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Old 03-25-2011, 11:21 AM   #1
irongun324
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1988 350 TBI idles funny, stalls when put in gear, and accels rough...

So for the questions:

1) Service engine light didn't come on until after 5-10 mins of driving (no faster than 45 mph). Without reading codes yet, any gut suggestions (perhaps better answered in conjunction with #2...)

2) It won't accelerate smoothly. It will start out SLOW and smooth until about 15-20 mph, then it wont accelerate worth a flip for a few seconds (no change in pedal pressure) before acting like it starts "catching" and resumes accelerating. Very consistent doing this, so essentially I can't take off at all.

3) It had a tendency to stall when I first test drove it, easily overcome with very slight pedal pressure when at a stand still. I made it home a 15 min drive without stalling this way. Could be related to #2?

It idles well enough it seems, but it's been sitting for almost 2 years, with being moved around the lot once a month or so during grass cutting season. Hoping bad fuel might be part of the problem, i put 18.5 fresh gallons in it with a bottle of the Techron fuel system cleaner right as I started the drive home. I didn't let it just sit at a light in gear, not wanting to risk it stalling in the middle of the road so im not sure if it made any difference on the way home.

I'll stop there, as those are my primary concerns right now (getting it running well). Thanks for looking.

I intend on new plugs/wires at a minimum today, and checking the timing. If it doesn't clean up, what about fuel filter and EGR valve?

-Trey
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Old 03-25-2011, 01:24 PM   #2
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

The engine may smooth out as you drive it some, but I would also change the oxygen sensor.

Auto Zone and O'Riellys will run a code check for you. Sometimes it depends on which O'Rielly's guy you talk to because the one I worked at had a policy not to run codes just to loan the code reader. Usually if you went there after 6:00 pm we would run the code.
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Old 03-25-2011, 03:56 PM   #3
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

My guess would be oxygen sensor or fuel filter. I had a bad egr valve and my symptoms were normal idle, off idle acceleration would lope really bad almost like blower surge and it would go away as it accelerated and if you let off it would make a weird sound then go back to normal idle. I found out it was the egr by unplugging the egr connection completeley, its on the passenger side of the intake manifold possibly touching the valvecover about in the middle, unplug it and if it runs normal its your egr but i suspect o2 sensor or fuel filter. good luck
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Old 03-25-2011, 07:19 PM   #4
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

Check fuel pressure - if you have original fuel pump the chances are that either FP is tired or fuel hose between FP outlet and feed through is leaking.

Codes can be read by inserting a jumper between pins A&B of ALDL and reading the number of blinks of SES light. Insert jumper, turn ignition on, without starting engine.

//RF
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Old 03-25-2011, 08:27 PM   #5
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

I checked the code: 44 was the only one, Lean exhaust right?

I went and grabbed some plugs/wires as a good start, and went ahead and got a new fuel filter. I figure that can't hurt after sitting for that period of time.

I'll go from there... updates soon.
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Old 03-26-2011, 12:37 AM   #6
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

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I checked the code: 44 was the only one, Lean exhaust right?

I went and grabbed some plugs/wires as a good start, and went ahead and got a new fuel filter. I figure that can't hurt after sitting for that period of time.

I'll go from there... updates soon.
8 time out of ten code 44 is due to low fuel pressure or if one of the two injectors not firing. Injector firing can be easily verified. Low fuel pressure can be due to weak fuel pump or burst in a fuel hose (inside the gas tank) Another common culprit is old fuel pressure regulator diaphragm and weak or broken fuel pressure regulator spring.

//RF
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Old 03-26-2011, 10:21 PM   #7
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

Well it "seems" better, as far as idling goes. Definitely still no throttle response though. Even just trying to rev the engine in park, it's not smooth.

Any suggestions on ways to test other things: diaphram, spring, or just fuel pump altogether?

I'm assuming I have to drop the fuel take to get to the pump? I see no access panel inside the back.
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Old 03-26-2011, 10:46 PM   #8
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

did you try to unplug the egr?
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Old 03-27-2011, 01:34 AM   #9
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

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Originally Posted by irongun324 View Post
Well it "seems" better, as far as idling goes. Definitely still no throttle response though. Even just trying to rev the engine in park, it's not smooth.

Any suggestions on ways to test other things: diaphram, spring, or just fuel pump altogether?

I'm assuming I have to drop the fuel take to get to the pump? I see no access panel inside the back.
Before dropping gas tank for fuel pump replacement I would check fuel pressure. This can be done by removing fuel filter and inserting a test T with a fuel pressure gauge. Based on your symptoms I am going to venture and say that you are running 5- 6 psi. With engine idling, take a look at a fuel spray coming from injectors. If it looks like it contains large droplets then it is indicative of a low fuel pressure. With normal fuel pressure (9 to 13 pSI) there should be no large drops - a fine fuel mist should be hitting bore side walls.

//RF
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Old 03-27-2011, 09:55 AM   #10
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

How do I look at said spray? Air filter off and shine a light down? I'm familiar with trucks in general, but haven't actually done a lot of things.
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Old 03-27-2011, 10:02 AM   #11
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

Just remove the air filter. The two injectors are gonna be hanging right there in the middle of the throttle body bores. You should see a fine mist. If they are dripping or slowly leaking your looking in the right area.
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Old 03-27-2011, 04:52 PM   #12
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

Ok Update.

The injectors are "misting" I'm not sure I would call it a fine mist, but maybe it is. Either way, bought the regulator rebuild kit from Autozone, with new diaphram and spring, and gaskets. Put this together and it has improved, but still not fluid, even wants to die going in reverse very slowly just a short distance.

I've heard harbor freight has an inexpensive fuel pressure gauge, reads up to 15psi. Any experience with one of these?

As for the EGR valve...

http://67-72chevytrucks.com/gallery/...0/P1040992.JPG

You can see 2 ports on the left, one on the right (What exactly is this part?). The right goes to the TB, left (at least the one that's connected) to the EGR Valve. I have zero vacuum on egr side, but I am getting good vacuum to the throttle body.

Here is the overall look.

http://67-72chevytrucks.com/gallery/...0/P1040993.JPG

Also it seems to Rev fine in park. Seems peppy, feel it torqueing a bit.
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Old 03-27-2011, 05:36 PM   #13
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

Quote:
Originally Posted by irongun324 View Post
Ok Update.


As for the EGR valve...

http://67-72chevytrucks.com/gallery/...0/P1040992.JPG

You can see 2 ports on the left, one on the right (What exactly is this part?). The right goes to the TB, left (at least the one that's connected) to the EGR Valve. I have zero vacuum on egr side, but I am getting good vacuum to the throttle body.

Here is the overall look.

http://67-72chevytrucks.com/gallery/...0/P1040993.JPG
That is what is known as EGR vacuum solenoid (there are other names) - it is controlled by ECM. ECM pulse width modulates (PWM) ON-OFF amount of vacuum applied to EGR valve. When this valve is OFF the EGR connected side is vented to atmosphere (so that vacuum is removed from EGR valve diaphragm). In normal operation this valve is vibrating - ON -OFF determines how much vacuum is being applied to EGR valve. Expensive to replace when they go bad.

//RF
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Old 03-27-2011, 05:41 PM   #14
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

Should I have zero vacuum on the EGR side?

Other things to look at? Would rather troubleshoot than throw parts at it...

EDIT: I plugged the vacuum line going to the TB from the EGR solenoid, didn't help any. I guess my EGR valve isn't my main culprit. Still haven't had a chance to test fuel pressure. Autozone says they dont rent the tester anymore, but they sell a 45$ model, that has a GM TBI adaptor. Wonder if its worth it.
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Old 04-01-2011, 04:40 PM   #15
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

Alright update. So I noticed that my muffler is completely shot, falling apart... would that relate to any of this? Just curious...

I checked vacuum lines, and the ones going to the MAP, EGR, and AIR all look fine. The one going to the canister, and others in that route were pretty rough looking so i've replaced those now. After a quick test drive, not any noticeable improvement.

Now that it's warmed up, checked again for any vacuum leaks (while running), cant find any. Could it take a long time for the computer to realize the problem is gone and relearn to run smoothly? Seems to be idling much better right now...
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Old 04-01-2011, 05:23 PM   #16
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

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Originally Posted by irongun324 View Post
Alright update. So I noticed that my muffler is completely shot, falling apart... would that relate to any of this? Just curious...

I checked vacuum lines, and the ones going to the MAP, EGR, and AIR all look fine. The one going to the canister, and others in that route were pretty rough looking so i've replaced those now. After a quick test drive, not any noticeable improvement.

Now that it's warmed up, checked again for any vacuum leaks (while running), cant find any. Could it take a long time for the computer to realize the problem is gone and relearn to run smoothly? Seems to be idling much better right now...
You can reset computer by disconnecting battery (engine is off) for about 30 seconds. This will reset all fuel trim levels

Another common cause of idle issues is a build up of carbon in the IAC passages. On high millage cars and trucks (TBI) carbon may prevent IAC panticle from closing of by-pass air passage resulting in hunting idle speed . Couple of shots of carb cleaner and a good brushing takes care of this pesky problem. Idle air inlet is at 11 o'clock position outside the left bore (near IAC motor).

//RF
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Old 04-01-2011, 10:15 PM   #17
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

I'll look at the IAC in the morning then, but here is some more info to digest.

After the vacuum lines today, i let it idle for 5-10 mins, made a quick around the block loop (hesitation still apparent). When I got back I let it idle a while longer still, 10-15 mins, and then realized it was idling a LOT smoother. No hunting, very smooth even idle. So I drove it again, farther this time, and there was almost no hesitation at all in forward gears. In reverse, going slow it still sounded like it wanted to stall (did once when I was turning around), but usually didn't. Drove it around for a while longer and maintained good enough acceleration that I didn't feel uncomfortable in traffic. When it was warm, I measured around 8.5 PSI on the return line side of the throttle body (disconnected wrong line, will check proper side tomorrow). Should I see the same PSI in this line that I would in the sending line?

After sitting for 30-45 mins and cooling down, it was back to poor/hesitating acceleration again, and slight hunting in the idle. Thoughts?

Also, was thinking of trying to bypass the EGR solenoid, and hook the EGR valve straight to the TB vacuum inlet. Good idea? Would it prove anything if it helped when the engine was cold?

Also bought and O2 sensor. I'm guessing the one there is old judging by other parts, and wouldn't hurt to be replaced.
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Old 04-02-2011, 09:34 PM   #18
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

Well now that I finally could test fuel pressure.... Im getting less than 8 psi at the throttle body. So bad pump? Or could it be grounds?
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Old 04-03-2011, 10:07 AM   #19
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

Quote:
Originally Posted by rfmaster View Post
8 time out of ten code 44 is due to low fuel pressure or if one of the two injectors not firing. Injector firing can be easily verified. Low fuel pressure can be due to weak fuel pump or burst in a fuel hose (inside the gas tank) Another common culprit is old fuel pressure regulator diaphragm and weak or broken fuel pressure regulator spring.

//RF
I guess I'm back to this post. I can go ahead and remove the tank and see how things look inside, problem is it's still 80% full! As long as I disconnect the wires and fuel filler neck, it can be lowered (via floor jack) without issues right?

Besides obvious damage (hose/filter inside the tank being shot), what else can I do?


On another note, could it be that the engine warming up is warming up the ignition coil also? Kind of a random though this morning
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Old 04-03-2011, 12:42 PM   #20
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

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Well now that I finally could test fuel pressure.... Im getting less than 8 psi at the throttle body. So bad pump? Or could it be grounds?
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IRC you have replaced FPR diaphragm. The only other reason why FP might be low is a weak or broken FPR spring. If you had BOT putting TB together then spring is probably OK. 8 PSI is barely enough to idle engine - I run my fixed FPR TB's between 15 and 18 PSI (with adjustments in EPROM). Increased FP improves fuel atomization.

1) Bad or tired pump (after 20+ years in service it is done).
2) Burst in the fuel hose between pump outlet port and tank sending unit.
3) Low voltage at the fuel pump terminals. (Should be around 12.5+ Vdc with engine running at the tank terminals)

Most of the time it is 1 & 2 with #2 causing #1. When you get a replacement pump make sure to replace the hose with SAE30R10 - fuel submersible rated fuel line. Do not use commonly available 30R7 or 30R9. Most pumps kits come with fuel hose supplied - it should be the correct type. If you pump kit is missing this hose you can get it from Napa - 3/8" ID part number H213 (Gates 42196184). Kragen and Autozone do not carry, unless special order.

//RF
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Old 04-03-2011, 01:49 PM   #21
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

I rebuilt the FPR with the Autozone kit, which included a new spring and used the new spring. Either way this is without taking the FPR into account, I was measuring at the inlet, fuel line disconnected and plugged into a pressure gauge (dont have the materials to make an inline one yet).

Autozone has a fuel pump rebuild kit, that doesn't include strainer for 54, or I could order THIS from Rockauto. Thoughts? I don't really have the budget to spend 150$ on a new whole assembly, especially if I don't need to. The gas gauge seems to be working fine for example. I'm just looking to keep it ticking, for occasional use as a work truck.
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Dad's: 68 C10 Stepside (work truck condition, runs though)
59 Apache Fleetside (rusted pile of metal - hopefully soon to be father/son project when he cleans out his garage!)

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Old 04-03-2011, 03:27 PM   #22
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

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I rebuilt the FPR with the Autozone kit, which included a new spring and used the new spring. Either way this is without taking the FPR into account, I was measuring at the inlet, fuel line disconnected and plugged into a pressure gauge (dont have the materials to make an inline one yet).

Autozone has a fuel pump rebuild kit, that doesn't include strainer for 54, or I could order THIS from Rockauto. Thoughts? I don't really have the budget to spend 150$ on a new whole assembly, especially if I don't need to. The gas gauge seems to be working fine for example. I'm just looking to keep it ticking, for occasional use as a work truck.

OK - you have performed a dead head pump test - a good TBI pump should deliver 20+ PSI. You have a bad fuel pump partner!

Rock auto kit is a good replacement kit and has the right hose included. Inlet strainer should be replaced as they get clogged over time (time is our enemy!). Please note since we live in CA our fuel (oxygenated, skunky smelling poop) and contains 10 to 15% ethanol (depending on refinery). This stuff is bad news for older vehicles - anything designed and built before 1995 or their about. You should thank Air resources board for this one.

//RF

//RF
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1975 Chevrolet C20 longbed
350/700R4! with 3inch body lift
Dual Flowmasters Super 40's!
TBI retrofit completed (2007-07-29)
New 383CID (+030) 08-304-8 9.5:1CR x36,005 (2012-12-17)
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Old 04-03-2011, 04:40 PM   #23
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

Ours is usually 10% here in Alabama. I heard there is a anti-ethanol additive for older vehicles, any suggestions?
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Old 05-08-2011, 11:33 PM   #24
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

Fixed!

After rebuilding the fuel pressure regulator, new fuel filter, plugs and wires, I finally dropped a new fuel pump in and seems to be running like a champ.
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Old 05-10-2011, 07:39 PM   #25
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Re: 1988 350 TBI idles funny, stalls when put in gear, and accels rough...

You might have a bad MAP sensor. It is cheap and it is THE main sensor the controls the fuel mixture off idle.
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