Troubleshooting GM TBI

Ok, got me an '87 Chevy... (Don't hate. You know this truck is awesome!)





...It's in amazing shape, mostly. 350, zero rust, perfect body, great paint, interior. It's all stock and everything works. It's probably about $300 worth of Pull-A-Part and LMC and a few weekends away from being 100%. I'm really happy with it. Just a few things to work out.

I swapped my rusty '73 Ranchero for it. And I swapped my nasty old creeper van for the Ranchero. I bought the creeper van for $1000 and a sixpack of Guinness, so I think I did well!

But, it runs like crap and that's probably got something to do with the TBI. It could be as simple as spark plugs, I haven't even checked the basics, but I intend to devote Saturday to resolving this problem, so I want to have every possible cause swimming around in my head when I attack it.

Here are the symptoms:

It has an apparent torque converter shudder and it only happens under lockup. It's a 700R4. This may be unrelated but I'm listing it in case it causes a lightbulb to flash in someone's head. The speedometer also reads low so it might just have a way higher rear gear than it's supposed to. Likely a separate issue.

It doesn't idle too bad in P or N, but in gear it barely idles at all and I often need to use both feet at a light. It may have an intermittent miss while this is happening, hard to tell.

There is usually no Service Engine light on. When there is, it's after I've driven it for a while and it always goes out on its own. I haven't pulled codes yet but I will. Temp and oil pressure are good.

Off idle, cruising and accelerating it does pretty good for a stock 350 pulling a tank, really this is mainly an idle problem.

Here's what I'm going to check this weekend:

Plugs and wires
Cap, rotor and coil
Vacuum leaks
Fuel pressure
Timing
Check the codes if it has any

And if none of that gets me anywhere I'll go to Pull-A-Part and grab as many TBI components as I can. The IAC, O2, TPS, MAP, etc. and start replacing them one at a time.

Am I forgetting anything? Or just maybe, am I lucky enough that this sounds familiar to someone who's dealt with this problem before?

Most of my experience with TBI involves removing it for a carb, but hopefully we're not at that stage yet. (And no Jamie "put a Ford engine in it" is not the solution I'm looking for...)

Thanks!

 

Check for vac leaks first.Pull a few plugs and see how they look(electrode wear wise)They will probably look crappy from the lousey runnig If you dont find any obvious issues there...Unplug the IAC and see if the thing idles.( If it straightens out, iac is pulling open to much) If that doesnt help...Check fuel pressure ( I doubt its fuel pressure it seems to run fine off idle ) Read any codes before you start unplugging things. Otherwise you may end up chaseing your tail.
As for the converter shuddering...This may be the cause of your woes. It may be locking up prematurely putting excessive load on the engine (Like not disengageing the clutch on a stick car when you come to a stop) There is a TCC solinoid on the side of the trans...This could be the issue or the converter may be failing. If so...Its time to go through the whole trans and get a new converter. It could also be a wire harness issue to the tcc solinoid as well. Just food for thought here: A missfire will cause the trans to drop in and out of OD causing a shudder soo. Drive it in drive not OD and see if the shudder continues... Theres ALOT more to add here but, I am certain many more will chime in with a plethora of info regarding the issues...Good luck!!!

PS: I love those suburbans...They are the BOMB!!! I want a 4X4 though...

I allmost forgot!!! Check the battery cables and any ancillary grounds you find. Low voltage will cause those tbi systems to run like poo poo...

 

Wow!! Look at that body!! It's a big one, but it's beautiful!!!

 

Thanks!

One more important symptom I forgot to mention - it's pinging under light throttle uphill, that's why I thought I should check the fuel pressure. Of course vacuum and timing would do that too...

As for the trans, I'm going to get the engine straight first, but it happens both in D and OD and I can make it stop with a light application of brake or throttle, so I feel pretty confident it's converter shudder.

 

Pull it out, and do the LS swap....Did I say that......OMG...what's happening to me???

 

Sometimes the EGR valve will stick open and cause a vac leak at idle and then make alot of pinging on acceleration.

 

I've a LOT of experience with these transmissions over the last 10 years or so since I've used them in several work vans(Astro/Safari).. and also my sbc Blazer. They have TONS of inherent flaws.. some of which have slowly been worked out in later gen's(4L60E on up). The good thing is that many of those same factory and aftermarket improvements can be used on older models since most are backwards compatible.

Based on that.. I really think Mavman nailed it in some of the above. I have a pretty good idea why the shudder is there and most are pretty easy fix's in the scheme of things which only involves digging into the TCC apply valve(accessed external of the pump housing).. and/or dropping the valvebody to apply them.

I'll try to keep it short(tough for me to do sometimes).. but I had an Astrovan about 7 years ago that actually started to stop and go into reverse as I was moving forward at slower speeds after 1st gear takeoff. Usually a pretty bad sign to say the least and I expected not to make it home from my work in Madison. But I let it cool down at a truck stop so the oil viscosity would increase somewhat and limped my way home with it since it seemed less problematic once cruising in OD on the highway. Got there.. pulled the pan and expected to find burnt clutch material and it wasn't bad at all considering the severity of the issue earlier.

So, I started digging deeper into possible causes and man was I shocked with all the potential valve/bore issues causing leaks and/or low pressure issues on the various circuits of this particular transmission. But after throwing every possible fix and update(including shift kit and billet servo's) at the transmisson which neared $600 bucks?(just for the parts alone).. it actually scratched 2nd gear and drove better than it ever had when it was brand spanking new! So, I did the exact same updates to the next 2 vans I bought as well.

I didn't buy everything from here.. http://www.transmissioncenter.net/performance_automotive.htm#Parts.. but it helped pinpoint some main issues that may be happening with my vans 4L60E and helped me to know what the hell I was even talking about when I picked the local transmission guys brain about the issues I was seeing and confirm where I should be spending my time and money. Then I went to my local transmission parts store to gather it all up. Transtar Industries.

I would start off with part #20T(in the above link) which doesn't require removing the valvebody.

Then from there it gets more difficult and I would use sonnax part # 77964-08k(they are also available individually as well for the 3-4 relay/shift valves but I can't locate them in my transtar catalog right now) to avoid the very common end plug leaks. Here's the Sonnax link. http://www.sonnax.com/system/announcement/77964-08K.pdf

And possibly more expensive part #'s 18D & 18E(also located in the first link) if the valve bore seems worn upon cleaning and inspection.

Depending on the mileage you may also want to consider a new seperator plate(check balls wear the holes out) and torlon check balls(or reuse the old steel ones on the new plate if they are still full round).

I can help a bit further if needed.. but am tight on time tonight and can't think back about all the details on such short notice. IMHO, the converter apply valves teflon seal and the o-ringed end plugs.. along with a good cleaning of the disassembled valvebody(not as bad as you think with a schematic and patience to set aside all parts in order).. should be enough to stop the shudder. But just in case.. you may want to get a premium rubber pan gasket in preparation/expectation of dropping the pan a few times to sneak up on the harder and more expensive fixes as you go from easiest/cheapest to harder/more expensive along the way.

PS.. I would NOT want to drive that truck for very long with a converter or clutch apply issue as it will cause you far more headeaches than tuneups and troubleshooting a miss.

Hope that helps.

 

egr valve sticking

 

I've had a lot of good suggestions here. Groberts I thank you especially for your insight on the transmission... Tomorrow I'll get into it, start with making the engine run right and go from there. I want to be sure what I think is TCC shudder isn't really just lugging an engine that runs rough under load at low RPM.

 

if it's the transmission, hope this takes care of it...

 

no problem.. I've been there too bud. Only started to work and rebuild these things later on in my life as I though it would just just spread my talents too thing to try and be proficient at too many things all at once. Wish I had started earlier since they can be much eaiser than the motors I do for mine and others. Hindsight, right? lol

As for the lugging possibility?.. that's sometimes the result of the TCC apply coming in to early which was touched on in earlier posts by myself(though I didn't go into detail there.. for once).. and Mavman. This can be caused by the cross leaks and improper stroking action(sticky valves) of the TCC apply valve.

I will warn you though that they can be PITA's to get out due to needing a long reach snap ring removal tool. I even had to custom make longer tips for mine just to make it a bit easier on my sanity after doing the first few.

Another method is to mod the line rise to be a bit more aggressive as that overrides some of the cross leaks and low pressure on the various circuits involved here. In my short experience so far and from talking to many pro builders.. with stock setups it's almost ALWAYS a cumulative loss and the sum of all issues is what causes them to act up intermittently and in various ways depending on driving style and temps.

 

Well I worked on the truck all weekend and into last night, and I have information...

First, in case you ever need to know, I found out after unsuccessfully plundering three different junkyards for a steering column, that a GM full size car (Caprice, LeSabre, Parisienne, etc.) has a steering column that's 99% identical. I wish I'd figured that out earlier in the game, as I didn't get to mess with the engine until late Sunday. I had to make a few changes but it worked very well.

Regarding the transmission and the shuddering... After unplugging the wiring for the converter lockup and going for a drive, I determined that the bucking I felt while the converter was locked wasn't caused by, but rather was amplified by the converter being locked up. The engine still ran rough at light throttle cruising in 3rd and 4th gear, I just didn't feel it as much without the lockup. So, that's good. The trans is probably ok.

And the engine. I still don't know what the problem is. But I do know it's not the EGR solenoid or valve, the IAC, the MAP sensor or the TPS. After replacing the EGR stuff it definitely got a little better, but I wouldn't say it's cured. Still thinking about it...

 

Pretty common and is exactly what Mavman already mentioned about just amplifying the miss at low speeds under premature lockup. The teflon sealed TCC apply valve I linked earlier should fix you right up.

 

I'm not sure there's actually anything to fix on the transmission at this point. Lockup seems to be happening at the right time, it's just making this apparent low-RPM miss more noticeable.

Maybe I ought to be focusing on the ignition system. I've yet to check the distributor cap, coil, wires...

 

...Well it ain't the plug wires. I checked the cap and rotor too. They didn't look new, but I'd hardly say they looked bad either. I looked at one plug, but maybe one of the others are ugly. I guess the coil is next.

I hate it when I'm at the "throw new parts at it until it works" phase, and it always seems to happen with EFI. This is exactly what I was trying to avoid.