Recently done a 350 TBI swap. L98, stock cam, headers+3in exhaust, mildly ported heads, 15lb spring, bored TBI and intake. Good chip tune on it car has ran great the first 3 months couldnt be happier. Now.. Every now and then for no apparent reason or warning you can be cruising along and get in the throttle and it feels like a 4cyl and not a turbo 4 cyl. Also when it does this the engine will warm way up to around 220+. I have a 180 thermostat and a fan switch that turns on @200 and off @180.. Until this week I havent ever seen it hardly get above 180 and no hiccups in the way its ran so far.We checked fuel pressure when doing the install and had great fuel pressure in fact the fuel pump has been swapped to a higher flow at some time or another as it was putting out almost 60 lbs pressure.Im wondering if I may have an injector sticking making the car run lean? Will running lean make it heat up? Im just wondering what could be causing this issue. Could it be a crappy distributor?

 

Can you datalog it? Theory of a injector failure sounds good but it's a lot of guessing with no data

 

Connect a scan tool, look at the data stream. If it's lean, you'll see it in the O2 sensor readings. Verify the rest of the sensors and outputs--knock sensor, coolant temp, MAP, etc.

 

MAP SENSOR. Only sensor I did not replace when doing my swap and it was doing some of the same things I had seen a faulty Map Sensor do on an old C10 I had. so I started there. Seems to be running fine now. Idles at lower rpms and smoother at idle than it was for sure. I will put some miles on her next week and for sure see if that was the culprit but pretty sure now it was.

 

Well I guess its on to checking fuel pressure and/or changing injectors because this problem came back again. Seems to warm up and run like crap after an hr or so of driving most of the time so Im thinking maybe fuel pump is getting weak once it warms up? May be a faulty injector? 99% of the time the car runs absolutely perfect and I couldn't be happier. Then all of a sudden temp goes up to 220ish and power goes down the drain . Always something.

 

I'm questioning your distributor too. I don't know if this jives with a computer controlled dist but I had a mechanical that would stick advanced. Is the distributor getting hot and not doing what it's supposed to? Just a theory and not a complete one.

 

Thinking of replacing it. It was a cheapo so I think I will et a name brand with a warranty and try that first.

 

Noticed yesterday my IAT sensor had came undone from where id tucked against the firewall and fell onto the intake so I moved it back. Suspect it may have got really hot and was doing something weird? Also changed coil. Drive 2 hrs last night and over an hr tonite no hiccups... Hopeful it straightened out.

 

Hmm...interesting. I would have thought (dangerous) that a high IAT number would make the ecm throw more fuel at the engine, not take it away.

But better is better. If it's running well, you can't argue with that.

Off topic, what did you end up doing for an intake on that engine?

 

Well it wasn't the IAT. Seems Ive narrowed it down to doing this after car is good and warmed up and after Ive got into the throttle pretty hard. Doesn't do it all the time but did it again the weekend. Upon de-celeration it popped and backfired and was down on power when I picked up throttle again. I pulled over, turned car off a few min then when I crank back up the temp went down and it was back at full power. Maybe its flooding hell I don't know but I will keep playing with It. As for the intake Im using the stock GM TBI intake bored to match my throttle body.

 

I think you're going to have to datalog it or you'll be chasing your tail. Unless you luck into it by throwing parts at it. We know how that usually ends.

 

Ive about threw everything at it I can at this point. Frustrating because with FI it could be anything. Wish Id started with an LG4 or L69 car instead of this damn toilet bowl injection. It ran so good the first couple months and does now most of the time.

 

try unplugging the alternator nd c if the idle is different. im having an issue almost identical but when i unplug the alt it idels beautiful more power nd all. im freaking stumped. ive thrown so much at it checked wires replaced parts nd it still does it. sounds like a tractor when hitting throttle when all is connected. ?????????????

 

Ive narrowed mine down to only doing it after Ive really run it hard after atleast an hour or so of driving. Drove it couple hrs on the hwy to a show Saturday no hiccups. Got close to home that eveningand tore out at a stopsign ran it up to a pretty high speed and she warmed up to 210ish and started running like crap. Im thinking excessive heat from the headers maybe screwing with my distributor or coil? I guess I need to quit flogging on it Lol. In the first 30min of driving you cant make it run bad hardly even showing my *** in it?

 

Try taking a hair dryer to those individual components when the engine is cold to see if you can isolate the issue that way. Just a thought. Perhaps it has enough air flow under the hood on the highway that it keeps something from getting too hot. BTW thanks for suggesting HatfieldsDecals to me, she made me a really nice 1988 style replica fuel injection decal for my air cleaner lid for a great price and was awesome to work with.

 

Got one myself. Yea those folks are great!

 

Looks good on there! In case anyone is wondering about it, that decal is sized to fit a stock TBI air cleaner lid perfectly. I'd post a picture of one on my lid, but it's pretty big and I don't want to derail your thread.

 

High IAT = less-dense air. Less-dense air needs less fuel to maintain the same air/fuel ratio.

Connect a scan tool, find out what the computer is trying to tell you.

Guesses and the Parts Cannon only go so far.

 

No go ahead let's see.

 

This is the stock f-body TBI air cleaner lid, just cut down because I'm making a cowl induction setup with parts from the stock unit. This decal is the prototype, and I had to cut it in sections to get it to fit the curve correctly. I mailed her a template after applying this, she corrected the spread and I bought some more. So I can confirm that they will follow the stock lid correctly now.

I have no affiliation with this store aside from having her create this decal, but if my TBI brothers and sisters want any here's where to get them: https://www.etsy.com/shop/HatfieldsDecals

 

I'd like to see more about this as it comes along...

 

FYI, ECM pulls alot of timing at high coolant temps and possibly even more with high IATs.

 

Don't know if this is figured out yet but I read enough of the thread and this mirrored a problem I had with my 92 bird. Would die and leave me on the side of the road once it got real hot. It would start backup and run real bad and then die again. I threw a few parts at it but diagnosis ended up outside of my mechanical knowledge so took it to a mechanic. I told him I thought it was fuel related so he replaced the fuel pump and fuel filter. We thought we had it fixed and on the way home it died on me again the drive was a 45 minute drive back home. Long story short turned out to be the distributor, started to mess up when it got hot. Someone else earlier in the thread called that out, that may be your issue if you haven't thrown that at it yet.

 

Im betting that's what it is. Havent been driving it a whole lot and when I have Ive took it easy on it and had no issues. Im fixing to change that distributor out and do some other things to it while its too hot to enjoy driving it.