89 C 3500 7.4l TBI with issues
 

We bought this beast (meant with affection) on the West coast and then moved up to the Rockies about 6 years ago. We now live at about 7,200 ft. We don't get to use it too much because this crew cab dually doesn't like much snow over about 1/2 inch.

Before moving out here we had a new engine put in and the rest of the truck 'worked over'. (still managed to break down 3 times on the way out here to Colorado - requiring a second engine and even a few trannies - but that's a whole separate story!) Since arriving here, the truck never seemed to run as strong as it did on the coast. It always seemed to idle rough when first started - even in the summer. Once warmed up, though, it seemed to do pretty good.

We ran into a problem this last weekend. We went to retrieve a load of lumber about 30 miles away. The beast ran real good all the way up but once the lumber was loaded he didn't want to start up again. After about 2 minutes with some finessing on the gas pedal, I was able to get it started but it was running real rough all the way back with an achievable top speed of about 55 on the straights. The check engine light would go on for a few minutes then off for a few then on , off and so on. We limped back home whereby I did a manual read of the check engine light warning codes (by shorting out pins 5 & 6 on the connector) and came back with a '44'. I believe that this means a lean O2 sensor.

Sorry about my ignorance...I know computers...don't know cars too well....

Does this mean I need a new O2 Sensor? Beyond that, is there anything else we should have done when coming up to this higher altitude? I questioned the mechanic whom put in the engine and was told that nothing special had to be done. Is that correct? Even though we live at 7,200 feet, I need to be able to use the truck to go over the passes which are mostly around 12,000 feet.

Thanks in advance for any help and suggestions...

Tom

Re: 89 C 3500 7.4l TBI with issues
 

ttt

Re: 89 C 3500 7.4l TBI with issues
 

Welcome to the board.

Code 44 means the ECM detects the engine is running to lean.

Being that it lacks power with a load, and runs rough, it could be to lean.

Replace the fuel filter.

If it still has a problem after the new fuel filter, then the fuel pressure needs to be tested.

The spec is 9 to 13 PSI with the engine running.

There is no fuel pressure test port.

Fittings need to be installed to test the fuel pressure with the engine running.

There are multiple failures that can causes the TBI trucks to have low fuel pressure other then the fuel pump. It is common for the fuel pressure regulator spring in the TBI unit to break and cause low fuel pressure. It is also common or for the hose that connects the fuel pump, to the sending unit, to leak and cause low pressure.

Re: 89 C 3500 7.4l TBI with issues
 

Does it have a cracked exhaust manifold?

Air can be drawn in exhaust leaks causing a false lean oxygen senor reading.

Re: 89 C 3500 7.4l TBI with issues
 

I had similar intermittent problems with my '92 K-3500 with a 454 and finally found the problem when the fuel pump completely stopped working at Buford, Wy.

We were towed into Laramie with our travel trailer tagging along late Friday afternoon. The next day they put a pressure gage at the fuel filter connection and found the pump was not putting out any pressure.

Saturday morning they dropped the tank, put in the new fuel pump and we were on our way after paying the $400 bill. We did get over-night camping in their parking lot for free.

Re: 89 C 3500 7.4l TBI with issues
 

I'm messing with the same issue. 1992 gmc 3500 7.4l. This engine is rebuilt bored 30 over stock cam it is running 229 degrees. Cant get it down. New water pump new fan clutch new radiator the water wont return into the expansion tank. I reset timing to factory setting after unplugging set timing wire. I pulled intake and heads gaskets looked good was running lean and found vacuum line going to egr valve broken. I'm about to pull my hair out with this thing.

Re: 89 C 3500 7.4l TBI with issues
 

Welcome to the board!

Are you getting the 229 degree reading from the temp gauge or from the ECM data?

Did you set the timing to Zero or 4 degrees BTDC?

Does your truck have a canister purge valve? I have run across several 1 ton trucks leaking vacuum at the canister purge valve.

Re: 89 C 3500 7.4l TBI with issues
 

I set the timing at 4btdc I recently reset the heads and the temp is coming from the guage but the water temp when I place am overflow funnel in the radiator never runs above the thermostat. I have a new manual guage in the left head. I noticed that it has a a 5 blade fan amd everything I've seen recommends a 6 blade fan. The purge canister isn't used the vacuum line is disconnected and plugged going to it.

Re: 89 C 3500 7.4l TBI with issues
 

The canister is disconnected and vac line is plugged. I set the timing a 4btdc. I finally got it cranked yesterday. The temp is coming from the guage 8n the left head. I mounted a new manual guage. I noticed when I took the motor down that the heads and pistols had a white haze on them like it. Was running lean. I repaired the egr lines. The injector flow looked good I haven't checked fuel pressure. I noticed every parts store calls for a 6 blade fan and this truck has a 5 blade fan on it. When that guage goes up I engage the electric fan manually and it doesn't make a difference

Re: 89 C 3500 7.4l TBI with issues
 

Gm dash gauges are not quality instruments.
I would look at the ECM data to see what temp it shows.
You could also look at the temp with a infrared thermometer right by the thermostat housing.

You should test the fuel pressure while it is being driven. The fuel pressure regulator and the connection hose in the tank are common causes of low pressure other then the pump.

If the electric fan is not making a difference, I would not worry about how many blades there are on the fan right now.

Re: 89 C 3500 7.4l TBI with issues
 

Boy, talk about a thread Hijack!


Back to the original OP. Sounds like you may have a vacuum leak in the system. Most common is the gasket underneath the TBI or the TBI adapter. With the engine running, spray some carb cleaner around the base of both and see if the idle changes. Also check the vacuum line to the MAP sensor. Actually check all the lines for deterioration or cracking

Re: 89 C 3500 7.4l TBI with issues
 

I wouldn't say it much of a hijack. Idk how to post new threads and the last one posted on here was 2011.

Re: 89 C 3500 7.4l TBI with issues
 

The original person that started the thread only made one post, over 6 years ago, so I don't think of this as a hijack.

To start a new thread you click on the box named "New thread" at the bottom left corner of the page of current threads. Being you posted here, you may as well keep going here because nobody else is using the thread, so you are not interrupting anything.

Welcome to the board!

Re: 89 C 3500 7.4l TBI with issues
 

Chevytech helped me with a problem a good while back and after a lot of head scratching and testing I never could find anything wrong.

I finally discovered a lot of my problems were caused by a faulty fuel injector. I was watching the spray from the injectors when I realized that one was spraying a lot more fuel than the other. Replaced them and that fixed my lean condition.

Re: 89 C 3500 7.4l TBI with issues
 

I hit 250 today. New fan clutch new radiator new waterpump. I ain't sure but I think they gave the wrong rotation. I specified ccw and they said yes ccw is standard but it ain't. Standard is cw I believe. I just need to be able to use this truck. I pulled the codes nothing for lean at all.

Re: 89 C 3500 7.4l TBI with issues
 

I would not be surprised at all if they sold you the wrong water pump.

Re: 89 C 3500 7.4l TBI with issues
 

What is a normal temp for this truck znd. Most importantly my fuel pressure is really low my injectors are pulsing not spraying. How much hotter would this cause my truck to run.

Re: 89 C 3500 7.4l TBI with issues
 

On a 1992 TBI big block the fuel pressure spec is 9 to 13 PSI. When the system is in good condition they do not run at the low end of the spec.

If the fuel pressure is low it will be running lean at least at times.

A lean mixture burns hotter. Much hotter. It can burn a hole through a piston.

I would expect to see a coolant temp of 195 to 220 degrees with some load.