Ok, here is my story, I bought the truck about 6 weeks ago knowing that the previous engine had blown up. The truck was originally equipped with 5.7 and the rplacement engine is 5.7. Anyway the reason the guy sold the truck is the reason I am begging for help today. When I got the truck, it is a 4 speed, and you absolutely could not get it out of third gear, if you put it in fourth it would bog down and you would have to shift down accordingly. Anyway the guy swears the engine ran fine in the previous truck before the swap but has ran like this since the transplant.

On to the things that I have done----

Replaced O2 sensor
plugs
wires
ecm - 2 used - now have a new 1
iac valve - cleaned - 1 used - now have a new 1
esc - 1 used replacement
fuel filter
TPS - checked ok
map sensor - 2 used - now have 1 new
EGR valve - no effect unhooked -seems to be clean
coolant temp sens - checked ok
control module - new
injectors - changed in several with no effect - present injectors have good spray
TBI - rebuilt entire unit (including regulator)
Fuel pump - it has 2 (both checked between 14 & 14.5psi
Timing - Dead on at 0 degrees

Everything I have done to truck improves the way it runs but will not get rid of main problem - surging idle and falling on its face.

The last time I drove the truck was right after the tbi rebuild-- I started it up and immediately heard the surge knowing it wasnt fixed I reset the codes and went for a drive. After approximately 10 miles of it running absolutely flawless, I came home and told wife we needed to go for a long ride to make sure that it was fixed. Anyway, before we got completely out of the driveway, it was acting same as always- falling on its face - surging - code 44 cel. Though I have experienced many cel codes since owning including 33,34, & 44. Code 44 always seems to show itself every time??? There is one other thing I have not mentioned, the truck is hard to start for EFI - meaning it takes 5- 10 seconds of cranking before she fires (hot or cold)?? This thing is putting me in poverty and raising my blood pressure beyond its limits. Any help would greatly be appreciated. Thanks in advance!

One other thing I have noticed, that although the idle surge is almost always present, when driving down the road and it acts up - falls on its face an cel light comes on - you can shut it off and restart and it will run fine for approximately 2 minutes - presumably until reaching closed loop?

 

wow you people sure do come out of the wood work... dont you... but then again this is a K series forum.... oh wait a minute i am being told it is a 3rd gen forum...

 

Losing power under load in high gear. I could fill page after page of things to check. Start with fuel checking pressure under load. Pinched supply or return lines. Check timing and see if it's advancing under load. Are any brakes dragging or any other number of things could be wrong.

Saying injectors have good spray unless you have a proper way of inspecting them, just looking at them spraying tells you nothing. You tried several. Did you try some "new" ones?

Having to crank the engine for a few seconds before it starts sounds like the residual fuel pressure has dropped off. Is there a loose fitting and the system sucking air?

Codes 33 and 34 are MAF faults. The ECM doesn't know how much air is going into the engine. 44 is O2 lean fault. Engine isn't getting enough fuel.

 

Stephen

I think you mean MAP instead of MAF, but lets help this poor fellow since I doubt that he will get any decent help over on the other boards.

Code 33 MAP sensor signal voltage was too high (low vacuum) for 5 seconds
This code gets set when:
Engine is running
Throttle opening was under 4%.
MAP sensor output responds to engine vacuum. At idle MAP output should be between 1.0 to 1.5 Vdc. You can back probe Pin B of the MAP sensor with a DVM to measure this voltage directly.

Code 34 MAP sensor signal voltage was too low (high vacuum)
This code gets set when:
Engine speed is below 1200 RPM
MAP Sensor voltage is too low - less than 0.25 Vdc for less than one second
OR
Engine speed was above 1200 RPM
TPS was greater than 21%.
Since you have both MAP related codes popping up the question is where vacuum for MAP sensor is being taken from??? - Make sure that nothing else is connected to a vacuum line used for MAP. MAP line is connected to tap in the back of TB between the two fuel line outlets. Another source for MAP confusion is ignition misfire and cam overlap. If you have a 'bottom of page' cam you will have difficult time solving MAP codes without getting ALDL data to see what ECM sees. Also, check all engine electrical grounds.

Do you know what your idle vacuum is?
Do you know what cam was put into rebuilt engine???

I think once you solve MAP codes - Code 44 will go away since MAP controls main fueling.

Let us know what you find.

//RF

 

also, check the fuel pressure.
not just at idle or reving the motor, but while its acting up when your driving it.

 

It doesn't lose power at the high end it is actually worse on the low end<-- Especially taking off with a four speed --- Out on the road you can be driving 55 and it will just fall on its face-- you can still hold speed but a noticable 30% or more decrease in power <--- this can be resolved by accellerating through the slugishness as stated before it always runs good at wot <--

Just to clarify I used to have code 33 & 34 <-- these have been taken care of before the post, I think some misunderstood that I still get these occasionally!

The injectors I am using have been tested and are good and if there is a loose fitting somewhere in the system, I can't find it and I am sure I have had them all loose!

All grounds have been meticulously checked and have even added extras.

I do not know what my idle vacuum is, but I do know that it was checked and was good!

This is not a rebuilt engine--it is a stock transplant with stock cam

I do not have anyway to check fuel pressure under load -- but it is a truck with dual tanks and dual fuel pumps that check good at idle -- I find it hard to believe that both pumps would act this way under load or idle for that matter. That is when it acts the worst from idle to about 1800 rpm

I know the engine is not getting enough fuel - hence code 44 - I just cannot figure out why?

Just to make certain everyone knows -- these problems do not happen all of the time -- there are times when the truck runs - idles - and pulls flawless
But it happens more often than not.

As far as coming out of the woodwork <--- you would think that being a member of this sight, you would be proud to know that an outsider has chosen this form to ask a question pertaining to ones knowledge??

To others that have responded -- all of your thoughts are really appreciated.
I came to this board because with all of the studying I have done on this subject, this seemed to be forum that had some insight and that might be able to help me!

I am still open to any further diagnosis

 

Drop the tanks and see if there's anything in them such as a rag which can occasionally block the pickup.

As I mentioned in my original post, I could probably write pages of probable causes.

 

I know there are hundreds of causes - but do you think both tanks could have a rag in them? But seriously, I am just looking for something out of the ordinary that I haven't heard a dozen times or already tried that many! Something that makes sense that would cause it to act like this at diffirent times! By the way the rag would be a believable story if it only had one tank!

 

Hmmm

Need to do a bit more troubleshooting.

Questions?
1) How did you set timing - did you disconnect EST connector to set for 0 degrees??

2) Did you clear Code 42 after you set timing???

3) Do you get about 18 degrees of timing at idle once you reconnect set timing connector?

4) Do you know if you have a clogged up CAT???

5) Check fuel lines - kinks, pinched.

 

does the truck have cats? if so remove the exhaust and drive it, if it works ok, get new cats, if it doesnt have cats ignore this lol

 

Yes on EST

Yes on clearing the code

Somewhere between 15 and 19 hard to tell and remember

Dont know about the cat?? <-- it is original, but i really thought clogged cats effected high rpms rather than low rpms??

Fuel lines are neither kinke or pinched

 

Surging idle is indicative of a vacuum leak. IAC tries to keep engine from stalling compensates resulting in unstable idle. These are hard to find, but check the usual suspects.

6) If you have power brakes make sure that you do not have a leaky check valve between booster and intake manifold. Power brakes take off is usually near dizzy.
7) Check PVC and hose for leaks.

 

Your problem sounds exactly like the problem my Dad's truck had. His is an 87 GMC, 5.7, auto, dual tanks ect.
His problem? The fuel pressure regulator. I know in your first post you mentioned that yours had been rebuilt so it might be of no help to you to know this. The only reason I brought it up is because the symptoms are identical. There may be a small chance there is still a problem with it.

 

sounds to me like a fuel delivery issue. I know you said you checked fuel pressure but you might want to drive it with the fuel pressure gauge installed if you have the adapters to install it in line and check for any kind of drop. I would recheck that fuel pressure regulator in that throttle body especially if it was just rebuilt. Its a simple system. Also on those trucks if the tank were ever droped down someone may have replaced the very short sections of fuel line to the tanks with a longer one if this is the case its probably kinked and would show good pressure considering these trucks only have about 12 psi or so but wouldnt supply an adequete volume of fuel. Ive seen this a few times. The stock fuel hose that goes to the tank is hard to reinstall and just doenst seem long enough. other than that check and make sure your cat isnt restricted. wouldnt hurt to stick a vac gauge on this thing and check vac at idle and under load. restricted exhaust would show up on this test too. You have to perform these tests and take your measurements when shes acting up otherwise everythings going to read normal