I've just installed some brand new injectors from FIC. Although they are new, they are the exact same model as I had on the car before (bosch III). After putting them on, however, I'm having a strange issue that I can't figure out.

The car idles very well, but it smells very rich. Tunerpro indicates the BLM is stuck at 160, the INT is also stuck at 150, which as I understand indicates a lean condition. The engine revs up great (in neutral), and sounds very healthy. When I rev the engine the INT will come down significantly but it goes right back up.

The car jerks around at low throttle inputs, at any RPM. It feels very similar to when a park plug boot came off partially and caused a random misfire. The odd thing is under load the misfire seems to clear up. If I bog the engine at 1k RPM is 5th gear, it accelerates smoothly, and it accelerates smoothly and very powerfully at WOT. Under load, both the INT and the BLM will come down into the low 30's. The idle also sounds fine, and is very very smooth.

Based on this information I am led to believe there is a misfire causing these problems.
I have checked fuel pressure, both with a running and non-running engine. I have new plug wires on it already. I know the ignition coil and distributor are working as they should, timing is good unless it miraculously changed itself (set it when the engine was running good and haven't touched it). The O2 sensor seems to be working properly. It is oscillating as it should. I haven't touched the exhaust since it was running good, and therefore doubt there are any exhaust leaks. I checked for vacuum leaks.

Two of the spark plugs on the drivers side are black, as you would expect a rich plug to look (1 and 3). Two others look cleaner. (5 and 7)

I'm really not sure where to go from here. Any advice or thoughts about what would cause something like this are appreciated.
The car is a 1991
Thanks!

 

When you say the "same model", do you mean the exact same p/n? Or just a different p/n but still Bosch-IIIs? What is the rest of your setup? Stock? Or modified?

With your old Bosch-III's did you have the chip tuned for the voltage offsets?

So, the reason it smells rich is likely because the side with the O2 sensor (driver side on a Vette?) is telling the ECM that it needs a lot more fuel. Perhaps due to a single cylinder misfiring. The rest of the engine doesn't want that much more fuel, so you get the rich smell.

One thing you could do isolate a misfire is to let the engine idle and remove one injector plug at a time. If you get to cylinder where it has little to no effect on the idle quality, you probably found the anomalous cylinder.

If you want, export a .csv file of your log and post here. I can take a look at it...

 

They do not appear to be the same part number. They are both yellow body 22lb bosch III injectors, and they look exactly the same. But the OLD ones have F6VE-A5A on one side and
0 280 155 710 on the other. the NEW ones have F4SE-A1B on one side and 0 280 155 700 on the other.
The rest of the car is basically stock. It does have straight pipes, a 4 wire O2, and heads, but it still has stock exhaust and intake manifolds, so I doubt those are making any difference. The EGR and AIR system are also gone.

The chip was tuned for voltage offset, I'll include the BIN I'm using so you can have a look at that.

I am thinking you are right about this. The O2 is in the driver's side so I've focused on that. I'll post a picture of the spark plugs. They're in order 1-3-5-7 from left to right. I will unplug the injectors to isolate them tomorrow, that could be helpful. I don't think it's misfiring at idle however. The idle sounds and feels amazing, I will try it though.

Look at the post below for files and images, I had some issues uploading them so I posted them seperately

 

1-3-5-7 from top to bottom

 

Yeah, those look seriously rich.

Have you looked at the passenger side plugs yet?

Your .csv file is corrupted somehow...the data in there is gibberish. If you have the native xdl output log file from TP, send it to ultm8z@yahoo.com

Your offsets in the bin don't quite match what I have on published data (see attached)... but it's not way off. I don't see that causing your issues...

How is your fuel pressure?

A vacuum leak on a MAP car would really only be a problem if it was affecting one cylinder. Ordinarily on a MAP car which doesn't measure airflow directly, a vacuum leak would just be another source of idle air (like the IAC).

But if it was a local leak at one cylinder, it could result in the symptoms you're experiencing... At idle, a vacuum leak at one cylinder is a relatively large % of the total airflow into that cylinder.

 

I have not looked at the passenger side plugs. I figured that since the O2 was giving me lean readings I might as well only check the driver's side. The passenger ones are a pain to get to. I will though if you think it would be beneficial.

I'll send you the XDL, and tomorrow I can adjust the injector offsets. Even if that isn't likely to be causing the problem.

Fuel pressure is a little over 40PSI with the engine off and at idle. With the engine off it holds pressure fine and doesn't leak down. Unplugging the FPR causes the pressure to increase as it should. Unfortunately I can't really look at the pressure while I'm driving because the hose on my gauge isn't long enough. I would think that low fuel pressure would cause problems at WOT and load though. At WOT the car is just as powerful as it has ever been, and is perfectly smooth, and sounds great.

Where would a vacuum leak at one cylinder come from? I sprayed some carb clean around the intake manifold gaskets, which did nothing. I'm not sure where else to look for a leak. I do have a homemade smoke tester I can put on it, but all that's been removed since the last time I tested it was the plenum, runners, and fuel rail.

 

Well, there a few ways to get to high (or low) BLM's... one could be a malfunctioning cylinder, which would have to be on the O2 side since that's the only side the ECM can see.

You could also have a bad sensor or something that would affect the entire engine. If you can get at least one or two plugs out from the passenger side, it'd be somewhat representative of the passenger side and could offer a clue.

But before you do that, let me take a look at your tunerpro log file.

A vacuum leak at the bottom connection of one of the long tube runners could potentially impact just that one cylinder.

I doubt its your fuel pressure based on what you're saying...

 

I have sent you the log file. I'll pull a couple plugs real quick and take a look

 

Passenger side. 2-4-6-8 left to right. Tell me if you disagree, but these don't look rich at all to me.

The thing I don't understand is even if the right bank is lean, the O2 sensor wouldn't know that. I'm not sure how one side would run rich and the other lean.

 

double check the email address you sent to... I haven't gotten anything. Should be ultm8z@yahoo.com

Hard to tell from the photos, but the driver side looks worse to me.

Yeah, on a batch fire system, the entire passenger side running lean with the driver side rich doesn't seem likely... at least on a long runner TPI. I've seen it happen on short runner manifolds like the Miniram though (the infamous "split-BLM" issue).

I guess I'll have to take a look at your log file once I get it.

 

I’ve sent it again. Have you checked your spam folder? The email was right the first time. If it still doesn’t work I can try to convert it to a .csv again. My computer is dead right now so I’ll have to do it later.

 

This time it came through... wierd.

Any rate yeah I'll look at it later today.

 

on the driverside, something is causing the 02 to see excessive unburned oxygen, therefore its adding fuel globally (the only way it can) in an attempt to bring the stoich ratio closer to 14.7:1.

focus on what can cause unburned o2 to pass over your o2 sensor.

i had this on an 85, which was tough the diagnose with tunerpro due to limited scanning flexibility. Anyway, while installing injectors, one of the harness connectors had its wires pulled out, but under the rubber boot. this resulted in that injector not firing. it idled with a bit of a hood shake because it was on 7 cyls. It ran though. and i drove it for a week like that.

When i retraced my steps, i discovered that id inadvertently removed the blade plug from a connector.

The non firing injector meant the oxygen from that cyl was passing over the o2 sensor. The comp said “im ultra lean” and began dumping fuel. which did nothing to solve the issue. the car wasnt idling high, which was my clue the “lean” condition wasnt a vac leak.

Some food for thought.

 

So looking at your XDL file, you have more than just a low-throttle issue...

I plotted your BLM history for that run and you're up at 160 across many of the cells. Picture 1 below. It also seemed like the other cells were on their way up higher by the time the log ended. Generally speaking it seemed like the higher the sample count in each cell, the higher the BLM (i.e., the more times you passed through that cell, the more time the ECM had to react with the fuel trimming)

Given your plugs appear to show rich, it seems like something is fooling the ECM into adding a lot more fuel.

One error code for being too lean (as you might expect).

The only thing I find questionable is the MAT sensor reading. It's showing only ~77F. Coolant temp is about ~200F. How long was the car running when this datalog was taken? I assume your MAT sensor is in the plenum like on stock TPI?

For a TPI with the MAT sensor in the plenum, for a fully warmed up car I would've expect the MAT temperature to be closer to the coolant temperature.

The only counter-intuitive thing is, if the MAT sensor is reporting too low, the ECM would react by putting in more fuel thinking the air was more dense... But when the O2 sensor sees the end result of that and finds it was running too rich, the ECM would react by pulling fuel out, which would result in lower BLMs, not higher.

Things that could fool the ECM... Exhaust leak introducing more O2 into the exhaust stream... bad O2 sensor or an O2 sensor gounding problem (the O2 sensor relies on it's metal-to-metal connection with the exhaust manifold for sensor ground), One or more injectors that aren't flowing as advertised etc..

As an aside, you are getting quite a bit of knock retard kicking in (picture 2 below)

 

Sorry I should have mentioned before - the MAT sensor is not in the plenum its placed right after the air filter, on top of the radiator. I am pretty well sure there's no exhaust leak. I could be wrong though. I'll take a look. I did check the O2 ground but the sensor could be failing? It's relatively new but it can't be discounted. Does it look to you like the O2 is oscillating as it should? It seemed to me there were several times were the cross counts kind of stalled, and I'm not sure if that's normal. I think acceleration was causing that.
I can also do an injector balance test but probably not until next weekend.

Do you think the knock retard is indicative of an actual lean condition? The passenger bank plugs are making me wonder if the engine actually is running lean. maybe the driver side was fouled while I was still dealing with clogged injectors. It did smell rich, and it's backfiring (through exhaust) quite a bit. I've been through an extreme lean condition in this car before and it was not like this.

I'll start making a list of things to do, I have very limited time / energy for it throughout the week but I can get back to it on the weekend.

 

I just went out and checked all the injector connectors. They are all in good shape. I also unplugged all 8, and all 8 had a significant affect on the idle, so I don't think there's any misfires, at least at idle.

I DID FIND AN EXHAUST LEAK
I feel very foolish for having overlooked this
It is created by a sloppily removed AIR system. I assumed that it was fine because the car ran just fine after I removed it, which has been many months ago now. That just goes to show what happens when you make assumptions. I can't tonight, but I will figure out how to plug that leak up and see how things change. I'll let y'all know how it goes.

 

Innnnnnteresting.... lol... you relocated the MAT sensor.

This may be starting to make sense now. You may up against a tuning issue. I don't know all the history of when you noticed the high BLMs vs when you relocated the MAT, vs the current condition of the spark plugs... sounds like the plugs been through a couple of previous malfunctions, so I'm not sure what to make of the current readings...

But in terms of tuning....

There are two tables in the 8D calibration that deal with MAT's impact on fueling. Going back to look at your bin, you're still running the factory settings on these, but you need to re-tune when you relocate the MAT, otherwise you're going to confuse the ECM.

MAT Compensation Counts vs Manifold Temp => This is fundamentally what the ECM uses to factor in air density into the fueling calculation.

Inverse MAT Term Lookup Multiplier vs Airflow => Because the TPI's had the MAT sensor in the plenum, it suffers from heat soaking. The lower the airflow going through the manifold, the more the sensor reports the temperature of the metal intake manifold (which is effectively at coolant temperature). The higher the airflow, the more the air is able to cool the sensor down to match the air temperature.

Two options for this table when you relocate the MAT sensor...

1.) Disable the table altogether. In the Switches, there's a switch for whether you want this Inv MAT Table enabled. Option 1 is to disable it. That's what I did with my Miniram when I had to relocate the sensor. You may need to re-adjust the VE tables because this tends to make it run a little more on the rich side. But it's good for a more performance oriented tune rather than emissions or fuel economy. Since my '71 Camaro is not an economy car, I didn't care...lol.

2.) You could try putting in the Inv MAT values for an LT1 Corvette, which also had the sensor in the air tube ahead of the throttle body. My experience tuning on the Miniram indicates that (despite the different ECM's) the software code between the DA2 Vettes (92-93 LT1) and the 8D Vettes (90-91) is largely the same. I've copied and pasted so many of the fueling values from DA2 to put in my Miniram'd 8D and it works beautifully... especially the accelerator enrichment.

In the tables below, you have DA2 on top and 8D on the bottom. You can see at the lower airflows, DA2 has lower numbers. The lower the number, the less the ECM factors the coolant temperature into the final MAT temperature calculation. At the higher airflows, the two tables get closer to each other, since the air is moving so fast that the coolant temp plays much less of a factor in what the MAT sensor is reporting to the ECM.

So if you think about it, in your situation... if the ECM is over-correcting for coolant temperature, it's going to unnecessarily lean out the A/F mixture. Then when the O2 sensor sees the result of that, it tells the ECM it's not putting in enough fuel, so the ECM adds the fuel, but it raises the BLMs in the process. This seems like it explains your BLM history table where the BLMs are high, but at only lower-mid engine load/speed. At the higher airflows, the BLMs start to come back in line because the Inv MAT Table is telling the ECM to not pay so much attention to the coolant temp.

BTW, You may also need to do some re-tuning on the VE table after making this change.

 

Was the exhaust leak ahead of the O2 sensor or after it? Not familiar with Vettes, but my guess is its up on the exhaust manifold? Depending on how big the leak is, it may or may not be able to fully explain a 160 BLM...

I still think you should be re-tuning for your MAT sensor relocation though.

 

That is very interesting. The MAT relocation was done before I bought the car, I never even thought about it. I had no idea the ECM did that. When I get the chance, I will alter those in my bin, as well as the injector offsets.

 

It was ahead. Like you guessed, its right on top. It's fairly large, but I also don't know if its enough to be causing the problem. I can feel it pulling a vacuum but its not very strong. I also have no idea how this changes with RPM. (my car is loud, its late, and there are many neighbors, so I don't want to rev it right now).
I will absolutely do the tuning as well. Like I said before, I'm not sure how much I'll be able to get done throughout the week, so it may take a little while before I can get everything fixed and get another log.