Baffling 1988 Chevy 1500 w/305 fi

[Cptace61]

Hi. I am new to this forum but I am totally at wits end. I bought a 1 owner 1988 Chevy Cheyenne 2 wd with a 305 tbi . Has 130000 miles and been not used much. Ran like crap getting it home as expected. Ran some carb cleaner and super through it and improved a bunch. Ok, here's the symptoms. The truck falls on its face, skips and sometimes fires through the carb. and throws a code 44 (lean exhaust). In higher rpms it surges.
Ok, here's what I have done.
1) Cat was plugged up. Replaced it.
2) Replaced cap and rotor. Spark plug wired new.
3) Replaced fuel filter.
4) Checked fuel pressure ( 9 psi pretty steady loaded unloaded)
5) Removed and tested module in distributor. Was bad so I replaced the whole distributor.
6)Replaced the MAP sensor.
7)Replaced the knock sensor and check the wire for a signal and grounding. Good.
8) Replaced the ESC module.
9) Checked for vacuum leak.
10) Checked engine timing. Also had timing checked with ECM bypassed. Would rev engine during timing check and we would see the timing advance to a point then retard itself.
11) Checked and tested Idle Control Valve. No problem.
12) Checked EGR. No problem.
13) BTW replaced spark plugs.
14) Reground the engine to the firewall and grounded the ECM box.
15) Replaced ignition switch.
16) Replaced the water temp. sensor.
17) Replaced the ECM.
Ok, after all that, still nothing made a difference. If anything, slightly worse.
Now for the kicker that I came across accidently. I was turning off the truck and then decided not to before it shut off. In other words I did turn it off for a half of a second and turned it back on while it was still spinning. Ran great till the next time I shut it down. So I tried starting it, quickly flipping it to off then run before it shuts off and runs fine. Go Figure. I am open to any good suggestions as I have my mechanic and parts folks baffled.
Thanks.

[IADC43]

Is the computer brain box original, maybe been changed, or checked for faulty operation?

[Kudzupatch]

Clogged/dirty fuel injectors? The ignition switch trick doesn't make sense but otherwise sounds like it is running lean. Your mechanic should be able to drive it watch the mixture and see if it is running lean.

Also, as Chevytech has pointed out before, replacement parts are often worse than what is on the car to start with. Throwing parts at the car as you have may have introduced new problems. I have had 2 (new) bad distributors caps in 3 months.

[Cptace61]

The original ecm was in it and the new one is an exact match. Has same syptoms with both. The fuel injectors have been check and are spraying nicely. Al parts used are oem. Thanks.

[YankeeHauler]

Sure it's not bad gas?

[Cptace61]

I have put close to 2500 miles on it.. Not the gas. Besides, when I "reset" it runs like a champ. That's why I am here.

[ChevyTech]

As already mentioned, replacement part quality is so bad now, that you may have added several problems by replacing so many parts.

If you still have the old parts, don't discard them, you may be putting them back on the vehicle. Most importantly the ECM, EGR, and spark module.

You did not mention what brand of parts, or where the parts came from.

The, turning the key off, and back on, is a trick I used to use on Fords. I is most likely helping because it is putting the system back in open loop.

Does this truck run well when cold?

Have you tried driving it with the oxygen sensor unplugged?

Does this truck have A I R (Air Injection Reaction) aka smog pump?

I see no oxygen sensor on the parts list. Did you replace that? If so I hope you did not use a Bosch sensor.

Have you cleared the code 44 from the memory and see how long it takes to get set again?

[Cptace61]

I am sorry. I have put these parts on over a period of time. I have made sure I replaced the parts with oem stuff. I have tested and retested most of the work I have done by swapping said parts out from a good running 1988 chevy 1500 tbi 305 they have at the shop. The parts I have replaced I chose to keep because they are new and not 17 years old. Hence the word baffling. No the truck doesn't have a smog pump. As for the oxygen sensor, no I haven't checked that and the truck doesn't run well cold. You are the first to bring up the O sensor and I will look into that. Thank you and I will keep you posted. I will have the code cleared and see how long b4 it shows up again.

[ChevyTech]

If the truck does not run well cold, we can't blame the oxygen sensor.
The oxygen sensor does not affect the fuel mixture on cold start-up when the system is running in “Open Loop”.

This does not mean the oxygen sensor is good, it just means it should not affect the way it runs on a cold start.

You may want to test the fuel pressure again.
TBI fuel pressure should be constant without fluctuation.
The pressure regulator does not vary the pressure due to engine load (vacuum changes), like other systems.
The fuel pressure is usually not at the bottom end of the specification if everything is in good condition. It may just be the gauge you tested it with.

If you restrict flow on the return line, the pressure with a good strong pump will increase to at least 18 PSI. This test should only be done for as short of period of time as possible.

The symptoms do sound like it could be running lean. Many people are finding that replacing the TBI injectors is fixing their lean running. My guess is that most of the injectors may be OK but the screens on the injectors are restricted. I have found there is a somewhat clear, milky slime in the fuel, in my area of the country, and it is plugging things up.

[Cptace61]

Ok, so there should be no fluctuation in the fuel pressure test at all? I was not aware of that. So what happens when I "reset' it while running? I guess what I am asking is shouldn't it go back to running like crap in a short time if the pressure is off? I will say from what I read it needs to be from 9 to 13 on this particular truck and it is on the low side with some flux, but I am first to admit I am not an expert by know means. I currently have the flu so I am slowed down to a crawl right now.

[ChevyTech]

The fuel pressure on this TBI system should be steady if all the parts are quality parts in good condition.

Spec is 9 to 13 PSI.

I have found pressure as low as 2 PSI and the only complaint the owner had was hard starting at times. Other owners will notice a difference if the pressure changes from 9PSI to 10.5 PSI.

Forcing the system back into open loop takes the oxygen sensor out of the equation.
When running in open loop the system is very dependent on the coolant temperature sensor reading and the MAP (Manifold absolute Pressure) and TPS, to calculate the fuel needed to run well. During this time other failures have little or no affect on how it runs.

If a vehicle will not run well in open loop ( before closed loop where the system take over control) then you should look at for mechanical problems, ignition problems, fuel supply problems, and the basic coolant temperature, MAP and TPS readings.

Don't over look basic problems thinking it has to be a computer problem.

Problems that have been very hard to find for people on the boards in the past are, a flat cam lobe, or head gasket failure between two cylinders, until the problem gets worse.

The popping back through the TBI you mentioned in your first post fits a flat cam lobe, failed head gasket between cylinders, bad TPS, or lack of fuel supply.

I want you to triple check the plug wires - firing order - to make sure you have not crossed any wires.

The code 44 fits a lack of fuel supply too.

I have found it is best to chase the code to its conclusion when someone does not know what the problem is.

[Cptace61]

I just want to be clear, when I turn off the ignition and turn it back on BEFORE the engine dies, am I going into open loop?. I am sorry but I seemed to miss that one. I totally agree with you, something is wrong in closed loop. I have checked the firing order several times, but I am always willing to recheck. As soon as I am over this flu I will be back at it with more info if possible.
1) clear code and ascertain how long before it codes again.
2) check firing order
3) double checked tfi"s for spraying. (not gumbed up)
4) For shts and grins going to check the o2 sensor.
5) The truck runs well in open loop as compared to closed loop.
Now, because I don't know and am not afraid to ask, is the fuel regulator control on the fuel pump or a separate device. It would explain to me why in closed the truck runs bad but in open it runs well. Is that a possibility?

[ChevyTech]

The fuel pressure regulator is in the TBI unit.

Here is a link to a photo of a broken regulator spring.
http://67-72chevytrucks.com/vboard/s...3&postcount=17

The post is from this thread.
http://67-72chevytrucks.com/vboard/s...d.php?t=347247


Turning the key off and on should be putting the system back into open loop until the timer expires like a restart. I have never tried doing that on Chevrolets. I unplug the oxygen sensor which keeps the system running in open loop.

[ChevyTech]

TBI illustration that shows the fuel pressure regulator.

http://www.snflupigus.com/Partspics/image054.jpg

TBI flow
http://www.hemmings.com/hcc/stories/...hmn_tips1.html

[speedygonzales]

Originally Posted by Cptace61

the truck doesn't run well cold.

Originally Posted by Cptace61

I totally agree with you, something is wrong in closed loop.

5) The truck runs well in open loop as compared to closed loop.
Now, because I don't know and am not afraid to ask, is the fuel regulator control on the fuel pump or a separate device. It would explain to me why in closed the truck runs bad but in open it runs well. Is that a possibility?

Fuel pressure is only controlled by the vacuum level applied to the FPR. It's a spring loaded diagram. Open or closed loop is not a factor on fuel pressure.

But what you are saying about open/closed loop AND cold does not make any sense. You should not assume when you do your switch off and back on trick that it's going into open loop. You should disconnect an O2 to see if it runs better since you know at that point it will be in open loop, no question.

My guess is it will not change anything. Further, I don't see where you did much with the injectors in the throttle body (not a carb) other than you used some carb cleaner and "super" WTH that is. The majority of repairs we do on small engines is cleaning restrictions in carbs. A film builds up inside the small passages and it can be very difficult to clean out.

With your code running lean, it would seem to indicate your fuel delivery system is restricted. To test the theory, find a way to restrict the return line to bring the pressure up higher and see if it runs better. You could then decide to clean the inside of the hard fuel lines and possibly replace the injectors. If that doesn't fix your issue, you may decide to up the pressure.

[Cptace61]

Ok, just a quick updated. Sorry so long but have been sick. Anyway, I replaced the fuel pump and problem solved. The rubber hose and gasket were destroyed by ethanol gas. Fell apart in my hands as I pulled it. Thank you all for your input.Was baffeling because I could reset and would appear to run fine. But anyway, thanks all.

[ChevyTech]

You’re welcome, and thank you for letting us know what fixed it.

As I said in post #9, the fuel pressure is usually not a the bottom end of the specification.

I am always suspicious of fuel supply problems when the pressure is at the low end of spec.