Help 454 TBI

electrican · Dec 18, 2011

Got a 1989 454 TBI that when the temp outside is below 65 it will spit sputter and backfire and just act a complete idot until it warms up. I've replaced the ECM, COIL,Plugs, wires, cap, rotor button,temp sensor,TPS,IAC,checked fuel pressure,checked for vacum leaks. Even put a complete different throttle body on it.Even changed the o2 sensor. It don't throw a code and when it gets past 65 degrees engine temp it's fine. I'm at my wits end with this dam thing please help.

mmk5 · Dec 18, 2011

hey ran into this w/ a 401 we built,found valve guides too tight on cold engine & would pop & fart uintil physicly warm thenguides would expand & springs were strong enough to close valves quickly. this was a bitch to find because compression & all looked fine & only act up dead cold,ck w/vacume gauge for pulsation or needle vibrating @ idle & quits when warm & runs fine. turns out machine shop left several guides unpolihsed after valve job----pricks outta buss. at least. he wont screw anybody else

electrican · Dec 18, 2011

m ight should have added that this just started all of a sudden. It is on a running dailey driver. Been fighting this for about three years, but only does in the fall and winter time. Truck has around 100,000 miles on it.

COLT · Dec 18, 2011

Check your EGR. They dont normally screw up on this motor but it is a possibility. Also see if you can scan it af start up and look for variances. Goodluck. Maybe doctordick can chime in.. he's great with tbi stuff!

electrican · Dec 18, 2011

me and dodctodick has already brain stormed this this to no avale. He let me borrow the TBI to try on it . Disconected the Egr and didn' help any.

gomer pyle · Dec 19, 2011

you should stick to fords :flipgotcha:

Elliott · Dec 19, 2011

I've got an 87 that when I bought it the egr had been cut out it would just miss a
Little when cold but nothin bad.

Elliott · Dec 19, 2011

Try a leak down test on the motor, and take the valve covers off and measure valve lift, sounds like it might be mechanical instead of electrical.

rockbuggy · Dec 19, 2011

Whats the fuel pressure on both the feed and return?
Is there any change as it warms up?

Will the engine rev up and smooth out or does it sputter and spit at any rpm when cold?

Does this have the heated adapter between the tbi and the intake or is it using a tbi intake?

Have you looked at the injectors with a timing light to see what the spray looks like hot vs cold?

how long does it take to smooth out?

About what rpm is it running at when sputtering?

what is the voltage at the injectors when its running bad?
One wire should be hot all the time the Ecm Grounds the injector to fire it.

is there any under drive pulleys on the engine?

budman · Dec 19, 2011

my buddys done the same thing the mechanic that fixed it replaced the modual in the distributer

doctordick · Dec 19, 2011

rockbuggy said:
Whats the fuel pressure on both the feed and return?
Is there any change as it warms up?

Will the engine rev up and smooth out or does it sputter and spit at any rpm when cold?

Does this have the heated adapter between the tbi and the intake or is it using a tbi intake?

Have you looked at the injectors with a timing light to see what the spray looks like hot vs cold?

how long does it take to smooth out?

About what rpm is it running at when sputtering?

what is the voltage at the injectors when its running bad?
One wire should be hot all the time the Ecm Grounds the injector to fire it.

is there any under drive pulleys on the engine?

This is a pretty weird problem. Actually had two different problems, it had a bad flowing injector on the O2 sensor side of the exhaust causing the other side to run rich (sensor detects lean condition) and poor throttle response after it was warmed up. I loaned him a throttle body with known good injectors and this corrected that problem but it still has the other problem.

Apparently the other problem started all of a sudden quite a while back and only occurs when the engine temp is below about 65 degrees (engine temp) and continues to about 100 degrees then clears up. At 65 degrees, the ecm is in open loop operation and seem to be OK once it goes into closed loop.

I'll try to hit your points one at a time. Fuel pressure is around 18 lbs, I'm not sure what it should be on that big block since they run 55lb injectors, but it apparently runs well now once it warms up a little. It evidently won't pick up revs at all when cold. Don't know about the heated adaptor, but he says it's all stock (tow rig). He did mention a 2 pin connector laying loose on the pass side near the IAC connector. It does not have the intake air temp sensor in the air cleaner so I kind of assumed that's what that connector is. I've never seen a heater on a small block, is that something unique to BBCs? Normal operation when warmed up would seem to elimiinate an injector voltage problem and everythiing is apparently original, no pulleys or other changes. The problem evidently started suddenly without him making any changes. Budman, in my experience those distributor modules either work or they don't but that doesn't mean it couldn't happen. He has another distributor he was going to swap out this weekend. Since he posted up this AM, I guess that didn't help.

He has changed coolant, O2, and MAP sensors. I'm thinking maybe a fault in the cold start routine in the prom since it seems so consistent but that's a long shot. When he changed the ECM he put his original prom in the new ECM. This one's got me pretty well stumped so any suggestions or SWAG (scientific wild ass guess) is appreciated. :dunno:

Just for my own education, does anyone know for sure what the fuel pressure should be? Also, tell me more about this heater biz.

sappmann · Dec 19, 2011

9 to 13 psi

rockbuggy · Dec 19, 2011

Stock Fuel Pressure for Big and Small Block TBI should be 9 to 13 pounds Except for a few years 1994 and 1995 Big blocks Only I think then it was 26-32 or something like that with a smaller injector.

(They will actually run of a mechanical pump but will not run well)

My Voltage guess was a bad cell in the battery. It may have enough to start the engine but the draw from the starter pulls the entire system voltage down not so low that it wont run but low enough so its not getting the power it should and spark and fuel are not doing what they should. Cold weather hinders battery performance. For a test try starting it when Its cold with a charger on it (not some little trickle charger but something larger or jumpers from another rig).

A standard GM alternator will not induce until about 600 RPM (more if you put under drive pulleys on)

Below is a photo of the Heated adapter that gm ran on the big blocks. It adapts a standard Qjet Manifold to a tbi. From what I understand GM headed the adapter to attempt to help atomize the fuel and keep it from icing up under certain conditions.

Another thing to check is the IAC. Make sure its not bound up or stuck when cold. You can test it on a cold engine by Shorting out the terminals (like you were gona check codes via the dash light) when you do that The ECM will run the IAC all the way out to the end closing the passage. Once closed when you crank it it should open quite a bit to keep the engine running with the high flow rate on the injectors.

You can also do a simple test to see if its electrical in the injection system. take a spare temp sensor unplug your factory sensor and plug in the spare (Have 2 cups of water one below 65 deg and one thats hot to the touch. Just plop the sensor in each one if its in the injection you should be able to make and cure the problem by just moving the sensor cup to cup

Does the problem still persists even with the spare temp sensor in warm / hot water (let it sit in that water for a few min before trying to start so it gets a warm reading.

Does it crank a long time to start when cold like its starving for fuel?

Also Verify that the EGR is closed and not sticking if It still has that take the vac line right off and plug it.

Check for water in the fuel. The TBI injector will pass water no problem however until the engine is warm it will run really bad.

What do the plugs look like?

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doctordick · Dec 19, 2011

I know 9 to 13 is right for a small block, but are you sure that's correct for a big block? Small block injectors are rated at 38 or 42 lbs/hr, and I know big block injectors are rated 55 lbs/hr. Stands to reason that the big block would require higher fuel pressure. Or not.

sappmann · Dec 19, 2011

it carries the same pump for sb and bb

doctordick · Dec 19, 2011

Electrician (sorry, man I forgot your name already but I can "cause I'm old) said he was reading 18psi (put "T" in place of inline filter) which would be high enough to cause it to be too rich at cold idle. Since the throttle body w/reg (and IAC) has been replaced, about the only thing which could cause high fuel pressure is a plugged return line. Believe it or not, I've actually had that problem, dam mud dawbers got in the line while I had the fuel cell out. I guess you could check by disconnecting the return line and seeing if there is any fuel flow. If the truck has the flex lines from the TB, you should be able to disconnect underneath the vehicle where the flex joins the hardline. Hadn't thought about water in the fuel, good call. Poor guy won't have time to check nuthin tonite, he'll be busy trying to read all of this :****:

rockbuggy · Dec 19, 2011

Here in the North East look for any return line that goes through a Metal bracket holding it to the frame as the bracket rusts it will push in an collapse the line. We have run into this alot on front break lines in cars. It will restrict the flow and cause all kinds of problems.

18 psi is kinda high. and definatly could cause overfueling at low rpm's

electrican · Dec 19, 2011

Ok here we go. (My name is Jimmie Smith) and sorry not the buggy builder LOL . Have already put a new battery thinking that low voltage might be the problem The alternator got checked at the same time it tested good but had a bearing that didn't sound too good so it got a new one of those. It does still have the heater adaptor thing under the TBI. The plugs are clean like they should be. Don't believe that it would be water in the gas since it has been doing this in the winter time for 3 years now. But I have been wrong before well maybe several times on this problem. After it warms up youo couldn't ask for it to run any better.It starts sputtering as soon as you press on the gas unless it has warmed up for a few mnutes.The only mods that the truck has had is a set of Headman Headers installed on it before I purchased the truck. It didn't start this problem until after I had owned it for a couple of years.Replaced the complete distributer this weekend and to no evail the same problem exists.

electrican · Dec 19, 2011

Came in this evening and read the book that everybody wrote appreciate the help though. Went outside and started the truck up it is 52 degrees outside and it ran fine . Will check in the morning again when it is a little cooler and see what happens then. This is what I mean by it comes and goes .

By the way Gomer Pyle I wish I had a ford to replace this thing with. LOL LOL