1st TBI Conversion Help Needed

[4WDKC]

I checked for vacuum leaks when we set up the system and all was good. It idles nice and smooth also.

I'll check the thermostat. I'm pretty sure we replaced it not that long ago but maybe its a bad unit.

I've been thinking about upgrading to a higher amperage (150+) output alternator. The plow pump sucks a lot of juice.

When you swapped in the TBI did you reuse the stock line from the tbi to the MAP? I have read using a bigger hose or long than stock can cause problems, not sure how true that is.

I have an 180* t stat in mine with 2 1/8 holes in it, the truck still runs 170* in 10* weather. It takes a while to warm up but it still does.

if you have the v belt setup you should be ale to replace the stock alt. with one from a 92-96 vett, 93-97 Fbody, 94-96 Caprice/Impala/Roadmaster they are 120+ amp. If you have a serp. setup you can do a mod that will allow use of the 140 amp alt. from a vortec or ls equipped truck.

One last thought are we sure the fuel pressure is good?

 

[MtBraun]

When you swapped in the TBI did you reuse the stock line from the tbi to the MAP? I have read using a bigger hose or long than stock can cause problems, not sure how true that is.

I have an 180* t stat in mine with 2 1/8 holes in it, the truck still runs 170* in 10* weather. It takes a while to warm up but it still does.

if you have the v belt setup you should be ale to replace the stock alt. with one from a 92-96 vett, 93-97 Fbody, 94-96 Caprice/Impala/Roadmaster they are 120+ amp. If you have a serp. setup you can do a mod that will allow use of the 140 amp alt. from a vortec or ls equipped truck.

One last thought are we sure the fuel pressure is good?

Yes, the MAP has stock lines. Fuel pressure is about 13 PSI with key on and truck running. Thanks for the thoughts on the alternator.

 

[4WDKC]

Yes, the MAP has stock lines. Fuel pressure is about 13 PSI with key on and truck running. Thanks for the thoughts on the alternator.

Do you have a permanent gauge on it so when it acts up you can look at the pressure?

 

[MtBraun]

I double checked the thermostat and it was a 160 degree unit so I replaced with a 195 degree thermostat and my coolant temps are much better. The only thing I notice is that when idling, if I stab the throttle a bit I get the cutout around 1200 RPMS. I can slowly increase the throttle at idle right through that RPM range with no problem. When cruising, the vacuum drops to the single digits. What is normal? Maybe this is part of my problem.

First picture - sitting in park at 1200 rpm. Second picture - putzing down the road.

I do not have a fuel gauge hooked up to view live, but I'm pretty sure its not a fuel problem. Everything from the tank to the TB is new. And the symptoms are in such a small window RPM wise under certain conditions it would seem to rule out a fuel pressure issue to me. I'm going to go back over all vacuum lines again.

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[MtBraun]

I went over everything testing for vacuum leaks and all is good. the only way I can get it to change idle is shoot directly into the throttle bore. However, I did notice that the injector harness (inside the TB) and the throttle bore is covered in soot...which is coming from when the engine cuts out/backfires through the throttle body?

 

[1987 GMC Jimmy]

I would say that's where it was coming from. If you think of acceleration as a linear graph, an acceleration with a steeper slope will make your vacuum go down more and then recover. An acceleration with a gentler slope will net a lesser change in vacuum. It shouldn't hold at a low vacuum, though, per my testing I did yesterday. That vacuum reading, I think, correlates with your issue. I have no idea how it does, though. I feel bad about this, Matt. I don't think TBI is usually that stubborn, and I know you've put a lot into it. I can usually come up with at least what direction to go in, but this has stumped me. Do you have a vacuum gauge? The baud rate is so slow on the ECM interface that it's hard to see vacuum live like a gauge would show you. It might give a second opinion to what the computer says.

 

[MtBraun]

I've checked for vacuum leaks on all the TB connections, TB base gasket, the vacuum boost brake line, and nothing. Where else could a vacuum leak be coming from? And why do I have good vacuum at idle and then poor idle at operating RPM?

 

[1987 GMC Jimmy]

Everything sealed with your EGR block off plate? The brake booster can leak a considerable amount internally when it fails, but you’d have other symptoms like a loud noise when pressing the brake or a stiff pedal. I’d try pumping up the MAP sensor to see if it’ll hold vacuum properly. Double check the rubber canister lines going in and out until it turns to steel. Make sure the PCV valve still rattles. I think that’s about it that you haven’t mentioned or that I can’t recall you mentioning. The biggest leak site hands down will be your intake manifold gasket. Even if it was that, I can’t explain why it would be acting up at a certain RPM, but if you look at various explanations of analyzing a vacuum gauge, the really low vacuum condition will translate to a pinched or failed gasket of some kind.

 

[4WDKC]

The great thing about tuner pro is that it allows you to data log with no extra equipment, this allows anyone with tuner pro to download the datalog you created and uploaded to the site and watch the values like we are in the seat. Open it up find the acquisition tab and record, then go do whatever you do to make it act up. After your done stop and save the file, then share it here or on gearhead.

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[MtBraun]

I have a couple log files already created capturing the symptoms. I tried awhile back for @1987 GMC Jimmy and this site will not let me upload an .xdl file.

If you would be so kind you could PM me your email address and I'll send you a log file. @4
@4WDKC
Thanks!

PS - I've not had much luck on gearhead. I don't think the site gets the traffic nor has the interested members of GMSB.

 

[4WDKC]

I have a couple log files already created capturing the symptoms. I tried awhile back for @1987 GMC Jimmy and this site will not let me upload an .xdl file.

If you would be so kind you could PM me your email address and I'll send you a log file. @4
@4WDKC
Thanks!

PS - I've not had much luck on gearhead. I don't think the site gets the traffic nor has the interested members of GMSB.

That site has a lot of members that are on alot of different boards and when you have a niche you cater to it tends to not be so active.. for example look at the post dates for threads about tuning these old systems. Where as this board gives a spaces for paint/body, transmissions, differentials, brakes ,tires etc. oh and sent. you could also try zipping the file and see if it can be uploaded like that.

 

[MtBraun]

That site has a lot of members that are on alot of different boards and when you have a niche you cater to it tends to not be so active.. for example look at the post dates for threads about tuning these old systems. Where as this board gives a spaces for paint/body, transmissions, differentials, brakes ,tires etc. oh and sent. you could also try zipping the file and see if it can be uploaded like that.

I hear you on the gearhead site.

I just zipped a log file to this post.

 

[4WDKC]

I saw 253 knock counts, after my heads/cam swap I saw 3 on the drive home. Check your timing with the truck warm and esc wire disconnected. Set to 0 turn off then reconnect the wire, setting this helps eliminate timing as a cause for the spark knock. Also the coolant temp never getting over 155* if the sensor is good, then you may need to replace the tstat, 195 will make the efi work as intended by the designers. What cam or engine is in the engine?

 

[MtBraun]

I saw 253 knock counts, after my heads/cam swap I saw 3 on the drive home. Check your timing with the truck warm and esc wire disconnected. Set to 0 turn off then reconnect the wire, setting this helps eliminate timing as a cause for the spark knock. Also the coolant temp never getting over 155* if the sensor is good, then you may need to replace the tstat, 195 will make the efi work as intended by the designers. What cam or engine is in the engine?

Sorry that may have been an old log file. I did replace with a 195 degree thermostat and my coolant temps were 180 degrees. Didn't change any symptoms though. Engine is I think a stock 350. heads are stock and there was no obvious porting or work done to it when I had them off for head gaskets. Unsure of cam I assume it is stock.

I've been wondering if it was timing and am going to double check that again this weekend. Had a mechanic set it with a light but can't hurt to double check.

 

[4WDKC]

Sorry that may have been an old log file. I did replace with a 195 degree thermostat and my coolant temps were 180 degrees. Didn't change any symptoms though. Engine is I think a stock 350. heads are stock and there was no obvious porting or work done to it when I had them off for head gaskets. Unsure of cam I assume it is stock.

I've been wondering if it was timing and am going to double check that again this weekend. Had a mechanic set it with a light but can't hurt to double check.

was this a carb engine you swapped to efi or did you swap in an entire tbi engine?