Chevy/GM TBI expert advise needed

Ugh. Over the weekend, while waiting for the fuel regulator diaphragm to arrive, I thought I’d try to run the engine again. I got absolutely no combustion whatsoever, … and nothing but a couple of drops from the injectors. The last time it acted like that was when the fuel pump went bad. I pulled the in-line fuel filter on the off chance it had plugged. Nope, I was able to blow right through it. Asked my wife to turn the key while I watched the fuel line. The first time she turned the key a cranked for a few seconds, a fair amount of fuel came out, but when she went to do it again, there was a pump and then a dribble and then nothing. 3rd time she cranked, … just plain nothing.

It seems my brand new Bosch fuel pump has gone bad. Certainly the electrical connection is good or I would have seen no fuel come out. The only other thing I can think of is that maybe because the battery is kind of low on power, that it affected the fuel pump operation. That seems very unlikely though because the battery had enough power to crank the engine. Thoughts anyone ?

So I pulled the fuel tank from the G20 van again, while lying in the dirt. I used a floor jack on a big broken-down box to support the tank as it comes down. I expected it would be kind of heavy with about 4 gallons of fuel …, but guess what. Light as a feather (not really). The tank was essentially empty. I’d say, “duh, don’t overlook the obvious” except that I just can’t figure out where all the fuel went. Yes, the little bit it was running, it was running rich … but still …

Anyway I pulled out the fuel pump to examine the nylon sock. Somebody posted on the internet that fuel system cleaners added to the tank can dissolve the nylon sock, but it looked OK to me. So I put it all back together. I also put in the new fuel regulator diaphragm and cleaned the Idle air valve. I added 5 gallons of fuel, and expected everything to be perfect.

It started right up. It idled fast at first, not putting out a lot of smoke, looking closely I could see there was some black smoke. After it warmed the idle dropped down a lot, but still running ok and still putting out some (not a lot) black smoke. Then the check engine light came on so I shut off the engine and checked for the code. Again, it was the generic “too rich” code (4 flashes, then 5 flashes). I thought that the air cleaner being off might affect the way it was running so I put it back on. I cleared the code by disconnecting the battery. Again the van started right up and idled slowly, emitting a small amount of black smoke. Then I put my foot on the gas and let idle faster for a while. Again the check engine light came on. I shut it off and again it gave the same “too rich” code.

@TwinTurbo I can’t say for sure what effect replacing the temp sensor has had. While it’s running the best it’s run yet since mothballing the vehicle 5 years ago, I still have the “too rich” problem. Well, at least now I’m sure I can make it to the mechanic’s shop … presuming my tires don’t blow.

Thoughts from anyone on the lingering “too rich” problem ?

Well I replaced the coolant temperature sensor, and it wasn’t easy because a support bracket to the alternator was so close to the sensor that the socket wrench couldn’t fit between that bracket and the sensor.

I have a hard time remembering this but was it next to the thermostat housing? I want to be sure you replaced the right part (sender vs sensor).

yes, right next to the thermostat. The support bar that blocked using a socket on the the sensor I think was supporting the alternator or perhaps air-pump.

I would be checking the EGR valve to make sure it’s closing. If it’s not, there will be a loss of vacuum for the MAP sensor which will cause it to run rich. A leaking intake manifold gasket will also cause a rich condition. And also check the passage on the throttle body for the MAP vacuum. This can cause the vacuum to MAP sensor to be low which will cause a rich condition.

Thank you Pete. Could you please explain how to “check the passage”. There is a hard plastic tube, with what sort of looks like an electrical connector but I think it’s actually a vacuum line. This runs from right between where the in & out fuel lines meet the throttle body and to the map sensor. An EGR system problem should flash a code which I have not gotten, but if it’s like TwinTurbo said about the temp sensor, codes don’t always flash when they should. Since it was running properly many moons ago it has never over-heated or froze from cold which might cause a manifold leak. … just searching for the highest probabilities.

I’m just wondering about the rebuilt injectors I put in. Though I see a definite conical pattern to the spray, I think (but am not sure) I see drops coming down the center of the cone as well. In the regulator housing, the pressure which is put on the spring can be changed by screwing in or out a bolt which will move up or down the doo-dad which contacts the bottom of the spring as it sits in operation. However access to this bolt can only be had by un-soldering a blob of solder at the bottom of the regulator housing. Although the injector re-manufacturer says these injectors are for my van, a lot of people install an adjustable regulator unit, allowing access to that bolt. Right now the soldered “default” setting has the doo-dad in quite a low position as it sits in operation (less pressure on the spring), thus lower pressure on the fuel flow, thus lower fuel pressure. Fatigue of the spring would cause lower fuel pressure yet. Perhaps not all the fuel is getting adequately atomized. I am not a mechanic and do not know if what I’ve said makes any sense.

It will only flash an EGR code if it has ran long enough to test the EGR flow which it uses the oxygen sensor for. And from what I can gather here, it hasn’t been driven long enough to know. The oxygen sensor on this vehicle is a single wire which takes forever to get “lit up”. This is not an OBD II system so there’s no EGR position sensor. I am talking about the passage in the throttle body for the MAP. From what I understand, the throttle body has been removed to do what’s already been done, which to me means the Map sensor passage should already have been cleaned if it was gummed up. There’s not really any act of nature that’s gonna cause an intake gasket to fail. On GM’s it is verrrry common for an intake gasket to simply fail. I can’t begin to count how many intakes I have resealed on small block Chevys in the last 30 plus years because the gasket simply failed.

@pete peters, no I never took off the throttle body, so that passage would not have been cleaned. So many possibilities. So clueless on my part. Can someone describe how to use a cheap multi/meter to check the resistance (Ohms) of the injectors. I was told it can be done off the vehicle, but where’s the juice gonna come from? I don’t get it.

Latest happenings. @petepeters, I ran a pipe cleaner through the vacuum port on the TB which goes to the MAP sensor. The pipe cleaner was almost completely clean, including the front tip of it. I tested the resistance of the 2 rebuilt injectors that I bought as well as the 2 old injectors. They all read 1.3-1.4 ohms, so electrically all 4 are good. The outfit which sold me the rebuilt injectors has offered to swap them for injectors “with a lower fuel flow”. A nice offer, but they are not confident it will solve the “too rich” problem and neither am I. Thoughts about that from anyone? I’m thinking that I’d like to clean my old injectors but I don’t know how to go about doing it. These are chevy/gm TB injectors, not injectors into the cylinders via a fuel rail.
Any thoughts about how they might be cleaned? Thanks

Your injectors are faulty or fouled. Try a dose of seafome or techron, and cross your fingers. Otherwise 3m (sure I own stock in the company) makes a great injector cleaner.

What’s in the van now are the newly rebuilt ones, which is not to say they are assuredly good. These tbi injectors are rather different than most. Can I use seafoam in the same way as carb cleaner? How to avoid damaging the electronics?