'88 TBI 350 - multiple personalities

[brendo613]

Vehicle is a 1988 GMC Vandura 2500, TBI 350. When cold sometimes it stumbled upon acceleration. Sometimes it idles high and slams into reverse or drive. Sounds like an intermittent vacuum leak, but now the problem is compounded.

Vehicle now won't start without 1/2+ throttle opening. Runs very rough, eventually smoothes out, but idles low. IAC looked good (until I cracked it overtightening it upon reinstall). Code 15 (coolant temp sensor) is in memory.

Where do I begin with this intermittent mess? Carb & distributor swap?

 

[HotRodPC]

Vehicle is a 1988 GMC Vandura 2500, TBI 350. When cold sometimes it stumbled upon acceleration. Sometimes it idles high and slams into reverse or drive. Sounds like an intermittent vacuum leak, but now the problem is compounded.

Vehicle now won't start without 1/2+ throttle opening. Runs very rough, eventually smoothes out, but idles low. IAC looked good (until I cracked it overtightening it upon reinstall). Code 15 (coolant temp sensor) is in memory.

Where do I begin with this intermittent mess? Carb & distributor swap?

Now you know why vehicles are referred to as "her", or "she" or usually named after women. Cuz they can be real bitches !!!

Have you considered an ignition problem? Bad plug wire, cap or rotor, a fouled plug. But that isn't going to cause the high idle situation you mention. How about EGR valve? It can be stuck partially open if it's got alot of carbon build up on it, allowing an internal vac leak at idle if it was not able to close off and the pintle go all the way home where it rests shutting it off. That also won't throw a code either.

 

[brendo613]

Haha, good points all around, HotRod. Thanks for the laughs on an otherwise deflated day. Just put a new trans in and was looking forward to a test drive.

EGR, plugs, cap, wires are new with maybe 3000 mi on them. The injectors spew fuel out. EGR and IAC get flooded with fuel every time I've had them off in various diagnosing. Reckon the TBI system is running the engine rich. Way rich.

Only 100k on the vehicle, too. Carb & dizzy swap looking mighty good right about now.

 

[Jims86]

Haha, good points all around, HotRod. Thanks for the laughs on an otherwise deflated day. Just put a new trans in and was looking forward to a test drive.

EGR, plugs, cap, wires are new with maybe 3000 mi on them. The injectors spew fuel out. EGR and IAC get flooded with fuel every time I've had them off in various diagnosing. Reckon the TBI system is running the engine rich. Way rich.

Only 100k on the vehicle, too. Carb & dizzy swap looking mighty good right about now.

Carb and dizzy swap is a copout. Get a rebuild kit for the throttle body, sound like your injector seals failed. You will obviousely need a new TB base. i think HR may have a location on an extra, if Im not mistaken. there may be a few others floating around as well. Get an AC Delco cts to replace the bad one.

If you do go with a carb swap, keep in mind, cold starts will have an extended cold idle time, and will drive like dookie until warmed up. Stay away from Edelbrock carburetors, go with a 750 CFM Quadrajet, or a Holly Truck Avenger.

 

[Jims86]

Haha, good points all around, HotRod. Thanks for the laughs on an otherwise deflated day. Just put a new trans in and was looking forward to a test drive.

EGR, plugs, cap, wires are new with maybe 3000 mi on them. The injectors spew fuel out. EGR and IAC get flooded with fuel every time I've had them off in various diagnosing. Reckon the TBI system is running the engine rich. Way rich.

Only 100k on the vehicle, too. Carb & dizzy swap looking mighty good right about now.

Duplicate post

 

[brendo613]

Copout - guilty indeed. While wagering TBI parts bill against carb swap bill, quadrajet & HEI thoughts came to mind. GAS (gear acquisition syndrome) strikes again. TBI base is okay because the IAC came out broken, but in one piece. Thank you though

The injectors drip inbetween fuel pulses, but hold pressure with fuel pump on & engine off. Figured that ruled out injector seals. Couple months ago I removed the injecotrs, opened / closed them with 12v, and shoot cleaner through them; no change in spray pattern, though. This was a last-ditch effort in lieu of replacement @ $75 / ea.

Will have to check TPS. Perhaps if the ECM interprets a different throttle position than is exhibited, this would cause rich running / incorrect IAC position. The intermittent high idle has always been an issue with the van. Made for nasty gear slams, and screwy shift points. This issue must be corrected before I harass the new transmission with a poorly running engine!

 

[Jims86]

Copout - guilty indeed. While wagering TBI parts bill against carb swap bill, quadrajet & HEI thoughts came to mind. GAS (gear acquisition syndrome) strikes again. TBI base is okay because the IAC came out broken, but in one piece. Thank you though

The injectors drip inbetween fuel pulses, but hold pressure with fuel pump on & engine off. Figured that ruled out injector seals. Couple months ago I removed the injecotrs, opened / closed them with 12v, and shoot cleaner through them; no change in spray pattern, though. This was a last-ditch effort in lieu of replacement @ $75 / ea.

Will have to check TPS. Perhaps if the ECM interprets a different throttle position than is exhibited, this would cause rich running / incorrect IAC position. The intermittent high idle has always been an issue with the van. Made for nasty gear slams, and screwy shift points. This issue must be corrected before I harass the new transmission with a poorly running engine!

Qjet is a good option, but what are your inspection Laws? There is a guy in PA having problems passing because a bunch of stuff is disconnected. As far as injectors, you could send them to Wtchhunter.com to be cleaned and tested for $22 each, this is who I use if I cant clean them.

 

[bucket]

... Code 15 (coolant temp sensor) is in memory.

Am I the only one that saw this? I've had a CTS crap out on TBI motors a couple times, they do funky stuff and run like crap. Start with a new CTS and check the condition of the wiring to it!

 

[Jims86]

Am I the only one that saw this? I've had a CTS crap out on TBI motors a couple times, they do funky stuff and run like crap. Start with a new CTS and check the condition of the wiring to it!

Post #4, end of first paragraph.
A bad CTS will never dump that much fuel to have Droplets form from the injectors.
Just had a wild thought....With the fuel pump running in prime mode, engine off, key on, what happens?

 

[brendo613]

Inspection - good point. I have a station who would let it slide, but it isn't "right."
Witchhunter, only $22 - reckon this is what I'll do. The price is right!

Fuel pump prime mode - skip over my previous post, why I oughta ...

The injectors drip inbetween fuel pulses, but hold pressure with fuel pump on & engine off. Figured that ruled out injector seals.

Agreed the CTS could louse the mixture up, but not this badly. Maybe compounded with leaky injectors it all runs too rich.

I wonder what resistance the CTS should read at certain temperatures. One must identify faults before trying theories. Anyone know what its range should read? Handy dandy infrared thermometer is ready to be whipped out (no, that's not a pickup line).

 

[Jims86]

Inspection - good point. I have a station who would let it slide, but it isn't "right."
Witchhunter, only $22 - reckon this is what I'll do. The price is right!

Fuel pump prime mode - skip over my previous post, why I oughta ...

Agreed the CTS could louse the mixture up, but not this badly. Maybe compounded with leaky injectors it all runs too rich.

I wonder what resistance the CTS should read at certain temperatures. One must identify faults before trying theories. Anyone know what its range should read? Handy dandy infrared thermometer is ready to be whipped out (no, that's not a pickup line).

What I was getting at with the injectors, is that it makes complete sense that they hold pressure without pulses. But with the key in the on position, you only get around a 2second prime shot from the pump, then it shuts off untill it senses oil pressure. What I wanted you to try, is to add power to the fuel pump manual prime circuit(red wire pigtail on fuel relay plug, or pin D on the diagnostic connector) so the pump runs constant. And then turn the key to the on position, which adds power to the injectors. The ecm fires the injectors using ground pulses. If it holds pressure, then my thought of chassis chaffing, grounding the injector trigger wires is unfounded.

GM TBI does not hold pressure when the pump is off, like Multiport fuel rail setups do.

 

[89Suburban]

It didn't do this before the trans swap? Kinda coincidental?

 

[Jims86]

It didn't do this before the trans swap? Kinda coincidental?

I cant think of anything that would happen due to a swap, short of the engine teetering so far back, that it cracked the plastic vac fitting to the Brake booster, or ripped another vac line off somewhere.
No leaks at the exhaust collector on the drivers side? Maybe reversion getting to the o2?

 

[brendo613]

It used to run poorly at times, but now the times it runs well are a memory

CTS read open @ 72 F. Sounds poor to me. Ordered a complete TBI gasket kit, pickup coil, coil, ign module, IAC (cause I broke it), heater core (blocked with stopleak - not my doing), and I'm having the two injectors cleaned by Witchhunter.

Before I remove the injectors though, I do want to try what you mentioned, Jim. Pin D to 12v ... is there a convenient 12v tap in the ALDL?

Good to see the CTS reading incorrectly. ECM's code 15 was correct. There's a little flashy man friend I've made with that SES light. I'm rather amazed how poor the engine runs with a bad CTS! Reckon that and the leaky injectors made for my problems. The other parts are purchased as preventitve maintenance items. I'd rather keep the original, working parts as spares, rather than be at the mercy of the original parts' failures.

 

[Jims86]

It used to run poorly at times, but now the times it runs well are a memory

CTS read open @ 72 F. Sounds poor to me. Ordered a complete TBI gasket kit, pickup coil, coil, ign module, IAC (cause I broke it), heater core (blocked with stopleak - not my doing), and I'm having the two injectors cleaned by Witchhunter.

Before I remove the injectors though, I do want to try what you mentioned, Jim. Pin D to 12v ... is there a convenient 12v tap in the ALDL?

Good to see the CTS reading incorrectly. ECM's code 15 was correct. There's a little flashy man friend I've made with that SES light. I'm rather amazed how poor the engine runs with a bad CTS! Reckon that and the leaky injectors made for my problems. The other parts are purchased as preventitve maintenance items. I'd rather keep the original, working parts as spares, rather than be at the mercy of the original parts' failures.

It will be pin G actually. No voltage in the aldl usually, but go to a shunt on the fuse box, and it should do what you need it to.
Ya know, since you needthe doghouse off anyways, go ahead and pull the plug on the oil pressure switch(unde rthe disstributor)and cross it with a paper clip. Some ALDL's dont have the pump prime wire...confirm your does, it should be red with a white stripe.