FML I'm at wits end with this engine. 95 350TBI 185k. Ran terrible when I got it so I've replaced EGR valve/solenoid, full tune up, ignition control module, temp sensor, fuel filter. Ran great for 6 months then started acting up again, same symptoms. It drives terrible, gets terrible mileage, stumbles at idle, stumbles at part throttle, surges and falls on its face basically all the time driving or idling. I cant figure it out.

Fuel pressure is at 12psi, timing is at 0 degrees with plug unhooked. I haven't found any vacuum leaks, all grounds are good and there is no check engine light. I have to dd this pos and its getting increasingly irritating trying to drive, especially since I cant figure out whats wrong. From what i can tell the injectors look to be spraying fine.

Any ideas on where to go now? I'm out of ideas. Thanks fellas

 

Any vacuum leaks?

 

None that Ive found. I did the whole carb spray around tbi/intake thing and didn't hear any changes in idle. im wondering if compression might be an issue. The engine has had a hard life and it burns a fair amount of oil. Any thoughts?

 

low compression would cause hard starting, and it wouldnt have went away for 6 months and then come back IMO

 

What do your plugs look like?

The tbi CTS is known for frequent failure, check the connector, test or replace the sensor.

 

I would check if SES is functional - move ignition key from off to run, but do not start engine. SES should be solid, blink off turn back to solid on. During this time you should also hear fuel pump come on for about 2-3 seconds. Once engine starts SES should be off. I have seen PO's remove SES light from the socket instead of addressing underlying problem! Light bulbs also burn out.

Small hat dizzy are notorious for cross fire - check inside distributor hat for rust looking streaks. If you have those time to replace spark plugs, wires and dizzy parts.

As was mentioned before after market CTS are prone to 'soft' fail - ECM changes fuel mixture based on CTS input. Generally CTS failure (CTS high resistance or open circuit - yellow wire) sets of DTC 15.

//RF

 

SES is functional, it comes on when I unplug the ignition connection to test timing. Just as a side note I was shinning the light at the timing marks with the connector hooked up and when I revved it timing advanced crazy high.. Is this normal or do I have something else wrong?.. Gonna throw some more plugs, cap, rotor at it in the morning and see if their is any improvement. IDK what else to do after that.

 

Lets clarify something - when you say 'unplug the ignition connection' you are referring to single circuit set EST connector (light brown/white wire) next to power brake booster?

With EST reconnected ECM controls timing at idle most truck calibrations will result around 17 to 20 deg at normal operating temperature. As RPM climb timing will climb as well (depending on calibration, RPM, MAP)

//RF

 

[quote=RFmaster;4713298]Lets clarify something - when you say 'unplug the ignition connection' you are referring to single circuit set EST connector (light brown/white wire) next to power brake booster?

yes

 

Well I went ahead and stuck some new injectors and did a rebuild on the TB, gutted the old cat and put a new cap and rotor on it. Its better but not gone. I would guess at this point that it is something in the dizzy itself, what exactly I dont know. Guess Im just gonna live with it until I buy another one. Any ideas on what brand to buy?

 

Small hat dizzy uses external coil - before swapping dizzy I would get a another coil (from JY or from a friend) just to make sure that it is not flaky. Also, performance after market coils do not match OE ICM well. IMHO, I would stick with a rebuild OE dizzy- for cost reasons. As a side note the only things that can go wrong inside dizzy - ICM, reluctor coil and/or magnetic trigger wheel.

//RF

 

ok one thing I have to ask......, What computer are you running? if you're running the stock comp that could be your issue right there. When switching to a 350 if running close to stock you NEED to use a 350 comp.

 

I appreciate you guys help. Its running a 350 ecm. Couple more questions. What are the odds that there is an internal problem within the dizzy? From my limited knowledge those don't really seem like parts that would fail intermittently. How long do they typically last? The engine has 186k on it and as far as I know (truck has been in the family since new) the dist or coil have never been messed with. Ill def start with a new coil since they are only $20 but I hate to keep throwing parts and money at this thing with the hopes of eventually fixing the issue. I guess its kind of too late for that already though.

 

There have been several post over the last two years that eventually were narrowed down to a combination of distributor and coil:

https://www.thirdgen.org/forums/tech...ont-start.html
https://www.thirdgen.org/forums/tech...k-but-not.html
//RF

 

Ok I swapped out the coil cleaned all the connections/mounting points and double checked the timing to 0 degrees again just for good measure. That seems to have taken care of 99% of the problem. The miss/stumble is still fairly prevalent at idle but it no longer misses when its under load. Any idea why the idle miss? I can live with it but it still drops rpm low enough at times that it almost wants to die.

I know these engines are typically happier with 2-4 degrees advanced timing, would that help anything or am I better off leaving it alone? It was a tad advanced before today (about 2-3 degrees) and I could tell a difference in power. That could have been part of the problem I guess... Thanks for all the advice guys, it really helped out.

 

Give it 2 - 3 deg, but remember that will advance timing across the board. Minor miss at idle maybe due to a weak cylinder. On a high millage engine you may have one or two cylinders that maybe running lower in compression. FWIW, I like to run my stock TBI engines at 14-15 PSI - results in better fuel spay pattern. 12 PSI is adequate. I would run cylinder leak down test to find weak cylinder. Timing Chain stretch may result in weird timing. Good luck with it.

//RF

 

You definitely need to check your tps. I just went through the exact issues you are talking about. My tps was defective, replaced it with a brand new one that ended up being not quite as defective as the old one! Use a voltmeter to test the voltage.

 

Update:
Well, I almost got a full day of normal driving. Its slowly but surely coming back, getting a little worse every time I drive it. Unbelievable what a lame duck PITA this pile has become in the last 6 months.

Does this sound like a TPS issue? Throttle position doesn't seem to correlate with my problems. Wouldn't a malfunctioning TPS throw a SES? I'm starting to wonder what the purpose of that stupid light is anyway. The only code I've ever seen it throw in 10 years was a 32 EGR code which I replaced.

Dizzy is tight, timing is a 0 degrees, cap is tight, coil connections are clean and grounded, plug wires are seated, no vac leaks and injectors are not leaking. I'm really frustrated at this point.

My guess is still something internal with the dizzy. Last time I replaced the cap/rotor it ran good for 6 months before acting up. This time it barely made it 24 hours before becoming noticeable again. It's not as bad yet but I have a feeling by weeks end I'll be back to square 1 only minus another $200 in parts. I'm sure a couple cyl are probably low on compression but there isn't anything I can do about that on my remaining budget of zero dollars. Any ideas?

 

It was the coldest day of fall this morning and when I started it up and drove and it ran great barely missing at all. If my thinking is correct, the reason it runs worse when its warmer is because the ECT sensor is giving an incorrect reading to the ECM causing it to run rich? I hope, so Ill replace it again (its been 8 or so months) and see if that helps anything. If nothing changes, IMO the only other thing it could be is the distributor. My problems seem to be pretty common to most, so for lack of any SES codes or any evidence of a TPS problem that's my guess. Any thoughts?

 

Put in a new ECT and threw some plugs at it while I was in there. Fixed!!! Plugs looked good for the most part except #4 was covered in something..IDK what it was but hopefully this thing will run for a while now. Thanks goes to this forum. Appreciate it!

 

I'm happy it's doing better.
Keep an eye on that plug, if she starts acting weird again check it right away.

While I'm here thinking about it...check that plug wire w/an ohm meter.

 

I got question for you guys the car i bought the guy said its a 350 tbi? how would you know if its a 305 or a 350. I would appericate if you would show me a pic because i would be even happier if it was a 350 tbi. It runs and sounds like it is.