Hello! This forum comes highly recommended for TBI tech. I have a 1991 K1500 with a 4.3, at the moment. I've been used to 19-20mpg and lately it's been pulling down 15 if I'm lucky. Throttle has a dead spot when accelerating from a stop or slow roll. Compression is good. Leakdown test showed nothing out of the ordinary. I've done the "ultimate" TBI mod, spacer, 3 wire o2 upgrade, AFPR set to 14psi, cat delete, ram air, and one-in-two-out dual exhaust.

I've replaced the CTS. It seemed to quiet the droning exhaust noise in the cab, but did not help mileage. Next was the cap, rotor, wires, and plugs. That helped... but it's not near where it used to be.

Base timing was 0* TDC. Tried advancing base timing 4*... it pings. 2* advance it pings. Now when I put it back to 0* it STILL pings, but slightly.

So it's pinging lightly, hesitating, and smells like it's running rich... Although the plugs tell me the fuel mix is good... Go figure. The o2 sensor is Bosch with 20k miles. Hesitation could be a bad TPS or too much fuel. Over-rich fuel mix could be o2 or MAP. Pinging could be MAP, TPS, etc. I'm at a loss.

Any help is appreciated before I blindly invest in a handful of new sensors.

 

Probably running rich but why and where. I would do some datalogs to see what is going one, this should work also for your application http://dynamicefi.com/.

 

Lean condition will also cause hesitation. When you installed the 3wire(heated) O2 sensor, did you change the sensor ground location? Definitely sweep test the TPS. You can use a cheap analog volt meter for this. It should move smoothly from .5 to 5 volts as the throttle is opened with no glitches or drop outs. Also, check inlet air temp sensor as it also affects AFR.

 

I haven't got a datalog setup. I was planning on getting involved in it once I built the V8 to replace the 4.3... maybe I'm wrong but it seemed a waste to dump that kind of technology into a V6.

There was no sensor ground (other than being threaded into the exhaust) with the one wire sensor. When I switched to the 3 wire, I grounded it on the transmission case.

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I've heard people doing this. Since it needs input energy to create signal voltage, where in the harness pigtail should I put the probes so I don't ruin anything?

I don't believe my engine uses IAT; Only CTS

 

EBL flash works the same for V6 or V8, for V6 you just use one of the V6 calibration that are included.

The day you slap in the V8 you use one of the V8 calibrations, and good thing is you will already know how to tune it.








edit: sounded like EBL and the ALDL cable are related.

Or maybe this could work for dataloggin your application with only a ALDL cable and laptop http://winaldl.joby.se/

 

Reviewing diagrams for your engine, it appears you're right about the IAT. To sweep test the TPS, you want to back probe between the signal circuit and the sensor ground. Best place is right at the sensor. I generally use Fluke back probes. They are fine stiff wire probes that can be carefully inserted beween the wire insulation and the weatherpack seal at the back of the connector. I finely grind the tip at a sharp angle to ease insertion. Turn on the key and youll know when you have them inserted correctly by the voltage reading. Another method is to make jumpers using GM weather pack terminals and 3 lengths of wire. In fact this is how we learned to do it at GM tech school. You can buy the GM terminals at NAPA.

Your O2 is grounded through the ECM. The ECM has a specific O2 sensor ground. Its a tan wire and is probably attached to the rear of the pass side head. You may want to check it.

Datalogging is invaluable in diagnosing EFI systems. Any scanner compatible with GM OBDI will work to monitor ECM data. This data will most often reveal the cause of your issue. The EBL and What's Up display from Dynamic EFI is a great system and a bargain for the price. Because your existing ECM can be recalibrated to work with a variety of applications, you're really not wasting money to invest in this system now.

 

How is the spray pattern of your fuel injectors? You can see this with the air cleaner removed, and the engine running. It should look like a cone, it should be fanned out, and not a stream. If they are clogged, it can make your truck run like crap and drink fuel. I changed them on my 89 c1500 350, with the ultimate TBI mods, and went from 13 mpg to 21 on the highway, and about 18 average.

 

Sounds good. I'll post findings tomorrow

Ok, silly question: My truck came with a single wire O2 which grounded itself on the exhaust. The ground I'm speaking of is for the sensor heater to work. How did my single wire sensor ever work if it needed to be grounded onto the ECM ground attached to the head?

I was under the impression that usng a laptop wasn't the same as chipping adjusts ecm banks. Once thomas1976 posted the link I started looking at what I needed to get started. Any recommendations on a place that sells ALDL cables that aren't highway robbery?


That was what drove me to mod the TBI when I had. After noticing the spray pattern on the left-side injector looking like crap, I did everything at one time.

 

Keep in mind you will no longer need the ALDL cable once you upgrade to EBL.

 

EBL?

 

EBL is a piggyback add on to your ECM offered by Dynamic EFI. It runs about $450, IIRC, and allows reprogramming for various engine configurations through a PC interface. It also works with Dynamic's "Whats Up" display which is a very detailed and complete data viewing and recording program. Its a real cool setup. Check it out on their website through the above link.

The O2 ground Im referring to is from the ECM to the rear of the pass side cyl head. It is a dedicated ground for the ECM's O2 circuit. It is not part of the sensor wiring itself. I simply recommended you check it because it's a common cause of inaccurate O2 sensor readings. I'll warn you it's not easy to get at. You need a mirror to see it.

 

http://dynamicefi.com/

 

Your symptoms would indicate that EGR function needs to be checked.

For basic drive-ability and maintenance issues there are several excellent, certified mechanics more familiar with your rig available here,

http://www.chevytalk.org/fusionbb/sh..._Chevy_Trucks/

and here,

http://www.fullsizechevy.com/forum/g...l-maintenance/

this type question would be answered on those forums.

If you are interested in DIY tuning please read through ALL pertinent stickies, then ask questions.

 

EGR will affect idle quality first and foremost. So far I dont see anything in the OP's description of symptoms that points to EGR.

Sorry I missed this before: You say your injector spray pattern was inconsistent from one side to the other? Sounds like you need to have your injectors serviced. Remove them from the TB and take them to an injector service shop where they perform sonic cleaning.

There are different methods of datalogging. In my work I use a scan tool to monitor data. These tools can also record "movies" of ECM datastream if desired. One inexpensive and very effective way of accessing data is to purchase an early model scan tool. The GM Tech 1 was the factory tool for these cars. These tools are available cheap online. However, they haven't been made for several years and are sometimes hard to find. Another option is the Sanp On MT2500. I keep one of these in the bottom drawer of my cabinet for when older vehicles come in. Its bulletproof and works well on factory 3rd gens. You can find them for about $300. You can also purchase ALDL interface and datalogging software for your laptop but it can be pricey and if you think you might consider going with the EBL setup, the ALDL interface would be unnecessary since the EBL acts as an interface.

 

Inoperative EGR = pinging & poor fuel mileage.

EGR stuck open = poor idle.

 

EGR inop does not cause poor fuel mileage. It can cause pinging by causing high cylinder head temps. This is more likely to occur in hot weather.

The primary purpose of exaust gas recirculation is to reduce or prevent the production of oxides of nitrogen. It does this by reducing combustion temperatures which it does by injecting a small amount of inert gas(exhaust is almost pure CO2) into the intake stream. Lean mixture engines rely on this reduction of combustion temps to prevent cylinder overheating.

 

My injectors spray fine. The TBI has been rebuilt. I said that earlier.

 

Of course. I get that now.

 

So I'm thinking that knock sensor counts, ESC operation & the connections of both need to also be checked.

 

How is the vacuum line to your MAP sensor? Check it for leaks or restriction. Check your EGR valve. Even though i dont think its the cause of your problem, I dont know everything. Find a way to monitor data. Look at integrator and block learn. they will probably point to a fuel control issue. look carefully for any vacuum leaks.

I like the look of the EBL setup for datalogging and if you are thinking of stepping up to a V8 in the future, it may be perfect for you. Old scanners are old technology and generally bulky and slow. The EBL lets you use your new laptop as an interface.

 

Will post findings in a few days. Work is throwing alot of OT around and I'm taking it while it's available.

 

Been a few long days. To update: In january, I replaced the Bosch o2 with a new Denso, switched out the Map with a new part, and readvanced the timing 2*. Pinging is gone.

 

Make sure you have a good 195* t stat, a cooler running engine (160-180*) will have poor mpg then a hot running one (190-200*).

 

unless some tuning is involved.