. It is an interesting way of doing things though with a computer as opposed to wrenches! I will up the fuel pressure a little more and see what happens. It seems to make sense that in the absence of making the injector pulse width larger, higher pressure without lengthening the pulse should yield a richer mixture.