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318 TBI unstable idle and lag when accelerating

33K views 30 replies 7 participants last post by  340SHORTY 
#1 ·
Hi
I Don't have Ramcharger but decided to post here because I know you guys are knowledgeable about TBI
I bought Dodge b250 few months ago, it's 1989 TBI 318 and I'm spending a lot of time trying to solve his puzzle.
my 318 have big problem with Idle RPM and throttle response.
Idle goes up and down about 100RPM, it happen suddenly and quite often.
Other thing is that it have huge lag/bog when I hit the accelerator pedal(under load engine dies) and backfires ( without doghouse and air filter it could burn eyebrows and scare to death...) everytime engine come back to idle it goes a bit too low, 400-600 RPM before ISC react.
What I did :
- Disconnected ISC --> No difference, so ISC is just doing corrections and it works.
- Cutted exhaust pipes after manifolds(before it had single pipe with lame catalytic converter) --> and it helped, engine is not dying anymore, can't see any backfire and it sounds great!  still have other problems
- Different ignition advance setup --> No difference
- Changed spark plugs(gap checked), and all of them are getting good spark
- Throttle body disassembled and cleaned several times and it wasn't as dirty as I was expecting, new gaskets, --> No difference
- Cleaned all vacuum hoses and solenoids, sealed vacuum tree --> No difference
- No fault codes after keydance (12 55)
- New fuel filter
- Cleaned computer, connectors, checked for good ground
- New engine oil and filter
- Have been running with injector cleaner in fuel
- Checked fuel pressure, it stays strong at 14,5 psi even at road test when i was forcing it to stall
- Checked other mapsensors(including GM) and their voltage --> No difference, at least not I was looking for
- Injectors have 1.8 Ohm resistance
- TPS checked voltage, don't remember what it was but was changing in proper range
- Tried to look at injectors spray pattern, it's cone shaped but I don't have enough experience and good strobe light to determine what i see is good or bad, I'm also not experienced in searching for vacuum leaks.
- EGR I think is not working, it have completely rotten cap(I can put finger inside it), plugged vacuum hoses, tried to remove it but these bolts are welded !!

Already removed Air pump, cat, air conditioning, changed fan to electric.
It's not a daily driver or work horse and I want to wake up this motor in closer future so I consider carb conversion.
My last mileage was 10mpg with 70% city driving and cast iron right foot, I don't know what numbers should do TBI in good condition.

I had before 2 cars which were EFI and my experience is that it's much easier to get used to the problem, drive it and sell your fuel injected problem to someone other (it doesn't mean that did nothing to solve it).

I'm asking all of you for help because I'm running out of ideas.
Thanks
 
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#2 ·
You've covered a lot of bases. Good work. Sure there is no exhaust gas getting back through the intake?  That still wouldn't explain the idle surge. Does the timing stay steady, timing chain tight?
 
#4 ·
most 1988 to 1991 TBI problems [1989 is the worst] can be traced to a wiring problem / and its the connectors at the back of the right valve cover / the picture below is extravitgated to show detail

[smg id=2167]
 
#5 ·
I cleaned those connectors too, that was the first advice I found when i was searching this forum.

well I didn't tried to set timing professionally, just checked what happens when i set it in other position, and after came back to original setup.  I don't know in what shape is timing chain, I haven't changed water pump

EGR and its hoses has been messed by previous owners
Today I checked EGR pipes going from exhaust manifolds and they looked like may cause serious leak, so I plugged them and pipe to airpump, engine was running still the same but I noticed that it is sucking air from pipe which was connecting egr valve and airpump.
I'm still confused but at least I know I have to get rid off that valve. I wanted to mount blockoff plate there before but gave up when i saw these bolts.
I'm buying better intake manifold and in the meantime I'll be trying to do something with egr valve
 
#7 ·
I don't have workshop full of finest tools but I'm just in the beginning of my collection. I try to check as many things as possible in easiest way. And you are right, I should plug in vacuum gauge, check compression and set ignition by using good strobe light and disconnecting temp sensor.
I tinker with EGR right now and I'll let you know about effects later
 
#8 ·
No one says they all have to be new or extra expensive. The items mentioned used to be normal do it yourself tools. Think of the time spent already. That cost money. Some of these items are free loaners. Many are dirt cheap at auction swap meet or classifieds.

If you are going to mess with the egr, see if you can safely get some heat to it. Probably cant. If not, run it hot and soak it with kroil. You will have to buy the kroil online. Pb blaster or wd40 will just leave you frustrated.
 
#9 ·
OP

I have a similar issue to yours but when I went to check the timing my light was weak and I didn't see the mark anywhere. Now I have a problem of is it the weak light or is the timing off to the point the mark is not visible.

Like stated you need to verify the timinig is correct by a timing light, not best vacuum like on an old school motor.

Does it start easy?
 
#10 ·
greenpigs said:
OP

I have a similar issue to yours but when I went to check the timing my light was weak and I didn't see the mark anywhere. Now I have a problem of is it the weak light or is the timing off to the point the mark is not visible.

Like stated you need to verify the timing is correct by a timing light, not best vacuum like on an old school motor.

Does it start easy?
You unplugged a sensor to check it? If you just hook up light without putting engine in limp home mode, timing will be all over the place.
 
#12 ·
If the bulb is dim, that is squarely the fault of the timing light or battery. The light is not supposed to vary brightness based on any engine factors.

On the other hand, it does help to clean balancer and pointer along with using a white paint marker on any lines or pointers or numbers.

If your balancer is real greasy and looks like front seal is or was leaking, and marks are no where near, you will probably have to replace the balancer. In that case, the outer ring has likely slipped from the rubber. Can even explode apart if separation is bad enough. Usually caused by oil damaging rubber, from a front seal leak. Crank speedisleeve may be required if grooved.
 
#13 ·
I agree and it is a cheapo timing light so most likely the culprit.

The balance is clean but a bit rusty with no oil of any sorts, also with a white marked line & I cleaned the timing mark area before hand.

Time to get a better quality timing light and check again.

 
#14 ·
Today I mounted blockoff plate instead of egr, I have done computer reset and road test.
there still is a problem, the only thing that changed is the idle at Drive/Reverse, now its rather 600 than 900 rpm like on Park/Neutral. It's my first car with automatic transmission so I don't know how it should behave.
In moment like this I'm thinking about carb swap.
 
#15 ·
Still havent done simple tests and yet consider much more labor plus $750 in new parts that may not solve the problem? Im sure once that cost sets in along with knowing the fact it may not solve the problem, will help you see the error. If not, it can be an expensive lesson.

So far, there is no evidence of a fault in the fuel injection system specifically. Until you have proof of out of spec parts, refrain from any total system replacements.

Conversion to carb will also require a timing light to time replacement dustributor and vacuum gauge to tune carburetir. Miral of story? Whether you like it or not, the tools are needed.
 
#16 ·
Hows your O2 sensor?

My 91 TBI was not happy at all until I got the O2 sensor in good working order and in a good place. I had headers so I had to move it off the manifold.
 
#17 ·
I think computer relearned and now all is like before removing egr
I'm collecting tools right now.

The only code it flashes is about iSC because I disconnected it for a while, so O2 sensor seems to work, Am I wrong ? there also should be difference in running cold/warm engine because sensor need to heat up. when it's broken, computer takes his factory saved data to work(limp mode) and should throw fault code.
I can try to disconnect it and see what happen

I'm curious where exactly did you placed sensor, I'm looking for headers.
 
#19 ·
lately I focused on injectors spray pattern, but this time I used strong light and found something interesting. They are spitting ! hard to see at idle, I kept him at stable mid rpm(about 3000) for more than few seconds and and I saw random spitting like a double dose of fuel.
I hope its the cause of my problem.
Its worth noting that injectors seemed to be in great shape when I pulled them and I also added STP injector cleaner to tank some time ago.
I'll take them to ultra sonic bath cleaning on Monday.
 
#20 ·
Installed the new injectors and they still work the same way. I think computer is sending bad signal to injectors. In the meantime I bolted headers and edelbrock 2176 intake, carb will be next so I'm not gonna spend more money on TBI system.
Thank you for your help guys
 
#21 ·
How are you going to fuel this carb? The stock pump will blow the carb internals "apart". Perhaps not actual destruction but the fliat needle ans seats wont hold it back.

Dont forget the kickdown cable.

And the voltage regulator.

And the electronic ignition.

You are looking at $1,000 by time its all said and done counting the price of headers. Aint even half way through the conversion yet.
 
#22 ·
I already did research about that mod, including this forum
adjustable fuel pressure regulator 30-60$ in my country
refurbished carb 225$
carb calibration kit 40$
ready to run dizzy and coil kit 80$
still not sure about kickdown cable/rod but I can fabricate my own if I'll have to do it
I'm not from U.S so I appreciate any help
 
#23 ·
Can you show a link for a bypass regulator under $50 from your region? Bypass tend to be more expensive than regular (dead head) and cost around $70 give or take.

The rest of your prices are inline with the US and on target for the previous mentioned price quote. (Counting intake and headers)

The voltage regulator is also not a big deal and the kick down parts are slightly more than $100.
 
#25 ·
http://moto.allegro.pl/regulator-cisnienia-paliwa-uniwersalny-nowy-i2627121839.html
http://moto.allegro.pl/regulator-cisnienia-paliwa-uniwersalny-komplet-bar-i2622540370.html
http://moto.allegro.pl/regulator-cisnienia-paliwa-uniwersalny-nowy-i2609406719.html
http://moto.allegro.pl/regulator-cisnienia-paliwa-uniwersalny-silver-i2609954944.html
1PLN = 0.32 USD at the moment
I bought used intake for 100$, used headers were very hard to find so i bought new for 200$,
and it works, even with that small throttle body and that Amiga,Atari alike ecu

Captain Obvious I've got a feeling that you are trying to catch me on hypocrisy
 
#26 ·
Nope, i just dont want you to skip something and damage more of your dodge or have stuff still not work.

Lotta people asking stuff like "how do make my fuel pump work?" Why wont my alternator charge ir why dont i have spark? Or why does my transmission slip.

Some go on to tell others they can do the job for "a couple of hundred" and were shocked to find the total estimate. I just put the info out there as complete as i can.

Other people may read this thread, then they will find out more about cost and things involved.
 
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